Strategy for ecological corridor conservation and restoration in ...

Purpose,contextandbasics

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Strategy for ecological corridorconservation and restoration inthe Danube catchment

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Main authors (in alphabetic order)

GertrudHaidvogl – IHG/BOKU – AustriaCristinaMunteanu – WWF-Romania – RomaniaRalf Reinartz – IHG/BOKU & Büro für Fischereifragen und Gewässerökologie –Germany

With contributions of (in alphabetic order of countries)BorislavaMargaritova, Maria Kachamakova, Phillip Penchev – WWF Bulgaria – BulgariaZrinkaMesić – Karlovac University of Applied Sciences, Department of Hunting and NatureConservation – CroatiaLászló Berzi-Nagy, AttilaMozsár – Research Institute for Fisheries and Aquaculture – HungaryGheorghe Constantin, AndreeaHârceag, Mihail Costache, Doina Cioacă, Simona Pătruț –Ministry of Environment, Waters and Forests – RomaniaAndreeaDanciu – WWF-Romania – RomaniaGorčin Cvĳanović, Mirjana Lenhardt, Marĳa Smederevac-Lalić – University of Belgrade, Insti-tute of Multidisciplinary Research – SerbiaLadislav Pekarik – Trnava University, Faculty of Education – SlovakiaEva Horvat, Polona Pengal – Institute for Ichthyological and Ecological Research – Slovenia

Reviews and contributionsPeter Gammeltoft, Thomas Hein, Edith Hödl, Petra Repnik, Stefan Schmutz, Karl Schwaiger,Beate Striebel, Franz Wagner

Proofreading Michael Stachowitsch Layout Astrid Schmidt-Kloiber

Edited by University of Natural Resources and Life Sciences Vienna – BOKU

Copyright cover picture VERBUND 2020

This document was developed during the MEASURES project, co-funded by European Union(ERDF, IPA), Interreg – Danube Transnational Programme

Vienna, November 2021

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Authors and contributions

MEASURES contributed to securing andrestoring the Danube, its tributaries and rel-evant areas of the Danube Delta and theBlack Sea as functioning ecological corridorfor migratory fish. The project has docu-mented that numerous of these fish popula-tions are under pressure and have becomeextremely fragile due to fragmentation anddegradation of their migration corridorsand their habitats in the Danube River andits tributaries. Certain populations, includ-ing most native Danube sturgeon species,are on the verge of collapse as evidenced bythe assessments of Danube sturgeon popu-lations by the IUCN.

The decline of the once numerous migrat-ory fish populations in the Danube Basin isthe result of the cumulative impact of mul-tiple pressures: interruptions of river con-tinuity and changes in river hydrology andmorphology cutting off migration routes,degrading essential habitats and their ac-

cess routes, pollution and last, but not least,overfishing and poaching.

The project has identified a series of meas-ures (see below) to restore and protect eco-logical corridors for migratory species, re-build populations and reduce the risk oftheir collapse.

Certain pressures on populations (that arenot directly linked to the degradation ofhabitats and migration corridors) were notconsidered in MEASURES. They will needto be managed through measures other thanthose identified in this project to achieve thedesired target. They include pressure fromfishing, including illegal, unreported andunregulated (IUU) fishing, invasive alienspecies, pollution, climate change and oth-ers. Also, for diadromous species, habitatsand migration routes in the Black Sea werenot considered.

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Executive summary andpolicy outlook

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Implementation of ecological corridors with aprotected network of critical habitats to ensureself-sustaining populations of migratory fishthroughout the Danube Basin

Governance arrangements

Governance arrangements play a major rolein the degradation and rehabilitation ofconditions for migratory fish populations.The Danube migratory fish populations aresubject to the requirement of good ecolo-gical status of the EU’s Water FrameworkDirective. Migration corridors and the stateof habitats are therefore part of river basinmanagement responsibilities of the compet-ent national authorities. However, import-ant responsibilities with respect to migrat-ory fish species conservation may also liewith other authorities and it is therefore im-portant to clarify the distribution of re-sponsibilities:

● Ecological corridors for migratory fishare by their very nature alsotransboundary and cannot be managedby national measures alone. Thecompetent authority for transboundarywater management in the Danube Basinis the ICPDR. It has the powersnecessary to mandateDanube States totake measures to establish suchcorridors, including both continuitymeasures and habitat measures.

● Conservation of migratory fish is at thecrossroads between water managementand management of nature andbiodiversity. So far, the competentauthorities for the latter have playedlittle role in efforts to restore andconserve migratory fish species in theDanube Basin even though thecompetent authorities for nature andbiodiversity of all countries in theDanube Basin have adopted a Europeanwide Action Plan for sturgeon(PANEUAP) committing them toimplementing conservation actions.There is a need forDanube Basin States

to clarify the respective roles andresponsibilities of national nature andwater management.

● There are currently no legal obligationsto sustain fish populations by means ofconservation hatcheries and no clearlydefined responsible authorities. Giventheir nature and purpose, it is proposedthat nature protection authorities in theEU andDanube States concernedshould take responsibility for suchactivities, if appropriate together withfishery authorities.

● There are sectors outside river basinmanagement exerting a significant roleon the state of migratory fish species inthe Danube. There is a need to ensurethat policies and their implementationeffectively support the recovery andconservation of migratory fish species.The EU, the ICPDR and the EU-SDR(PA 06) should take the lead indeveloping this support (in particularfor sectors with transboundaryconsequences such as energy, climateand inland waterway transport) with aview to implementation by the relevantcompetent national authorities.

● Pressure from fishing in inland watershas an important impact on somepopulations, in particular sturgeons. Inspite of bans on sturgeon fisheries,poaching remains a problem.Enforcement of fishing bans thereforeneeds to be effective. This is a task forthe national authorities responsible forfisheries in inland waters.

● Risk levels for diadromous species in theDanube Basin are also influenced bymanagement of migration routes andhabitats in the sea. Very little is

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currently known about these routes andhabitats. The EU, competent nationalauthorities for marine fisheries, theBlack Sea Commission and the FAO-GFCMwill need to develop this issuewith a view to contributing to restoringand conserving sturgeon populations.

Priority measures

The project documents the key technicalmeasures needed to address bottlenecks forthe restoration of the ecological corridorswhich includes in particular

● re-establishing continuity of migrationcorridors where they have beeninterrupted, either by removal ofbarriers or establishment of appropriateconditions or facilities for fish passage

● restoration and maintenance ofdegraded essential habitats (spawning/juvenile/feeding etc.)

● operation of conservation hatcheries(“ex-situ facilities”) for native fishspecies and conservation stocking tostimulate the rebuilding of populationsand help prevent their collapse.

Chapter 5 of this document also identifies aseries of supportive measures for the imple-mentation of ecological corridors includingpopulation monitoring, legally binding na-tional river basin management and conser-vation plans, public participation, and in-creased use of green infrastructure.

The highest and most urgent priority meas-ures needed to establish ecological corridorsare:

1 – River continuity

● The Danube River currently has twomajor continuity blockages at the IronGate cutting off the Middle and UpperDanube from the Lower Danube and atGabčikovo cutting off the UpperDanube from the Middle Danube. Re-establishing fish passage at these twopoints is of basin-wide interest and willensure that fish can again migrate all theway from the Black Sea to the UpperDanube.

● The ICPDR and the Danube States areplanning to remove a considerablenumber of obstacles to river continuityin the wider Danube Basin in the2021-2027 period, based on identifiedpriorities for fish migration. This planshould be implemented, and rivercontinuity maintained as a priority.

2 – Conservation hatcheries (“ex-situ facil-ities”)

Conservation hatcheries are essential to pro-tect populations of critically endangeredsturgeon species against collapse. There isno need for hatcheries in all States althoughmultiple hatcheries will be needed to ensurethat failures due to exogenous factors donot result in collapse of populations. Put-ting in place financial support for conserva-tion both for their establishment and fortheir operation for an extended (multi-decadal) period will be essential due to thetime needed for the recovery of sturgeonpopulations.

Where there is a need to do so conservationhatcheries should be implemented for otherspecies, subject to assessments of the stateof populations.

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3 – Habitats and corridors

Known previous and current sturgeon hab-itats have been mapped for the Danubesturgeon species. At the level of the DanubeBasin habitat restoration is currently not thesubject of specific plans. The ICPDR andDanube States will need to continue theidentification of critical habitats, to developcriteria to set priorities for restoration, en-hance protection and maintenance of stur-geon and other migratory fish habitats aswell as the connecting corridors.

4 – Policy coordination

Enhance cooperation with policies in otherareas or sectors to ensure on national andon a basin-wide basis that past and futureefforts for protecting ecological corridorsare not undermined as a result of policy ini-tiatives in other areas (e.g. hydropower de-velopment, inland navigation or flood riskmanagement).

Furthermore, cooperation with relevantcompetent authorities of Black Sea Coun-tries and the Black Sea Commission has tobe enhanced to integrate the marine stagesof endangered and vulnerable diadromousspecies in protection efforts and manage-ment plans.

Supportive activities

● Establish basin-wide coordinatedpopulation monitoring (for diadromousspecies including monitoring in theBlack Sea) for endangered andvulnerable fish species (EU, ICPDR,Danube Basin States, Black Sea States,FAO-GFCM) as part of fish monitoringunder the Water Framework Directive;include future results in ICPDR TNMNYearbook, including results from regularand even continuous (automatic)registration of migratory fish at fishmigration facilities in Iron Gate,Gabčikovo and other well-chosenstrategic bottle necks and results fromDanube Delta.

● Public participation: information to anddialogue with the public concerned

● National Activity Plans to be integratedinto National River Basin ManagementPlans and other relevant managementplans should be developed with thecooperation of national natureprotection authorities. These Plans aswell as the proposed Local FishMigration Networks initiated to targetspecific local and regional aspects willbe strengthened by the enhancedcooperation with other sectorsinfluencing the conditions for migratoryfish. For sturgeon species, the PanEuropean Action Plan for sturgeonprovides a template applicable fornational activity plans.

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Tableofcontent

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Technical abstract ..........................................................................................9

01 Purpose, context and basics of this Strategy ........................................131.1 European water management and biodiversity legislation and guidelines.141.2 Linkage with relevant projects and initiatives ..........................................161.3 Actors and stakeholders involved in the development of this strategy .....171.4 Important topics not covered in detail by this Strategy .............................171.5 The ecological corridor for fish ................................................................181.6 The MEASURES project ............................................................................20

02 Overall goal and objectives ....................................................................21

03 Current status and impacts on the Danube ecological corridor formigratory fish ...............................................................................................233.1 The Danube River system .......................................................................233.2 River continuity and barriers ...................................................................253.3 Morphological status and habitat conditions ............................................253.4 Climate change and its effects on the Danube Ecological Corridor............273.5 Fish biodiversity ......................................................................................283.6 Examples for migratory fish species of the Danube ecological corridor.....29

04 Input for the Strategy – main results of MEASURES ..............................414.1 Mapping of potential habitats of selected migratory fish and habitat

verification ..............................................................................................414.2 Securing native stocks and further developing monitoring methods of

critically threatened Danube sturgeons ...................................................434.3 Stocking Sterlet and Russian Sturgeon in the middle and lower Danube ..434.4 Building ex-situ facilities .........................................................................444.5 Migratory fish in national and international strategic documents,

management and policy plans ................................................................454.6 Integration of and exchange with national stakeholders ...........................46

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4.7 Conclusions from the main results of MEASURES – what is needed toimprove the Danube ecological corridor and migratory fish ......................47

05 Types of Measures suggested for implementation.................................49ToM 1 – Mitigate or remediate the effects of migration barriers on the

ecological corridor ......................................................................57ToM 2 – Protect and restore habitats of migratory fish ............................61ToM 3 – Develop, promote and implement green infrastructure for flood

management and nature-based solutions for navigation ............64ToM 4 – Secure and support populations of sturgeon species and other

migratory fish by ex-situ measures.............................................67ToM 5 – Monitor connectivity, habitats and migratory fish populations ....71ToM 6 – Elaborate comprehensive National Activity Plans for Migratory

Fish Species ...............................................................................75ToM 7 – Strengthen “Local Migratory Fish Networks” ..............................78ToM 8 – Improve public participation and support for Local Migratory

Fish Networks.............................................................................81

06 Strategy implementation .......................................................................846.1 Indicators and monitoring of success.......................................................86

07 Challenges to take into consideration and risks of failure .....................88

08 Date of expiry and provision for an update ...........................................91

09 Annexes .................................................................................................929.1 Glossary .................................................................................................929.2 Abbreviations and acronyms ....................................................................969.3 MEASURES internal documents used ......................................................989.4 Literature and documents .......................................................................98

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The overall goal of this “Strategy for ecolo-gical corridor conservation and restorationin the Danube catchment” is to secure theDanube and its tributaries and relevantareas of the Danube Delta and Black Sea asan ecological corridor for migratory fishand to ensure conditions for stable or grow-ing populations. This means in particular toimprove ecological corridors with a net-work of critical habitats to ensure self-sus-taining populations of migratory fishthroughout the Danube Basin. The Strategyprovides the basis for defining the criteriafor the ecological corridor, identifying thiscorridor for the Danube and its tributaries,and developing measures and activities tosecure or, when necessary, restore the cor-ridor and its migratory fish populations.

Reaching the overall goal requires followingthree objectives, which also represent themain components of the ecological corridor

for migratory fish (physical connectivity;habitat availability, accessibility and con-tinuity; viable populations).

This Strategy offers a basin-wide frame-work and guidance for implementation,with an emphasis on national scales. Itrelates the concept of the ecological corridorto legal frameworks and EU targets as for-mulated especially in the Water FrameworkDirective, in the Biodiversity Directive, inthe Habitats Directive as well as in morespecific directives and strategies such as thePan-European Action Plan for Sturgeons, inthe EU-Strategy for the Danube Region, andin the transboundary agreements estab-lished by the International Commission forthe Protection of the Danube River (ICPDR;Chapter 2). River continuity interruptionsand habitat degradation due to human usesof the Danube River and subsequent tech-nical alterations of hydromorphological

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conditions have put severe pressures on mi-gratory fish. Sturgeon species are at thebrink of extinction, and many other migrat-ory fish are classified as threatened in atleast one of the countries contributing tothis strategy. In order to secure and restorethe Danube River as an ecological corridorfor migratory fish, the MEASURES projectaimed at filling major knowledge gaps onhabitats of migratory fish and on the con-servation of sturgeon species by means ofex-situ measures. Based on the findings,eight Types of Measures (ToM) were de-veloped to achieve improvement. TheseToMs form the core of the document(Chapter 5).

Three of the ToMs directly address the man-agement of the Danube River and its tribu-taries as an ecological corridor. ToM 1 callsfor assessing, mitigating or eliminating thenegative effects of migration barriers, ToM 2prompts for the protection and restorationof migratory fish habitats and ToM 3 forgreen infrastructure for flood managementand nature-based solutions for navigation.The latter topic was not dealt with explicitlyin MEASURES, but it targets important sec-tors (i.e. hydropower production, naviga-tion) that can potentially increase alreadyexisting pressures on the ecological cor-ridor. ToM 4 strives to secure and supportviable populations of migratory fish. Fi-nally, ToM 5 aims to improve and harmon-ise the monitoring of habitats and fish pop-ulations,

Further three of these ToMs are of organisa-tional and supportive nature: ToM 6 is ded-icated to developing, on country levels,comprehensive “National Activity Plans forMigratory Fish Species” going beyond themost urgent activities or the topics ad-dressed in MEASURES. ToM 7 proposes tocreate, establish and facilitate “Local Mi-gratory Fish Networks”. Such networksshould be composed of stakeholders from

different sectors to enable and ensure com-munication and their activities need to beembedded in established administrativeprocesses and structures. An importantbasis for these networks was set during theMEASURES project, and future activitiescan build on these. Finally, ToM 7 suggestsactivities to improve public participationand support for local migratory fish net-works.

The ToMs proposed in this Strategy are of ageneral nature. National and internationalpriorities are given, among them the highestpriorities have (1) re-establishing continuityeither by removal of barriers or by buildingappropriate facilities for fish passage, (2)protect or restore and maintain essentialhabitats (spawning/juvenile/feeding etc.)of migratory fish, (3) ensure the operation ofconservation hatcheries (“ex-situ facilities”)for native fish species and conservationstocking to stimulate the rebuilding of pop-ulations and help prevent their collapse.

The main addressees for implementation ofthis strategy are responsible authorities, inparticular water management and biod-iversity and nature protection authorities. Iffurther developed, Local Migratory FishNetworks can act as support and especiallyas an exchange platform for implementa-tion. In order to ensure transnational har-monisation of activities, these networksmust organise cooperation across theDanube basin well aligned with establishedmanagement procedures (e.g. WFD). Majorevents in the Danube basin, e.g. the AnnualFora of the EU-Strategy of the Danube Re-gion or the Danube Day, can be used forphysical meetings.

This Strategy proposes indicators to mon-itor its implementation and defines the ex-pected challenges. Among the most criticalpoints is the voluntary status of thisStrategy: making it a legally binding docu-

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ment on basin-wide and national levels wasneither a target of the MEASURES project,nor would the project duration of threeyears have offered sufficient time. Accord-ingly, the implementation of this Strategydepends largely on the cooperation andcommitment of the addressed stakeholders.In particular, the Associated Strategic Part-ners of the MEASURES project can play amajor role in this task.

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This basin-wide “Strategy for ecologicalcorridor conservation in the Danube catch-ment” (hereinafter referred to as “Strategy”)defines a framework to secure and restorethe Danube River and its tributaries as anecological corridor (eCOR). The focus is onecological connectivity, habitats of selectedmigratory fish and their populations. TheStrategy compiles existing and new know-ledge gained during the MEASURES projectand provides guidelines for the nationaland transnational management of key hab-itats of migratory fish to achieve an efficientconservation and re-establishment of ecolo-gical corridors. The Strategy brings atransnational additional value to theDanube Region because it addresses key ob-jectives and targets of several European dir-ectives and strategic documents (seeChapter 1.1).

The document addresses stakeholders con-cerned by and actively involved in the po-tential implementation of actions to secureand restore the Danube ecological corridorand migratory fish. This primarily includesvarious authorities, administrations and“practitioners” who are expected to planand implement measures to improve theecological corridor of the Danube and majortributaries for the benefit of the respectivemigratory fish.

The Strategy considers a timeframe of 7years, i.e. until 2027, following the revisioncycle of relevant management documents,in particular the Danube River Basin Man-agement Plan and national River BasinManagement Plans as major tools for imple-menting the WFD. It does, however, target along-term situation for migratory fish, espe-cially with regard to sturgeon species be-

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01 Purpose, context andbasics of this Strategy

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cause of their longevity, late maturation andthus decade-long population recovery.

Amain approach of this Strategy is todefine Types of Measures on a general leveland to provide more specific measures andactivities on national scales, which are partof the Annex to this Strategy. Establishing“Local Networks for Migratory Fish” anddeveloping “National Activity Plans for Mi-gratory Fish” are two Types of Measuresproposed, which are more of strategic andoverarching nature. They can be consideredas a means and prerequisite for successfulimplementation of the other Types of Meas-ures, defining at the same time tasks, cri-teria or tools for implementation. The im-plementation of measures should be en-sured by integrating them in existing man-agement and policy plans, strategic docu-ments and programmes, national legislationor any relevant public consultations (e.g.EIA, IAWB, EA, SEA procedures), e.g. dur-ing revisions or in future documents of thisnature.

This Strategy will be disseminated at thepolicy level in relevant countries and on atransnational level, aiming to raise govern-

mental and political support for embeddingecological corridors and key outputs of theMEASURES project into the future nationaland international legal and policy instru-ments (e.g. N2000 management plans, RB-MPs).

1.1 European water managementand biodiversity legislation andguidelines

The Strategy relates the concept of the eco-logical corridor to legal frameworks and EUtargets such as the EU-Strategy for Biod-iversity 2030, the Water Framework Direct-ive (WFD), the Flood Directive (FD), theHabitat Directive (HD), Marine StrategyFramework Directive (MSFD), the newEuropean Green Deal or more Danube spe-cific the European Strategy for the DanubeRegion.

For example, the new Biodiversity Strategyfor 2030 (BDS) calls in section ”Restoringfreshwater ecosystems” for greater efforts torestore freshwater ecosystems and the nat-ural functions of rivers in order to achievethe objectives of the Water Framework Dir-

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In a nutshell this Strategy● is a general framework that compiles the needs to conserve, strengthen andrestore the Danube ecological corridor for migratory fish and aligns it withthe existing legal framework

● makes the results of MEASURES applicable in practice● defines Types of Measures and activities● links aspects on basin and national levels● harmonises activities across countries● provides tools and guidance for the local networks for migratory fish, inwhich the major actors to implement the Strategy on national levels are en‐visaged to participate

● promotes the role of the ecological corridor and migratory fish

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ective. This can be done by removing barri-ers that prevent the passage of migratingfish or by making them passable, by im-proving the flow of water and sediments,and by restoring floodplains and wetlands.To help make this a reality, at least 25,000km of rivers will be restored into free-flowing rivers by 2030.

TheWater Framework Directive requiresestablishing River Basin Management Plans(RBMP). The RBMPs must describe the(ecological) status of water bodies, identifyexisting pressures and define measures howto achieve good ecological status or goodecological potential by 2027. In the case ofthe Danube, the International Commissionfor the Protection of the Danube River(ICPDR) is responsible to set up thetransnational Danube-RBMP (DRBMP).ICPDR works based on the Danube RiverProtection Convention (ICPDR 1994). Basedon a pressure analyses for the implementa-

tion of the WFD, it defined four SignificantWater Management Issues (SWMI): Organicand nutrient pollution, hazardous sub-stances pollution and hydromorphologicalalteration. According to the draft version ofthe DRBMP, Update 2021, to be publishedin December 2021, a fifth SWMI is envis-aged to be added, i.e. “Effects of climatechange”. The establishment of transnationalecological corridors and the reconnection offish habitats also constitute a major chal-lenge for improving environmental condi-tions in the DRB as outlined in the relevantplans of the ICPDR (DRBMP 2009, Update2015, ICPDR Ministerial Declaration 2016;DRBMP Update 2021, to be published inDecember 2021). Acknowledging the pre-carious status of sturgeons, ICPDR adoptedthe ICPDR Sturgeon Strategy in 2018(ICPDR 2018) with the goal of better under-standing and highlighting the challengesfaced by the Danube's sturgeon in order toadd to conservation efforts. It defines meas-


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Relevant targets of PA4 and PA6(EU-SDR Action Plan ((SWD(2020) 59) for conserving and restoring the eco‐logical corridor for migratory fish

PA4 - Action 5 Migratory Fish “Promote measures to enable fish migrationin the Danube River basin”● Raise broad public awareness and political commitment for the Danubesturgeons as flagship species for the Danube River basin and for the eco‐systems and biodiversity of the Danube River basin as a whole.

● Foster sturgeon conservation activities including protection of habitats, res‐toration of fish migration routes and ex-situ conservation measures

● Close knowledge gaps concerning monitoring of pressures and planning ofmeasures for fish migration in coordination with PA 6 (Action 3).

PA 6 - Action 3: „Develop and/or implement conservation action plansand/or management plans for endangered umbrella species of the DanubeRegion”:● Implementation of the Danube-related measures from the Pan-EuropeanAction Plan for sturgeon conservation will contribute to their protection andprotection of other freshwater species and their habitats.

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ures and activities that will support achiev-ing good ecological status or good ecolo-gical potential. The scope involves provid-ing an overview of actions and measuresconsidered necessary by sturgeon special-ists, in particular from the Danube SturgeonTask Force working towards securing thesurvival of sturgeons within the frameworkof “water competences” of the ICPDR. Thisinvolves fostering synergies and coopera-tion with all national and internationalplayers dedicated to sturgeon conservationactivities.

The Habitat Directive requires habitats des-ignation and management in accordancewith the ecological needs of the Annex IIspecies (Alosa spp., Acipenser sturio relevantfor this Strategy) and maintaining the fa-vourable conservation status of Annex Vspecies (Huso huso, Acipenser gueldenstaedtii,A. stellatus and A. ruthenus relevant for thisStrategy). Moreover, efforts are made at aninternational level to include additional leg-ally binding targets in the future EU NatureRestoration Law for the sturgeon speciescurrently covered by Annex V. The Strategydeveloped during the MEASURES projectprovides measures and activities contribut-ing to the adequate management and res-toration of Annex II species habitats, tostrengthen sturgeon populations, and anti-cipates conservation and restoration of stur-geon habitats from EU nature restorationlaw.

The topic of sturgeon and migratory fishconservation is a very important objectiveof the EU Strategy for the Danube Region(EU-SDR), for both Priority Areas (PA) 4(Water Quality) and PA 6 (Biodiversity andLandscapes, Quality of Air and Soils; see In-fobox).

While the above-mentioned strategies andstrategic documents clearly highlight theneed for the restoration of river continuity

and its importance for species conservation,the implementation process still needs aharmonised approach at the basin-widelevel and commitment on national as wellas on transnational levels.

This Strategy is further in line with thePAN-European Sturgeon Action Plan con-tributing to

● Objective 2 – Population structure isactively supported to reverse the decline

● Objective 3 – Sturgeon habitats areprotected and restored in key rivers

● Objective 4 – Sturgeon migration (up-and downstream) is secured orfacilitated

● Objective 5 – Timely and continuousdetection of population sizes andchanges in remaining wild stocks.

● Objective 8 – Sturgeons serve as flagshipspecies for healthy river ecosystems.Support from public, political actors,authorities and relevant stakeholders forconservation measures has increased.

1.2 Linkage with relevant projectsand initiatives

MEASURES and this Strategy build on theoutcomes of STURGENE (DSTF 2016), espe-cially on the extension/adoption of theroadmap and on linking ex-situ facilities.Another major basis development by theDanube Sturgeon Task Force, as an initiat-ive adopted by the EU-SDR Priority Area 6,is the Sturgeon 2020 programme – a pro-gramme for the protection and rehabilita-tion of Danube sturgeons formulated by theDanube Sturgeon Task Force (DSTF). Itserves as an important strategic instrumentof MEASURES and this Strategy, defining a

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comprehensive programme for Danubesturgeon protection.

A crucial aspect for the implementation ofan ecological corridor along the DR is alsothe close linkage to the network of protec-ted areas DANUBEPARKS and the projectDANUBEPARKSconnected. The provisionof important data from monitoring net-works by the ICPDR, Joint Danube Surveysand important links to the existing Danubedatabase provided strategic assistance. In-put is also expected from a planned feasibil-ity study for restoring fish migration at theIron Gate Dams I and II (WePass – openinglongitudinal connectivity at the Iron Gates).

Steps in counteracting sturgeon poachingand developing socio-economic measuresfor fishing communities have been made intwo LIFE projects coordinated by WWFATand covering 4 countries: Serbia, Bulgaria,Romania and Ukraine. The projects closedlegal gaps (i.e. no border controls of wildlifetrade in Ukraine), improved fishing regula-tions in Bulgaria and Ukraine, and intro-duced in January 2019 a new fishing ban forSterlet in Serbia. The engagement with andtraining for enforcement authorities resul-ted in increased control activities, mainly byvarious police departments, which are nowmotivated and equipped with the know-ledge needed to investigate illegal activities.Trust-building measures with 1000 fishers –the most affected target group of the fishingban – resulted in fishers sharing valuable in-formation about illegal activities in theircommunities. Also, business plans for al-ternative activities to fishing have been de-veloped in order to limit the poachingtemptation of sturgeon. Most importantly,the project provided evidence for ongoingillegal fishing and trade in all 4 countries, as30% of sturgeon products found on themarket were illegal and more than 200 casesof illegal fishing were compiled.

1.3 Actors and stakeholdersinvolved in the development of thisstrategy

The MEASURES project team, nationalworkshops, various actors and stakeholdergroups have been involved in developingthis Strategy. Basically, stakeholders con-cerned with the following topics have beenaddressed: nature protection, biodiversity,river management, flood protection, fishery,transport/navigation, hydropower as wellas researchers from fish and river ecology.The types of stakeholder groups and theirthematic scope differed in the workshopsorganised in the MEASURES partner coun-tries (Scherhaufer & Haidvogl 2021). Bey-ond this, an even wider group of actors andstakeholders shall be concerned with imple-menting this Strategy.

In national stakeholder workshops organ-ised during the MEASURES project, an im-portant foundation was set to ensure inputfrom and exchange between stakeholders aswell as a joint development of future meas-ures and activities (see details in Chapter 5).

1.4 Important topics not coveredin detail by this Strategy

The MEASURES project and this Strategydeal mainly with in-situ-, ex-situ-, manage-ment-related and policy topics. The follow-ing topics are closely connected with butnot specifically covered by this Strategy.They are, however, accounted for in closelylinked strategic documents and pro-grammes defining the rules and standardsin dealing with migratory fish, for exampleSturgeon 2020 or the Pan-European ActionPlan for Sturgeons under the Bern Conven-tion.


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● IUU Fishing (e.g. poaching, bycatch)and working towards a sturgeon catchmoratorium or a prolongation thereof(DSTF and WWF CEE activity)

● Acquiring political support for sturgeonconservation

● Capacity building and law enforcement:we will address capacity building forsome (creation of national networksduring the project) but not all potentialactivities; MEASURES will not intervenein improving or extending legaldocuments

● Socio-economic measures in support ofsturgeon conservation

Although the MEASURES Strategy does notcontain detailed measures and activities for

these topics, they are important elementsfor its success.

1.5 The ecological corridor forfish

The corridor as an ecological entity belongsto the category of habitat. Importantly, theconcept of a catchment or river basin as anecological corridor encompasses more thanthe physical waterbody as a migration routeor passageway for aquatic organisms. A cor-ridor also includes different categories ofhabitat, its inherent habitat use and hencealso “habitat-using”-fish populations, aswell as all processes and exchanges such asinformation (e.g. behavioural, genetic),turnovers (e.g. energy, biomass, bedload)necessary for the ecological functioning ofthe system to support viable populations of

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Figure 1: Components of the ecological corridor as perceived in this Strategy. The maincornerstones of this triangle also serve as levers for intervention to affect the status andfunctioning of the eCOR.

native fish and migratory species/ forms inparticular (Figure 1).

A viable ecological corridor includes thephysical connectivity within and betweenthe water bodies of the system, but also theecological “connectedness” of habitat, hab-itat use and populations. Thus, ecologicalconnectivity, apart from mere possibility ofbarriers, also comprises ecological function-ality as represented by natural or semi-nat-ural migratory fish habitats that are connec-ted and enable species-specific movementsto complete their life cycles as well as gene,energy and matter flow (e.g. DANUBE-PARKS 2019).

In this context, habitat is defined as both alocation and timing of habitat use, but alsoas a set of resources and conditions en-abling this use. Strategically, this promotes

the conservation and restoration of knownhabitat areas and seasons, as well as theprotection of certain conditions of potentialhabitats within the system.

Awell-functioning ecological corridor is anexcellent indicator for the ecological integ-rity and health of a catchment. It incorpor-ates not only river (and corridor) length, butalso other relevant basic and more complexfactors, conditions and gradients within thesystem. These include temperature, slope,dispersal patterns, impacts, pressures andbiodiversity.

In this document, the Danube River, its trib-utaries as well as the Black Sea form theecological corridor at the largest spatialscale. For the purpose of convenient plan-ning and implementation such as conduct-ing mitigation measures, ecological “sub-


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Figure 2: Tasks of MEASURES connected to the components of the ecological corridor. T1– T4: Workpackages of the MEASURES project. T1 addressed all three components of theecological corridor and provided overarching information.

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corridors” with regard to certain topics,areas, pressures and/ or species might bedefined and advanced.

1.6 The MEASURES project

The MEASURES project and the results ofits workpackages served as a basis for thisStrategy. This Strategy makes the findingsof the project “Managing and restoringaquatic EcologicAl corridors for migratoryfiSh species in the danUbe RivEr baSin”(MEASURES) applicable in practice bytransferring the results into measures andactivities. Key results such as a harmonisedmethodology for identifying key habitat(Workpackage T2) as well as conducting ex-situ measures to support endangered popu-lations and to conserve respective gene-pools by the release of juveniles from con-trolled propagation (Workpackage T3) wereconsidered in this document. A fully cus-tomised MEASURES Information Systemfacilitates access to targeted information forexperts, decision makers and the generalpublic (Workpackage T1). This InformationSystem also provides valuable informationfor implementing the Strategy. An analysisof selected management and policy plansunderlined the potential but also revealedgaps in existing policies on the national andtransnational level (Workpackage T4; Figure2). In spatial terms, the Danube River andall tributaries are addressed. Note, however,that only the middle and lower Danube and

selected sections of tributaries were subjectto detailed exemplary field investigationsduring the MEASURES project.

MEASURES took sturgeons (generaAcipenser and Huso), shad (Alosa spec.) andother migratory fish species such as Barbel(Barbus barbus), Vimba Bream (Vimba vimba)and Nase (Chondrostoma nasus) as flagshipspecies for all migrants of international rel-evance in the DRB. MEASURES thenworked on the options for establishingtransnational ecological corridors and sup-porting populations. This involved connect-ing (protected) habitats – encompassed bythe current network of protected areasalong the Danube River and major tributar-ies – with other critical hotspots for biod-iversity, and developing concerted meas-ures related to ex-situ conservation for en-dangered species.

Dealing with both in-situ- and ex-situ con-servation, the MEASURES project and thissubsequent Strategy are also strongly biod-iversity-related, as the ex-situ concept maybe defined as the “conservation of the compon-ents of biological diversity outside their naturalhabitats” and in-situ conservation as “conser-vation of ecosystems and natural habitats andthe maintenance and recovery of viable popula-tions of species in their natural surroundingsand, in the case of domesticates or cultivatedspecies, in the surroundings where they have de-veloped their distinctive properties” (Maxted2013).

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Purpose,context&

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The overall goal of this Strategy is to securethe Danube and its tributaries as an ecolo-gical corridor for migratory fish and to en-sure conditions for stable or growing pop-ulations. It lays the basis for defining thecriteria for the ecological corridor, identify-ing this corridor for the Danube and its trib-utaries, and developing measures and activ-ities to secure or when necessary restore thecorridor and its migratory fish populations.

Reaching the overall goal involves follow-ing three objectives, which also representthe main identified components of the eco-logical corridor for migratory fish.

● Physical connectivity

● Habitat availability, accessibility andcontinuity

● Viable populations

In order to achieve these objectives, thisStrategy describes Types of Measures,which evolved from the tasks and investiga-tions of the MEASURES project. In detail,the Types of Measures proposed below aimat (1) securing and restoring ecological cor-ridors (physical and ecological connectiv-ity), (2) identifying, securing, restoring andmanaging habitats of migratory fish and (3)identifying, securing, restoring and man-aging relevant target populations.

In order to ensure and promote the imple-mentation of the proposed Types of Meas-ures, groups of dedicated stakeholders mustbe formed on the national level. An import-ant basis for local stakeholder networks wasset in national workshops organised duringthe MEASURES project. Such local net-works should (further) develop the imple-mentation of the Types of Measures andactivities as defined in this Strategy and en-

Overallgoal&objectives

02 Overall goal and objectives

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Overallgoal&objectives

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Overallgoal&

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22

sure that topics not addressed here (seeChapter 1.4) are taken up. The local net-works should also raise public and politicalsupport. Furthermore, they are key forbasin-wide exchange and a harmonised im-plementation of measures and activities.

To support the implementation of theTypes of Measures described in Chapter 5

● Provides a guideline for Strategy useand implementation

● Prioritises measures and activities asspecified in an annex to this documenttime-wise, e.g. according to theirecological urgency, their complexity orwith respect to the working cycles ofmanagement and policy documents

● Defines measures and activities, whichcan be integrated in existing policy andmanagement plans at the local, nationaland basin-wide scale

● Provides guidance to competentauthorities and organisations forexisting policy on the national and basinlevel in order to achieve the goals ofrelevant European legislation

● Strives at harmonisation andstandardisation of measures andactivities on and between the local,national and basin-scale

● Accounts for avoiding and, if this is notpossible, mitigating adverse effects ofinfrastructure projects

● Provides a guideline for the evaluationof Strategy success

The followingmilestones for developing,implementing and evaluating/monitoringthe implementationwere identified accord-ing to their chronological sequence:

● Draft Strategy (completed duringMEASURES project)

● Stakeholder consultation and feedback(completed during MEASURES project)

● Final Strategy (completed duringMEASURES project)

● Incorporation into relevant legislative,policy and management plans(especially after MEASURES)

● Implementation of the Strategy’smeasures in practice (after MEASURES)

● Collection of feedback fromimplementation stakeholders (afterMEASURES, until 2027)

● Review of Strategy, new draft andStrategy 2.0 (after MEASURES, 2027)

A timely implementation of measures inthe Danube Basin will contribute signific-antly to meet the objectives of the EU Biod-iversity Strategy, of the EUWater Frame-work Directive and the EU Habitat Direct-ive.

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Overallgoal&

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3.1 The Danube River system

The Danube River is the second largest riverin Europe, with a drainage area of 805,000km2, a length of approximately 2,850 km,and an average discharge of 6,450 m3/s atits mouth. The whole catchment comprisesabout 10 % of continental Europe. TheDanube crosses or borders ten countries dir-ectly (Germany, Austria, Slovakia, Hungary,Croatia, Serbia, Bulgaria, Romania, Repub-lic of Moldova and Ukraine). The wholecatchment area touches the territories of 19different countries, 14 of which are repres-ented in the International Commission forthe Protection of the Danube River (ICPDR).A large diversity of landscapes and climatesare present within this area.

Geomorphological conditions define threedistinct river sections. The upper section(river km 2,850 – 1,790) ranges from Ger-

many to the border of Austria and Slovakiaand has an average slope of 40 cm/km,with a high bedload transport capacity. Be-fore regulation, the morphology of the riverin this section alternated between canyonswith narrow riparian zones (with the riverbreaking through massive layers of rock)and braided alluvial sections with manyside arms and backwaters in large flood-plains. This was especially true in Austria.The middle section (rkm 1,790 – 943) ischaracterised by a major reduction in slope(6 cm/km) and lower bedload transport ca-pacity. This section is separated from thelower section (river km 943 – 0) by a ca. 100-km-long cataract (the “Iron Gate”), wherethe river cuts through the CarpathianMountains. In the lower Danube River, theaverage slope is 3.9 cm/km and the depos-ition of suspended solids increases signific-antly (Keckeis & Schiemer 2002).

TheDanube:currentstatus

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03 Current status and impactson the Danube ecologicalcorridor for migratory fish

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The Danube River has 9 large tributaries,each with a catchment size above 20,000km2 and numerous smaller tributaries(Sommerwerk et al. 2009). A functioningconnection between the main river and thetributaries is as important as connectivitywithin the tributaries. These tributaries ex-hibit a wide range of ecological characterist-ics from small fast-flowing alpine headwa-ters up to large, low-gradient lowlandrivers. With respect to migratory fish, thefocus is mainly on the large and mid-sizedstreams.

Riverine ecosystems are the lifelines of theDanube River Basin (DRB). They are highlyvaluable in environmental terms (key ecolo-gical corridors). The mainstem Danube andits tributaries are key migration routes forsturgeons and other diadromous speciessuch as shads as well as potamodromous

fish, in particular cyprinids like Barbel andNase but also Sterlet (see below). These spe-cies are excellent bio-indicators for the eco-logical river quality due to their specificneeds and inherent habitat changes duringtheir long life-cycles. Especially the long-distance migrating sturgeons represent anatural heritage of the entire Danube Re-gion. Their dramatic decline in the last dec-ades has become an issue of basin-wide im-portance, documented by the Danube coun-tries and the European Commission.

Simultaneously, riverine ecosystems are life-lines in economic and social terms (e.g. nav-igation, hydropower, nuclear power plants,flood management, recreation, agriculture,fisheries), which causes increasing pressuresrelated to intense human uses (e.g. pollu-tion, hydromorphological alterations andfragmentation).

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Pressures of the DanubeEcological Corridor

Main pressures affecting fish biodiversity in the Danube River Basin cangenerally be grouped into the following major topics, according toSchiemer et al. (2003) and Kováč (2015):● Water quantity (e.g. water abstraction), quality and river engineering● River regulation and construction as well as operation of hydropowerdams

● Badly managed fisheries (esp. in the case of sturgeons) and a general lackof monitoring

● Invasive species

Main effects of these pressures are:● Extinction of species● High number of endangered species● Qualitative and quantitative decline of fisheries● Changes in fish composition, for example from habitat specialists (rheo‐philic and stagnophilic) to eurytopic forms

Most of these pressures are addressed on a basin-wide level becauseICPDR has identified Significant Water Management Issues (SWMIs) to ac‐count for major pressures in their DRBMPs.

Infobox

3.2 River continuity and barriers

One very important element of the ecolo-gical corridor is an unimpaired longitudinalconnectivity. Along the Danube and manytributaries, the implementation of river en-gineering projects and hydropower usehave interrupted river- and habitat continu-ity (see DRBMP, Update 2015; ICPDR 2015).This hinders aquatic organisms to access es-sential habitats such as spawning sites andfeeding grounds, disrupting their life-cyclesand threatening aquatic biodiversity.

Dams and hydropower plants in generalrepresent migration barriers and lead to thefragmentation of habitats for endangeredfish. Migratory fish species are particularlyaffected by this river fragmentation, beingunable to move up- and downstream or intotributaries between their required habitatsin different parts of the system. The ICPDRcounts 1030 continuity interruptions inDRBD rivers with catchment areas >4,000km2. More than half of these barriers arehydropower dams (614), whereas 284 stemfrom flood protection and navigation, and132 fulfil other purposes (e.g. water sup-ply). Together these barriers have a signific-ant and cumulative impact. About 7 % arelarge dams with water level differences ex-ceeding 15 m, 22 % result in water leveldifferences between 5 and 15 m, and almosthalf of them cause a water level differenceof less than 5 m (all data DRBMP, Update2015; ICPDR 2015). The latest values will bemade available with the DRBMP, Update2021 in December 2021.

Out of the total 771 water bodies in theDRBD, 317 are affected by barriers for fishmigration, of which 54 are passable for fish.258 water bodies in the DRBD are signific-antly altered by continuity interruptionsthat are un-passable for fish species. Thisrepresents 33 % of the total number ofDRBD water bodies.

Barriers put the function of the DanubeRiver Basin as an ecological corridor at riskby threatening the natural migration pat-terns of fish and by preventing access tospecies-specific habitat. According to theDRBMP Update 2015 (ICPDR 2015) only336 barriers were equipped with a func-tional fish pass, while at least 670 facilitiesclearly block fish migration.

This highlights a clear need to foster theconnectivity of habitats and promote the es-tablishment of ecological corridors to im-prove migratory paths of endangered fishspecies in the DRB. This calls for nationalactions as well as concerted, transnationalcooperation to prevent extirpations andmassive biodiversity loss and is thus a ma-jor topic of this Strategy.

Pressure mitigation and management ofbiodiversity requires an efficient monitoringof habitats (including fish migration facilit-ies) and populations because fish are thesingle most important bioindicator groupfor assessing the status of ecological integ-rity.

3.3 Morphological status andhabitat conditions

With the implementation of the EuropeanWater Framework Directive, the ecologicalstatus of surface waters and hence also thestatus and availability of habitat became animportant and mandatory environmentaltarget. This was also because, despite signi-ficant improvements in water quality, thetrend of declining freshwater biodiversitycould not be reversed (FAO 2019).

According to the Fish Migration Founda-tion, habitat degradation and habitat lossmake up over 45 % globally and about 60 %of the overall threat scenario for freshwatermigratory fishes in Europe (besides exploit-


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ation, invasive species & disease, pollutionand climate change) (Deinet et al. 2020).

Based on transnational surveys of theDanube it can be concluded that, in 2015,only 74 out of 771 water bodies were nearnatural or only slightly altered. A large pro-portion of the river is moderately (113 waterbodies) or extensively to severely (199 waterbodies) altered due to various river engin-

eering constructions (DRBMP, ICPDR 2015).No details on the morphological status wereavailable for the remaining water bodies.For the tributaries, case studies and surveysof the morphological conditions are avail-able, but not in the form of a comprehensiveoverview.

Habitats can be affected by a multitude ofimpacts such as dams (apart from being mi-

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Table 1: Four drivers of habitat change and their effects on sturgeon ecology (fromFriedrich et al. 2019; Zeiringer et al. 2018).

Driver Impact Effect

Dams

Migration barriersUpstream migration barrier for spawning migrationDownstream migration barrier for spent adultsDownstream migration barrier for juveniles

Change of downstreamhabitat Loss of spawning grounds in vicinity of dam

Change of habitat up‐stream‐impoundment

Interruption of upstream migration of spawning adults

Delay of downstream migration of juveniles & increasedrisk of predationLoss of spawning & nursing habitatReduced productivity

Water abstractionWater flow modification (e.g. reduction of flow velocity)Habitat degradation (e.g. change of substrate patterns,silting of interstitial, reduced water depth and width)

Hydropoweroperation

Migration barriers &change of habitat See "Dams"

Sediment flushingLoss of spawning & nursing habitatIncreased mortality of juvenilesReduced productivity

HydropeakingLoss of nursing habitatIncreased mortality of juvenilesReduced productivity

Turbine passage Increased mortality of adults and juveniles migrating down‐stream

Changes inHydromorpho-logy/River en-gineering

Straightening of river, lossof sidearms & backwaters

Habitat loss

Reduced productivityDeepening of river bed Habitat lossDredging Habitat destruction

Water carriageNavigation Vessel strikesDeepening of river bed See "Changes in hydromorphology"Migration barriers See "Dams"

gration barriers), infrastructure develop-ment, wetland drainage, floodplain discon-nection, abstraction of water or sand min-ing/ gravel extraction. Table 1 lists four ex-emplary drivers for habitat change andtheir effects on sturgeon ecology.

Recent studies show that restoration pro-jects aiming at creating static habitat fea-tures and characteristics have only limitedto no positive effects on aquatic biod-iversity. Positive effects may deteriorateeven further with time if the dynamic hy-dromorphological processes creating andrenewing habitat structures are not also ad-dressed by restoration measures (FAO2019).

3.4 Climate change and its effectson the Danube Ecological Corridor

For the Danube River catchment, climatechange scenario projections delivered ro-bust trends for the future hydrological run-off regime for the next 30 years. The sea-sonal stream-flow regime of the Danubeand its tributaries is predicted to changeconsiderably, particularly in the tributariesof the middle and lower Danube basin.There is a general trend towards a decreasein summer runoff for the whole Danubebasin and for autumn runoff for the middleand lower Danube basin, intensifying thealready existing low flow periods. Forwinter and early spring seasons, an increasein river runoff is projected, while some un-certainties for winter runoff in the DinaricAlps and the lower Danube basin still exist.

Large changes in the flow regimes of themainstem river and its tributaries will alsoshift environmental niches for biota with


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Climate Change and fish communities(Daufresne & Boët 2007, Pletterbauer et al. 2014, Stagl & Hattermann 2016)

Effects● New ecological conditions to which native biota may be adapted poorly orwhich exceed the tolerances of the native species

● Increased pressure by invasive species

Resulting in● Abundance shifts in current fish communities● Replacement of species● Range shifts within the catchment● Extirpation of species from the system

Calling for● Population monitoring● Evaluation and adaptation of conservation and restoration measures

Infobox

possible adverse effects for the freshwaterecosystem of river and floodplain and onhabitat and populations. These will even ex-ceed the negative effects of anthropogenicinfluence in disturbed sites (Daufresne &Boët 2007; Pletterbauer et al. 2014; Stagl &Hattermann 2015, 2016).

3.5 Fish biodiversity

The Danube River basin hosts a large vari-ety of fluvial habitats encompassing a richbiodiversity with many unique and en-demic species. Fast-flowing mountainstreams, wide and slowly flowing lowlandrivers, large sand and gravel banks, and in-stream islands host over 100 fish species,many of them in critically endangeredstatus due to habitat- and thus also life-cycle fragmentation.

Freshwater fishes are one of the most im-portant animal groups with regard tozoogeography and aquatic biodiversity be-cause they are confined to drainage sys-tems, which have been described as “dend-ritic islands of water surrounded by land, whichis in turn bordered by a saltwater barrier”(Berra 2007).

The Danube basin is a hot spot of biod-iversity and has the highest fish biod-iversity in Europe (Jungwirth et al. 2014,Sommerwerk et al. 2009). About 20 % of allEuropean species (Kottelat & Freyhof 2007)occur in the Danube drainage as a whole.Importantly, high diversities can also be ob-served on a local scale due to distinct longit-udinal and lateral environmental gradients.

The number of fish species in the DanubeRiver generally increases with distancefrom its source. No definitive total numberof native freshwater species in the basincannot be provided due to dynamic devel-opments in biology as a science and espe-cially the disciplines of systematics and tax-onomy. Kottelat & Freyhof (2009) currentlyassume a total number of 115 naturally oc-curring species of freshwater fish for theDanube basin, also taking into account thespecies from lakes and tributaries, as well asspecies displaying some tolerance to low sa-linities from estuarine/ brackish areas ofthe Delta and the Black Sea. A high nativediversity is reported from the Hungariansection, with up to 55 species living in thetransition zone between foothills and low-lands. Downstream, the number of speciesdoes not change until the lower Danubeand the Delta, where fish biodiversityreaches another peak. Today, the impoun-ded sections such as upstream of the IronGate dams are dominated by only feweurytopic species (Sommerwerk et al. 2009).

Larger and mid-sized tributaries also showa high fish species diversity. For example,the Slovenian section of the Mura River iscurrently inhabited by 61 species (fish andlampreys), of which 51 are indigenous(Povž 2016). The Sava River is home to 74fish and lamprey species, among them 15considered as non-native (Simonović et al.2015).

Despite this rich fish biodiversity in theEuropean context, habitat change and de-gradation negatively affects fish communit-ies in the Danube River system as well. Al-

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Table 2: Ecological status classes for all JDS4 sampling sites (Bammer et al. 2021).

high good moderate poor badSampling data sets (n) 9 20 9 9

Relative proportion (%) 19.15 42.55 19.15 19.15

though not focussing primarily on migrat-ory species, their populations and forms,the Joint Danube Surveys serve as good in-dicators for this.

Assessments of fish assemblages along theDanube and in selected tributaries (e.g. Ipel,Drava, Iskar, Jantra) during the JointDanube Survey in 2019 (JDS4) showed thatonly 19.2 % (nine out of 47 datasets) de-livered a good (fish) ecological status as de-manded by the Water Framework Directive.For 42.6% of the sites (20 sampling sites),only a moderate status was documented.Poor or bad status defined 9 sampling siteseach (19.2%, Table 2).

Focussing exclusively on the mainstemDanube, the situation becomes even worse,with only 8.5% (4 sites) reaching goodstatus, 46.9% (15 sites) moderate, 21.9% (7sites) poor and 18.8% (6 sites) bad status.

Relevant with regard to MEASURES andthis Strategy are the migratory fish speciesof the Danube basin, its ecological corridorsand thus by logic also the Danube Delta andparts of the Black Sea. Definitions of theterm “migratory” for fishes vary. In thiscase, it includes anadromous and potamo-dromous species with mandatory migratorylife-cycles (e.g. sturgeons and shad), butalso species forming both stationary andmigratory populations (e.g. Vimba Bream),as well as populations known to regularlyinclude groups or large numbers of migrat-ing individuals (e.g. cyprinids such as Naseand Barbel).

Migratory freshwater fish (including thesturgeons) are disproportionally threatenedcompared to other groups of fish. Globally,this group has declined by an average of76%, almost 50% in the two temperate re-gions of Europe and North America, andmost pronounced in Europe with 93%(Deinet et al./World Fish Migration Found-ation 2020).

3.6 Examples for migratory fishspecies of the Danube ecologicalcorridor(list of species considered in theMEASURES project)

Sixteen species from four different familieswere considered relevant for the MEAS-URES project by the partners in the eightcountries represented in the project (Aus-tria, Bulgaria, Croatia, Hungary, Romania,Serbia, Slovakia, Slovenia). Note that thedescription of fish species, especially withrespect to their respective conservationstatus, is limited to these countries. Furtherareas within the basin – like the GermanDanube and the Ukrainian part of theDanube Delta – have not been consideredand should be integrated in future updates.

The list of fish species dealt with by theMEASURES project comprises members oftypical families of migratory fish in theDanube River system. They are exemplaryfor the whole fish community and the eco-logical corridor of the Black Sea, the


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Figure 3: Abbreviations and colour codeused for individual fish descriptions. Datafor classification compiled by MEASURESpartners. All fish images courtesy of theFreshwater and Marine Image Bank,https://digitalcollections.lib.washington.edu

BS Black Sea currently occurring

LD Lower Danube status unclear – extinct orfunctionally extinct

MD Middle Danube X functionally extinct

UD Upper Danube extirpated

no natural occurrence

Danube Delta, the mainstem large rivers ofthe Danube basin and also some higher or-der tributaries.

They can be differentiated into the two ma-jor groups: anadromous migrants utilisingmarine, estuarine and riverine habitat, andpotamodromous species and populationsthriving and moving within fresh- and to acertain extent brackish water.

The following figures and tables provide anoverview of the families and species, theircurrent distribution and main ecologicaltraits (according to Jungwirth et al. 2003and EFI+-Consortium 2008), their nationalconsideration for the project, IUCN and na-tional threatened status (Figure 3), and oc-currence and use in aquaculture and/ orconservation breeding (Table 3; for detailssee Apostolos et al. 2020).

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Anadromous species

Acipenseridae

Sturgeons are the most iconic migratory fish species in the Danube River system.Three out of four anadromous species still exist in relict populations and are con-sidered by the MEASURES project.

Significance for the ecological corridor: These anadromous species and populationsdepend on the physical connectivity and habitat continuity within and between theBlack Sea, the Danube Delta and the mainstem riverine system of the Danube andits larger tributaries for their spawning migrations. Within this physical corridor,the species need appropriate currents and hard-bottom substrates for spawningand early development. Adults, subadults and juveniles during migration and dis-persal need interconnected feeding and nursery areas with high abundances ofprey organisms (e.g. fish, molluscs, invertebrates) in the river, the delta and the sea.The sturgeons are important ecological connector species between the open watersof the Black Sea (Beluga Sturgeon), its shallow areas on the continental shelf, theestuarine areas of delta and river, and the mainstem river system including thelarge tributaries.

The Beluga or Great Sturgeon (Huso huso) is the only true predator among Ponto-Caspian sturgeons, feeding mainly on fish in both fresh- and saltwater. This speciesonce travelled as far as the upper Danube in Bavaria during spawning migration.This species also attains the greatest overall sizes within this family and these wa-ters. Individuals start feeding on fish fry already as juveniles. The status of theGreat Sturgeon population is critical, although some juvenile specimens have beencaught in recent years as documented by the Danube Delta Reserva Authority andDanube Delta National Institute (DSTF 2020). IUCN classification CR. Habitats Dir-ective Annex V. Bern Convention Annex II. Bonn Convention Annex II. CITES Ap-pendix II.

The Russian or Danube Sturgeon (Acipenser gueldenstaedtii) was once a veryabundant species with an upstream migration from the Black Sea regularly reach-ing spawning sites in Slovakia and Hungary. Today, this species is confined to theBlack Sea, the Danube Delta and the mainstem river up to the Iron Gate gorge. Inregular monitorings in Romania, no natural reproduction could be documented for10 years, so that this species is considered to be functionally extinct. IUCN classi-fication CR. Habitats Directive Annex V. Bonn Convention Annex II. CITES Ap-pendix II.

The Stellate or Starry Sturgeon (Acipenser stellatus) regularly migrated as far asHungary. Its populations have also suffered from overexploitation and loss of hab-itat. IUCN classification CR. Habitats Directive Annex V. Bern Convention AnnexII. Bonn Convention Annex II. CITES Appendix II.


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Beluga or Great Sturgeon – Huso huso

main streamtributaries

BS LD MD UD

anadromouseurythermalrheophilicpiscivorouslithophilicrheopar

Russian or Danube Sturgeon – Acipenser gueldenstaedtii

X X main streamX tributariesBS LD MD UD

anadromouseurythermalrheophilicbenthi-insectivorouslithopelagophilicrheopar

Stellate or Starry Sturgeon – Acipenser stellatus


BS LD MD UD

anadromouseurythermalrheophilicbenthi-insectivorouslithopelagophilicrheopar

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Clupeidae

The members of the herring family or river herrings inhabit both sides of the At-lantic in North America and Europe, around the Mediterranean Sea, as well as inthe Black Sea and Caspian Sea basins and the Balkans.

Significance for the ecological corridor: These anadromous species and populationsdepend on the physical connectivity and habitat continuity within and between theBlack Sea, the Danube Delta and the mainstem Danube for their spawning migra-tions. Within this physical corridor, the species need appropriate currents and sitesfor spawning and early development. Adults, subadults and juveniles during mi-gration and dispersal need interconnected feeding and nursery areas with highabundances of prey organisms (e.g. fish, molluscs, invertebrates) in the river, thedelta and the sea. The shad are important ecological connector species between theshallow, well-lit areas of the continental shelf, the estuarine areas of delta and riverand the mainstem river system.

In previous centuries, the Pontic Shad (Alosa immaculata) migrated from theBlack Sea up to 1,425 km in the Danube River for spawning (as far as Bezdan inSerbia), before the blocking of the main migration route at the Iron Gate gorge. Thisspecies and its life-cycle may be characterised as marine pelagic-neritic andanadromous. Migrations include the continental shelf of the Black Sea at depthsbetween 3 and 90 m, spawning in freshwater, and important feeding areas foradults in the sea and brackish areas in the delta estuary for juveniles. It feeds onsmall fishes and crustaceans. IUCN classification VU. Habitats Directive Annex IIand V. Bern Convention Annex III and Revised Annex I of Resolution 6 (1998).

The Black Sea Shad (Alosa tanaica) has a similar life-cycle, yet did not migrate asfar upstream as the Pontic Shad. IUCN classification LC. Habitats Directive AnnexII and V. Bern Convention Revised Annex I of Resolution 6 (1998).

There are recent indications that shad individuals might be distributed even fur-ther, as eDNA-sampling has documented Alosa sp. at rkm 954 and in the tributaryRussenski Lom in Ruse (Bulgaria). There are also new records of the Black Sea

Pontic Shad – Alosa immaculata


BS LD MD UD

anadromouseurythermalrheophilicinsectivorouspelagophilicrheopar


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Salmonidae

The Black Sea Salmon (Salmo labrax) forms anadromous as well as potamodrom-ous riverine and lacustrine populations throughout its range. Little is known aboutthe ecology of the anadromous form in the Black Sea-Danube River system.

Significance for the ecological corridor: The Black Sea Salmon is an important eco-logical connector species between the Black Sea, the delta and the freshwater riversystem as far up as to the rhithral stretches of streams in hills and mountains.IUCN classification LC.

Shad upstream of the Iron Gate dam at rkm 871 from 2016 and 2019, potentially in-dicating the passing of ship locks for this species (unpublished data Lenhardt;Cokan et al. 2021).

Black Sea Shad – Alosa tanaica


BS LD MD UD

anadromouseurythermalrheophilicinsectivorouspelagophilicrheopar

Black Sea Salmon – Salmo labrax

ecology of Danube anadromous ecotype largely unknown


BS LD MD UD

anadromousstenothermalrheophilicinsecti-piscivorouslithophilicrheopar

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Potamodromous species

Acipenseridae

There are also potamodromous members of the sturgeon family in the system. Sig-nificance for the ecological corridor: These species and populations depend on thephysical connectivity and habitat continuity within and between the different partsof the Danube River system up to the Barbel zone. Within this physical corridor,the species need appropriate currents and sites for spawning and early develop-ment. Adults, subadults and juveniles during migration and dispersal need inter-connected feeding and nursing areas with high abundances of prey organisms (e.g.fish, molluscs, invertebrates) in the river. These potamodromous sturgeons are im-portant ecological connector species between the different parts of the DanubeRiver system.

The Ship Sturgeon (Acipenser nudiventris) forms both anadromous and potamo-dromous populations throughout its range. For the Danube system populationonly a potamodromous life-cycle has been reported. This is the most elusive stur-geon species of the Danube River system. It is considered extinct and only few in-dividuals were reported in the past decades. Sightings were documented in themainstem Danube, but also upstream in larger tributaries as far as the Barbel zone.(Current) IUCN classification CR; however, according to the new IUCN classifica-tion by the Sturgeon Specialist Group this species has to be considered extinct inthe Danube River (pers. comm. Ludwig 2020; IUCN letter to EU Commissioner).Habitats Directive Annex V. Bonn Convention Annex II. CITES Appendix II.

The Sterlet (Acipenser ruthenus) was once the sturgeon species with the widest dis-tribution within the Danube River system, besides the anadromous Beluga. Today,its distribution has become patchy, especially in the upper and middle Danubebasins. Current IUCN classification VU; however, according to the newest IUCNclassification by the Sturgeon Specialist Group, this species has to be consideredendangered in the Danube River (IUCN letter to EU Commissioner). Annex V. BernConvention Annex III. Bonn Convention Annex II. CITES Appendix II.

Ship Sturgeon – Acipenser nudiventris


BS LD MD UD

potamodromouseurythermalrheophilicbenthi-insectivorouslithopelagophilicrheopar


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Salmonidae

The Danube Salmon (Hucho hucho) once possibly formed a meta-population inthe Danube River system, with individual populations or population segmentsutilising habitat in the Danube mainstem system and tributaries from the Barbel asfar up as the Grayling zone. IUCN classification EN. Habitats Directive Annex IIand V. Bern Convention Annex III and Revised Annex I of Resolution 6 (1998).

Significance for the ecological corridor: The Danube Salmon is an important ecolo-gical connector species within the Danube River system and its tributaries becauseit is known to thrive in deep stretches of larger rivers with fast currents and highabundances of fish as potential prey, but also needs access to spawning sites in theGrayling zone.

Sterlet – Acipenser ruthenus


BS LD MD UD

potamodromouseurythermalrheophilicbenthi-insectivorouslithophilicrheopar

Danube Salmon – Hucho hucho


BS LD MD UD

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Cyprinidae

The carp family or Cyprinidae comprises numerous species, ecological preferencesand life-cycle strategies in the Danube River system. Ecologically healthy stretchesof the Danube River system down to the Delta are characterised by a high varietyof cyprinid species at different life stages from various ecological and reproductiveguilds. These species utilise a wide variety of naturally occurring ecological situ-ations and may travel long distances between suitable habitat for spawning andfeeding in the main river, but also use various lateral ecological situations likedifferent order tributaries, furcations and sidearms, connected and disconnectedbackwaters, as well as other types of water bodies in the floodplain.

Significance for the ecological corridor: The cyprinids in their different life stagesare important indicator and connector species of and for the availability and ac-cessibility of a variety of natural riverine and estuarine habitat in the system.

The Ziege or Sabre Carp (Pelecus cultratus) is a species that requires lateral struc-tures such as backwaters and tributaries during its life-cycle. It inhabits large low-land rivers, impoundments and littoral lakes, where it is known to migrate longdistances for feeding. IUCN classification LC. Habitats Directive Annex II and V.Bern Convention Annex II and Revised Annex I of Resolution 6 (1998).

The Vimba Bream (Vimba vimba) is a potamodromous species, yet includes somesemi-anadromous populations that migrate upstream from brackish into freshwa-ter rivers for spawning. Nonetheless, rheophilic freshwater populations also existin the Danube. Similarly to Nase, they spawn in schools in fast-moving stretcheswith stony or gravelly substrate and little vegetation. IUCN classification LC. BernConvention Annex III.

Ziege or Sabre Carp – Pelecus cultratus


BS LD MD UD

potamodromouseurythermaleurytopicplanktivorouspelagophiliclimnopar

The Nase (Chondrostoma nasus) is a rheophilic species inhabiting the deeper wa-ter of the Barbel and Grayling zones of main rivers with swift currents, often ingroups in the backwaters of shore structures or in rocky outcrops. It dwells nearthe bottom, where it grazes on (diatom) algae, aquatic plants and invertebrates. Itspawns in fast-flowing stretches over gravelly or stony substrates, but may also mi-grate into smaller tributaries for reproduction. IUCN classification LC. Bern Con-vention Annex III.

The Barbel (Barbus barbus) is a rheophilic bottom dweller and lives in fast-flowingrivers with gravel or stone substrates, which it also uses for spawning. IUCN clas-sification LC. Habitats Directive Annex V.


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Vimba Bream – Vimba vimba


BS LD MD UD

potamodromouseurythermalrheophilicinsecti-omnivorouslithophilicrheopar

Nase – Chondrostoma nasus


BS LD MD UD

potamodromouseurythermalrheophilicdetriti-herbivorouslithophilicrheopar

Barbel – Barbus barbus


BS LD MD UD

potamodromouseurythermalrheophilicinsectivorouslithophilicrheopar

Little is known about the ecology of the Cactus Roach (Rutilus virgo), a rheophilicspecies inhabiting medium to large rivers near the bottom. IUCN classification LC.Habitats Directive Annex II (under the name R. pigus).

The Asp (Leuciscus aspius) inhabits lakes, larger rivers and especially the lowerreaches and estuaries. Adults dwell at the surface of fast-flowing stretches, wherethey prey on fish. As juveniles, this species needs connected backwaters to com-plete its life-cycle. IUCN classification LC. Habitats Directive Annex II and V. BernConvention Annex III.

The Danube Carp (Cyprinus carpio carpio) in the project context refers to the ori-ginal wild variety of this species present in the Danube River system, not the vari-ous domesticated strains. Its current status remains unclear. IUCN classificationDanube River subpopulation CR.

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Cactus Roach – Rutilus virgo


BS LD MD UD

potamodromouseurythermalrheophilicinsectivorousphytophilicrheopar

Asp – Leuciscus aspius


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Danube Carp – Cyprinus carpio carpio


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potamodromouseurythermaleurytopicomnivorousphytophiliclimnopar

Legend Table 3 (next page):grey cells: the species has not been worked on by partners from the respective countrygreen cells: (officially known) ex-situ initiatives/experience and/or release of specimens in the wild for population sup‐port of the respective speciesyellow cells: (officially known) captive broodstock of respective species used solely for commercial purposes oraquaculture

Conservation categories/status:EX – extinct; RE – regionally extinct; CR – critically endangered; EN – endangered; VU – vulnerable; LC – least concernSI: R – rare species/potentially endangered (ranljiva vrsta); E – endangered species/significantly endangered (ogroženavrsta oziroma prizadeta vrsta)HR: SP – strictly protected species; TBC – temporary ban on catch; МLC – minimal length for catchRS: SPWS – strictly protected in the wild; PWS – protected wild species; PBC – permanent ban on catch; TBC – tem‐porary ban on catch; МLC – minimal length for catch; DC - daily catchHU: HP – highly protected, P – protected; NC – not protected, yet not catchable; N – not protectedSK: RE – regionally extinct

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Country RO BG RS HR SI HU SK AT

Anadromous species

AcipenseridaeBeluga / Great Sturgeon(Huso huso) CR CR CR SPWS

PBCRESP

very rareP RE

Russian / DanubeSturgeon(Acipenser gueldenstaedtii)

CR CR CR SPWSPBC

RESP RE very rare

P CR

Stellate Sturgeon(A. stellatus) CR CR CR SPWS

PBCRESP

very rareP RE

ClupeidaePontic Shad(Alosa immaculata) VU VU CR SPWS

PBCDDSP P

Black Sea Shad(A. tanaica) LC DD SPWS

PBC SP

SalmonidaeBlack Sea Salmon(Salmo labrax) CR not

observednot

evaluated RE

Potamodromous species

AcipenseridaeShip Sturgeon(A. nudiventris) CR EX CR SPWS

PBCRESP

very rareP RE

Sterlet(A. ruthenus) VU EN VU PWS

PBCVU TBCMLC R stable

NC LC CR

CyprinidaeZiege, Sabre Carp(Pelecus cultratus) VU DD R NT

Vimba Bream(Vimba vimba) N/A LC PWS

TBC MLC VU E N NT VU

Nase(Chondrostoma nasus) N/A

LC PWSTBC MLC

DCLC E N NT NT

Barbel(Barbus barbus) LC VU

LC PWSTBC MLC

DCLCMLC E N LC NT

Cactus Roach(Rutilus virgo)

LC PWSTBC MLC

DC

NT(as

R. pigus)E rare

P VU EN

Asp(Leuciscus aspius) LC VU

LC PWSTBC MLC

DCVU TBCMLC E N LC EN

Danube Carp(Cyprinus carpio carpio) CR

LC PWSTBC MLC

DCEN TBCMLC E N CR EN

Salmonidae

Danube salmon(Hucho hucho) EN

EN PWSTBC MLC

DCENTBC E very rare

HP VU EN

Table 3: Overview of migratory fish species considered by partners in the MEASURES project and theirnational conservation status al. 2018).

During the MEASURES project, valuablebasic information about the Danube systemas an ecological corridor was created. Somekey results are briefly described below. Fur-ther details can be found in the deliverablesand outputs for the specific workpackagesas noted in the respective sections.

4.1 Mapping of potential habitatsof selected migratory fish andhabitat verification

During MEASURES, potential and actualspawning, nursery, feeding, wintering andresting habitats of selected migratory spe-cies were identified. For potential habitatidentification, various sources such as re-ports, field protocols or museum specimenswere used. Furthermore, maps, aerial andsatellite images, bathymetry maps and fieldmeasurements were analysed based on eco-

logical traits of species. The actual use ofpotential habitats was verified by analysingthe results of (previous) field surveys andusing different types of sampling gear aswell as tagging. The task considered the fishspecies mentioned in Chapter 3 but the fo-cus was on sturgeon habitats (Figure 4). Forall fish species, about 2,200 locations in theDanube and selected tributaries were iden-tified as potential habitat, of which roughly50 % could be confirmed as actual habitatduring MEASURES field work and previ-ous surveys.

Despite the huge joint effort enabled in theMEASURES project, knowledge gaps interms of migratory fish habitats still exist.For example, a compilation of existingknowledge about habitat conditions on na-tional scales is missing and is an importantsubject of future work.

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Some further information is available inChapter 3.3 and in Cokan et al. (2021).

The MEASURES project accomplished pilotactions following a harmonised methodo-logy. Accordingly, neither the list of poten-tial habitats nor that of actually used habit-ats is complete. With respect to obtaining anoverview on the status or distribution of therespective species on the scale of theDanube region, one can conclude that:

● During MEASURES, selected sections ofthe Danube and tributaries wereinvestigated. Thus, knowledge gapsremain in terms of potential and actuallyused habitats and habitat types forsturgeon and shad species in theDanube River and in investigatedtributary sections. These gaps are evenlarger for the potamodromous species.

● Only a small proportion of potentialhabitats were sampled during theMEASURES pilot actions in the field.Thus, the presence of the targetedmigratory fish species could bedocumented for only a fraction of thesehabitats. The reasons for this includesampling techniques and timing or toosmall fish populations.

● More information and knowledge onhabitat, especially for thepotamodromous species, mightpotentially be retrieved by examiningfurther documents not readily availablethrough ordinary sources, e.g. in greyliterature.

● The results, in combination with theanalysis of Management and PolicyPlans, strategic documents and

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Figure 4: Confirmed Sturgeon Habitats in the Danube River Basin before and after theConstruction of the Iron Gate dams.

infrastructure projects, lead to theconclusion that many actual andpotential habitat sites lack sufficientprotection.

● Finally, migration barriers must be madepassable in order to secure a functionalecological corridor and to ensure thecompletion of the life-cycle of migratoryfish and a sufficient exchange within thegene pool.

4.2 Securing native stocks andfurther developing monitoringmethods of critically threatenedDanube sturgeons

Securing native populations of Danubesturgeon is a pressing task because thenumber of individuals for most species isvery low and the ship sturgeon is probablyextinct in the Danube catchment. The in-formation on Russian sturgeons gatheredover the last decade shows that this speciesis functionally extinct in the Danube Basinand the neighbouring Black Sea.

Thus, collecting and keeping of broodstockand its genetic analysis are a major pre-requisite for re-establishing and supportingsturgeon populations. Ex-situ gene stockskeep viable sturgeon populations undersafe and controlled conditions over longerperiods. These captive populations harbourbroodfish, which are frequently propagatedfor continuous releases of genetically suit-able juveniles that are fit for survival in thewild to strengthen the remaining wild stur-geon populations or for reintroduction intoformerly inhabited parts of the system.

The state of the art and knowledge wascompiled in a “genetic manual”, whichprovides among others a protocol forbroodstock management and breeding(Reinartz 2021).

eDNA-markers for monitoring purposeswere identified for Sterlet (Acipenserruthenus) and Ship Sturgeon (A. nudiventris)and tested at selected Danube sites. Noproof of A. nudiventris was possible, but thepresence of Stellate sturgeon, for which aneDNAmarker was already available, andSterlet could be documented based oneDNA sampling.

4.3 Stocking Sterlet and RussianSturgeon in the middle and lowerDanube

The highly endangered status of sturgeonspecies in the Danube calls for both long-term and short-term actions. The stockingof wild populations with additional indi-viduals serves as a short-term supportingeffort for the sturgeon species. In this con-text, the ex-situ gene stocks referred toabove are a backbone of the revitalisationmeasures, but to ensure an ideal geneticbackground, broodfish collection and sub-sequent genetic analyses are necessary aswell.

In the MEASURES project, two sturgeonspecies were selected for these activitiesbased on their relatively well accessiblepopulations. Sterlet broodstock was collec-ted in Hungary (10 specimens) in 2020 andtransported to NAIK-HAKI, which main-tains a Sterlet gene stock in Hungary. AsRussian Sturgeon broodstock was not avail-able in Hungary, 3,000 fertilised eggs werepurchased in Romania in 2020 and trans-ported to BOKU for further rearing. Surviv-ing fry were split between BOKU andNAIK-HAKI to share the responsibility andinfrastructural demand of rearing them tolarger sizes.

During stocking events, artificially rearedindividuals are released back into their nat-ural habitat. In Hungary, Sterlet juveniles

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were released in 2019 (5,000 specimens) andin 2020 (1,500 specimens). Furthermore,24,000 Sterlet fry were released into the trib-utaries of Danube in 2020. Russian Stur-geons were available in Romania in ad-equate numbers. DDNI purchased 1-yearold juveniles each year from 2019 to 2020for Russian Sturgeon stocking events. Therelease of Russian Sturgeon juveniles tookplace in Romania in 2019 (1,500 individu-als), spring 2020 (300 individuals), and inautumn 2020 (700 individuals). All releasedfish of both species (except the fry due totheir small size) were tagged with internaltags or external anchor tags. This methodenables tracking released individuals overlonger periods. For tagging, Floy external T-bar anchor Tags (Sterlet) as well as CodedWire Tags, PIT tags or Floy external T-baranchor Tags (Russian Sturgeon) were used.These tags include ID numbers to identifythe released fish if caught at another loca-tion in the future.

So far, individuals from both species wererecaptured and reported. The experimentalSterlet restocking proved to be successful:17 tagged Sterlet specimens released in Bajaand Ercsi in April 2019 were caught in Ser-bia a few weeks after release. Furthermore,nine specimens released in Baja in May 2020were caught in Serbia in July 2020. This sug-gests the rapid spread of the restocked fish.On one hand, this decreases their chance tobe preyed, on the other hand it makes theirrecapture challenging. Therefore, the citizenrecapture data play a crucial role in evaluat-ing the success of restocking. During the re-capture survey in Hungary, some Sterletspecimens were caught but none of themwere tagged. Russian Sturgeon were repor-ted in the Chilia branch (near Vilkovo) inOctober 2020.

4.4 Building ex-situ facilities

In order to create adequate and specialisedex-situ facilities to rear Danube sturgeonspecies for conservation and restocking, ascouting mission was conducted in 2019 byBOKU and NAIK-HAKI. Existing sturgeonex-situ gene stocks and their diverse infra-structural environments were visited in Italy(“Pisano Dossi” fishfarm, “Storioni Ticino”fishfarm, “Naviglio” fishfarm) and Germany(“Landesforschungsanstalt für Land-wirtschaft und Fischerei” in Born/ Mecklen-burg-Vorpommern, “Leibniz-Institute forGewasserökologie und Binnenfischerei” inBerlin). The discussions focused on thetypes of water supply (semi-flow-through orRAS systems), filtering and cleaning, feed-ing and lighting conditions as well as onbiological characteristics related to the sizeof a well-functioning ex-situ system. Theadvantages and disadvantages of the sys-tems were analysed. The conclusion wasthat different sturgeon species require vari-ous environmental settings – there is nogeneral “sturgeon” setting.

With respect to ex-situ activities and (re-)stocking, one can summarise that conserva-tion restocking has to integrate genetic per-spectives. This is because the genetic integ-rity of recipient native populations is a key-stone factor for long-term, sustainable con-servation. The genetic survey of the sterletgene bank in NAIK HAKI consisted of wildcaught specimens and revealed similaritybetween the gene bank-originated sterletsand wild caught (from different locationsand rivers) specimens in terms of popula-tion genetics. The conclusion is that there isdominance of heterozygotes in the studiedpopulations, including the sterlet brood-stock in the gene bank of HAKI. The min-imal broodstock size and the mating designare crucial in ex-situ conservation, and bothmust be based on the genetic traits. Thismakes a genetic manual, which provides a

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guide for the genotype-based ex-situ con-servation. very important for ex-situ conser-vation. The broodstock holding and prepar-ation of specimens for propagation are alsocrucial steps of ex-situ conservation.

4.5 Migratory fish in national andinternational strategic documents,management and policy plans

During the MEASURES project (WP T4), na-tional, regional and international manage-ment and policy plans as well as strategydocuments from the policy sectors "conser-vation", "sustainable development", "fisher-ies", "river basin management", "flood riskmanagement" along with "transport" and"hydropower" were analysed. For the pro-ject and the Strategy, it was of special in-terest whether these documents consideredrivers and especially the Danube River sys-tem as ecological corridors for migratoryfish. The analysis yielded the following in-sights:

● The situation differs significantlybetween the countries in the Danubebasin.

● The conservation of migratory fishspecies, the protection of their habitats,and rivers as ecological corridors arecovered in most of the countries in theirconservation policy, biodiversity targetsor river management, particularly withregard to the implementation of WFDrequirements.

● Plans on the national or regional leveloften do not explicitly target theecological corridor and migratory fishspecies. This reflects the often generalnature of national conservation andbiodiversity policy plans rather than adisregard towards migratory fish andthe ecological corridor.

● The most important kind of plans in thedifferent countries for migratory fishand the ecological corridor were theofficial River Basin Management Plans.Such Plans integrated these twoecological aspects in assessments andsubsequently encompassed them inhabitat protection or mitigation andrestoration measures.

● Management and policy plans are amajor tool to balance the (oftenconflicting) interests of different riveruses and respective stakeholders.

Apart from documenting the acknowledge-ment of the ecological corridor and its pop-ulations of migratory fish in official docu-ments, however, the analysis also revealed anumber of deficits that remain to be dealtwith.

● In general, major deficits in themanagement and policy plans withregard to the ecological corridor andmigratory fish relate to theirimplementation. This is a commonsituation for conservation andrestoration targets. Weaknesses in theimplementation of a plan can refer toincomplete implementation in practice,failure to update plans according tochanged policies and laws, as well asmissing legal approval.

● Several strategies or plans need a moreexplicit integration of habitat and fishprotection or restoration measures. Thetargets of different types of legal,strategic and management documentsare conflicting and must be betterharmonised.

● Often, weaknesses or deficits stem fromaccompanying “soft” measures. Theseinclude financing and training thenecessary personnel, missing funding

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possibilities (esp. for measures todirectly protect fish and habitats orrestore them) or insufficient integrationof concerned stakeholders.

● Data related to migratory fish fromvarious types of monitoring toadequately assess the current ecologicalconditions are lacking in practice. This isthe case even if such assessments arerequired by e.g. nature and biodiversityprotection plans or river basinmanagement.

● In some cases, baseline data areavailable, but subsequent effects ofprotection and restoration measures orinfrastructure constructions are notmonitored and documented.

● Progress in implementing protectionand restoration measures is often notappropriate to reach the ecologicaltargets given in specific documents.

● In some countries, migratory fish are notconsidered in the ecological statusassessment according to the WFD.

● Current water-engineering measurespose an ongoing threat to the ecologicalcorridor and migratory fish in allcountries.

● Some ongoing infrastructure projects(navigation, hydropower) should be(re-)evaluated and their negative effectson the ecological corridor should beestimated.

● Future river-engineering projects fornavigation and hydropower production,currently being implemented orplanned, will further negatively impactthe ecological corridor and migratoryfish populations in many countries (seeabove, subchapter on pressures).

● Additional threats outside thegeographical and thematic scope of theMEASURES project affect migratory fishpopulations and/or the ecologicalcorridor. In the lower Danube, forexample, IUU fishery poses a seriousthreat and increases the extinction risk,especially for sturgeons.

● These deficits call for a structuredresponse in theory and practice. Thisincludes amending the respectiveofficial documents and strategies, aswell as implementing the proposedmeasures of the Strategy. Within itsframework, this will have to include thedevelopment of specific regional,national and international Action Plansfor the Danube ecological corridor andmigratory fish species. Similarapproaches and efforts for e.g. sturgeonspecies (Acipenseridae) or the DanubeSalmon/Huchen (Hucho hucho) canserve as best practice examples. Finally,it is an indispensable for future policyand management to respect minimumecological requirements as well as toidentify and promote compromisesolutions.

4.6 Integration of and exchangewith national stakeholders

Integrating stakeholders was a core interestof the MEASURES project. The aim was toachieve a shared understanding of the pro-ject results and implementation at the na-tional and basin level, as well as to improvethe implementation process, feedback anddata collection. The framework of stake-holder integration was defined in a “stake-holder strategy”. This was agreed amongMEASURES partners at the beginning ofthe project and a list of important stake-holder organisations was compiled. Thestakeholder groups considered were related

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to nature protection/conservation/restora-tion, river management/flood protection,fishery, hydropower, navigation and agri-culture/forestry.

People from national and regional authorit-ies and administrations, private and publicenterprises, as well as NGOs, associationsand researchers were invited to participatein three workshops which were organisedduring MEASURES in each partner country.Stakeholders were thus able to follow theprogress of the project, to interact and dis-cuss results, and in particular to contributeto the development of a harmonisedStrategy and its implementation. Compar-ing the results of the national workshops inthe eight MEASURES partner countries re-veals substantial differences in terms of co-operation between stakeholders from differ-ent thematic areas as well as institutionallevels.

In each country, the respective local stake-holder group forms a pool of potentialmembers for the Local Migratory Fish Net-works, which shall play a key role in the im-plementation of this Strategy.

4.7 Conclusions from the mainresults of MEASURES – what isneeded to improve the Danubeecological corridor and migratoryfish

The Types of Measures proposed in thisStrategy focus on the above-described res-ults of the MEASURES project and in partic-ular on the identified gaps. Based on these,eight Types of Measures were defined. Theyare described in the following chapter on ageneral level, and national and transna-tional priorities are highlighted. More de-tails for the specific activities can be foundin the annex.

In order to integrate those threats for theecological corridor and migratory fish spe-cies that were not taken into account inMEASURES (e.g. fisheries), we propose asan overarching and first type of measure todevelop “National Activity Plans for Mi-gratory Fish Species”. The stakeholderworkshops organised during MEASUREScan be taken as a basis for developing suchNational Activity Plans.

Table 4 depicts how the conclusions, i.e. theidentified gaps and necessities as identifiedby MEASURES, translate into implement-able measures and activities of the Strategy.

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Table 4: How identified gaps and necessities translate into Types of Measures.

Gaps and necessities identified Type of Measure

● In most countries, no consistent and stableorganisational structures to protect and restore theecological corridor and migratory fish exist

● Creating, establishing and facilitating “LocalMigratory Fish Networks”

● Overarching strategy for the ecological corridor andmigratory fish missing in most countries

● Developing and implementing comprehensiveNational Activity Plans for Migratory Fish Species

● Gaps in monitoring of actual/potential habitats;mapping

● Monitoring of migratory fish species and theirhabitats

● Conservation of habitats often not secured by policyand management plans

● Habitats threatened by infrastructure projects● Verification if implementation of management andpolicy plans are effective often missing

● Protecting and restoring habitats of migratory fish

● Impacts and passability of individual migrationbarriers are only partly known, especially in theDanube tributaries

● Assessing and mitigating or eliminating effects ofmigration barriers on the ecological corridor

● Up to now, there are no state-of-the-art ex-situprogrammes and facilities functioning according tostandards agreed upon by the scientific community

● The population structure and natural reproduction ofendangered fish species needs to be supported byreleases of juveniles from controlled andconservation-oriented propagation

● Securing and supporting populations of sturgeonspecies and other migratory fish

● Establishment of local networks fails among othersdue to lack of funding, interest conflicts amongdifferent water use sectors but also publicperception

● Improving public participation and support for localmigratory fish networks

● Infrastructure built for flood protection, navigation orhydropower use is still often purely technical andcontinues to threaten the ecological corridor andmigratory fish

● Developing, promoting and implementing greeninfrastructure for flood management and nature-based solutions for navigation

The overall goal of this Strategy is to securethe Danube and its tributaries as an ecolo-gical corridor for migratory fish and to en-sure conditions for stable or growing fishpopulations. This Strategy lays the basis fordefining the criteria for the ecological cor-ridor, identifying this corridor for theDanube and its tributaries, and developingmeasures and activities to secure or whennecessary restore the corridor and its mi-gratory fish populations.

Reaching the overall goal involves pursuingthree objectives, which also represent themain identified components of the ecolo-gical corridor for migratory fish.

● Physical connectivity

● Habitat availability, accessibility andcontinuity

● Viable populations

MEASURES has documented that numer-ous Danube migratory fish populations areunder pressure and have become extremelyfragile due to fragmentation of their migra-tion corridors and their habitats. Certainpopulations, including most native Danubesturgeon species, are on the verge of col-lapse as evidenced by the IUCN assess-ments of Danube sturgeon populations.

The decline of the once numerous migrat-ory fish populations in the Danube Basin isthe result of the cumulative impact of mul-tiple pressures: interruptions of river con-tinuity and changes in river hydrology andmorphology that cut off migration routes,degrading essential habitats and their ac-cess routes, pollution and last, but not least,overfishing.

The MEASURES project has identified aseries of measures (see below) to restoreand protect ecological corridors for migrat-

TypesofM

easures

05 Types of Measuressuggested forimplementation

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ory species, rebuild populations and reducethe risk of their collapse. Certain pressureson populations (i.e. those not directly linkedto the degradation of habitats and migra-tion corridors) were not considered in theproject. They will need to be managedthrough measures other than those identi-fied here. They include pressure from fish-ing, including IUU fishing, invasive alienspecies and pollution. Moreover, fordiadromous species, habitats and migrationroutes in the Black Sea were not considered.

Governance arrangements play a major rolein the degradation of conditions for migrat-ory fish populations. The Danube ecologicalcorridor – integrating migratory fish popula-tions – is subject to the requirement of goodecological status of the EU’s Water Frame-work Directive. Migration corridors and thestate of habitats are therefore part of theriver basin management responsibilities ofthe competent national authorities. Import-antly, however, key responsibilities with re-spect to migratory fish species conservationlie with other authorities. This makes it ne-cessary to clarify the distribution of respons-ibilities (see Chapter 6). Concerned authorit-ies and institutions as main users of thisStrategy should link up with other sectors toalso tackle these topics. This would help toavoid any doubling of conservational effortand to take advantage of existing synergies.Enhanced cooperation with policies in otherareas or sectors ensures, on a basin-widebasis, that restored continuity and habitatsare maintained and that the many unde-graded corridors and habitats do not deteri-orate as a result of policy initiatives in othersectors (e.g. hydropower development, in-land navigation or flood risk management).Furthermore, cooperation with Black SeaCountries and the Black Sea Commissionmust be enhanced to develop the protectionof endangered and vulnerable diadromousspecies.

In order to transfer the results of MEAS-URES into practice, this Strategy providesguidance to competent authorities andstakeholders on the national level and basinlevel (for example to ICPDR) for existingpolicy. This pertains especially to consider-ing further river basin management plan-ning as well as nature or biodiversity pro-tection in order to achieve the objectives ofrelevant European legislation, as given ascontext in Chapter 1 of this document.

The Strategy documents the key technicalmeasures needed to address bottlenecks forthe restoration of the ecological corridors. Inparticular, this includes

● re-establishing continuity of migrationcorridors where they have beeninterrupted, either by removing barriersor establishing appropriate conditionsor facilities for fish passage

● restoration and maintenance ofdegraded essential habitats (spawning/juvenile/feeding etc.)

● operation of conservation hatcheries(“ex-situ facilities”) for native fishspecies and restocking to stimulate therebuilding of populations and helpprevent their collapse

In order to achieve these overarching tar-gets, eight Types of Measures (ToM) are de-scribed (Figure 5). Five of these ToMs relatedirectly to conservation and restoration ofthe three main pillars of the ecological cor-ridor:

● ToM 1 – Mitigate or remediate theecological impact of migration barriers(relates to pillar “connectivity” of theeCor)

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● ToM 2 – Protect and restore habitats ofmigratory fish (relates to pillar “habitat”of the eCor)

● ToM 3 – Implement green infrastructureand nature-based solutions (relates topillar “habitat” of the eCor)

● ToM 4 – Secure and support populationswith ex-situ measures (relates to pillar“populations” of the eCor)

● ToM 5 – Monitor connectivity, habitatsand populations (relates to all threepillars of the eCor)

Three further ToMs are of organisationalnature and support the implementation ofthe above-mentioned ToMs:

● ToM 6 – Develop comprehensiveNational Activity Plans for migratoryfish species

● ToM 7 – Establish or further developLocal Migratory Fish Networks

● ToM 8 – Improve public participationand support for Local Migratory FishNetworks

On the level of ToMs, all have high prioritybecause all three pillars of the ecologicalcorridor are severely negatively affected byhuman pressures. Importantly, only whenall three pillars are addressed equally canthe overall goal be achieved. Also, on theorganisational level, the three ToMs areequally important to support the successfulimplementation of the technical ToMs.

Table 5 presents an overview of the ToMs.The following subchapters define, for everyType of Measure, the targets, the rationalebased on the MEASURES project, as well asaddressees and transnational and nationalpriorities. The transnational and the na-tional levels are closely linked for ecological

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Figure 5: The eight Types of Measures proposed in this Strategy and their link to the threemain pillars of the ecological corridor.

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Table 5: Overview of the Types of Measures (ToM). The objectives refer (1) to the elementsof the ecological corridor (eCOR) addressed by a ToM; (2) the main outputs of theMEASURES project providing further details (these documents can be found at:http://www.interregdanube.eu/approved-projects/measures/outputs); (3) importanttransnational strategic documents.

Type of measure TargetRationale

–––––––––––––––––––––––––––––––––––––––Key actions

ToM 1. Mitigate or re‐mediate the effects ofmigration barriers onthe ecological corridor

Restore physical con‐tinuity and ensure fishpassage at barriers

Barriers obstruct the movement and migration ofpopulations and individuals.–––––––––––––––––––––––––––––––––––––––

Prevent new barriers, remove barriers, build fishpassages

ToM 2. Protect and re‐store habitats of mi‐gratory fish

Ensure habitat availabil‐ity, accessibility andecological continuity

Habitat protection and restoration is indispens‐able to improve the ecological corridor and en‐sure migratory fish conservation. As a prerequis‐ite, good monitoring programmes should be inplace.–––––––––––––––––––––––––––––––––––––––

Identify habitat, restore and/or protect

ToM 3. Develop, pro‐mote and implementgreen infrastructure forflood managementand nature-basedsolutions for navigation

Ensure the protectionand enhancement ofnature and natural pro‐cesses

Green infrastructure promotes methods to ensuree.g. flood management and navigation using in‐tegration of natural and nature-based methods.–––––––––––––––––––––––––––––––––––––––

Develop and implement green infrastructure solu‐tions

ToM 4. Secure andsupport populations ofsturgeon species andother migratory fish byex-situ measures

Save populations fromextinction

Endangered populations need protection in thewild, but sometimes also supportive ex-situmeasures for rebuilding population structure byreleasing genetically suitable individuals from con‐trolled propagation.–––––––––––––––––––––––––––––––––––––––

Develop and implement ex-situ programmes andfacilities

ToM 5. Monitor mi‐gratory fish popula‐tions and their habitats

Ensure knowledge-based management ofpopulations and habitat

Research and monitoring of populations andhabitat is the basic prerequisite for any kind ofpopulation and habitat management.–––––––––––––––––––––––––––––––––––––––

Develop and implement habitat and populationmonitoring

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Type ofmeasure

1.Objective (reference to ecologicalcorridor/eCOR)

2.MEASURES project results3. Strategic documents

Spatial scale –international, basin wide,national

ToM 1. 1. All three elements of the eCOR2. None3. EU-Biodiversity Strategy, Pan-EuropeanAction Plan for Sturgeons, EU-SDRAction Plan, DRBMP (ICPDR)

● Basin-wide● Pilot activities on regional andnational levels

ToM 2. 1. Habitat2. Habitat map, habitat manual3. Pan-European Action Plan forSturgeons, EU-SDR Action Plan,DRBMP (ICPDR)

● Sub-basin, if required by naturaldistribution or reintroduction

● Local

ToM 3. 1. All three elements of the eCOR2. None3. Pan-European Action Plan forSturgeons, EU-SDR Action Plan,DRBMP (ICPDR), Flood directive, WFD

● Sub-basin● Local

ToM 4. 1. Viable populations2. Ex-situ manual3. Pan-European Action Plan forSturgeons, EU-SDR Action Plan

● Basin-wide● Transnational because populationscross borders

● Sub-basin, if required by naturaldistribution or reintroduction

● Mirror- or twinning facilities indifferent parts of the basinpossible, if close coordination isensured

ToM 5. 1. Viable populations, habitat2. Habitat map, habitat manual3. Pan-European Action Plan forSturgeons, EU-SDR Action Plan,DRBMP (ICPDR), Habitats Directive(reporting)

● Basin-wide● Pilot activities on regional andnational levels

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Table 5: continued.

Type of measure TargetRationale

–––––––––––––––––––––––––––––––––––––––Key actions

ToM 6. Elaboratecomprehensive Na‐tional Activity Plans forMigratory Fish Species

Ensure applicability ofthe Strategy also on na‐tional level

National Activity Plans for Migratory Fish Species(NAP-MFS) ensure consistent targets, activitiesand implementation on the national scale. Theyallow accounting for local and regional specificsand for international and basin-wide targets andframework conditions.NAP-MFS should be built based on the MEAS‐URES Strategy. In MEASURES partner countries,local networks can initiate the NAP-MFS.–––––––––––––––––––––––––––––––––––––––

Develop NAP-MFS

ToM 7. Strengthen“Local Migratory FishNetworks”

Create structures of ex‐pertise and responsibil‐ity

Well-established Local Migratory Fish Networksensure the implementation of the NAP-MFS. Theycan act as exchange and cooperation platformson basin-wide or even European scale. They al‐low a timely reaction if framework conditionschange.–––––––––––––––––––––––––––––––––––––––

Establish LMFNs and a basin-wide overarchingstructure

ToM 8. Improve publicparticipation and sup‐port for Local Migrat‐ory Fish Networks

Ensure public, stake‐holder and political sup‐port

Public participation directly engages the public indecision-making and gives full consideration topublic input in making that decision. With in‐creasing complexity of subjects, such as eCorconservation and restoration, the variety of in‐terests emerging from different kinds of organisa‐tions increases.–––––––––––––––––––––––––––––––––––––––

Create public, stakeholder and political aware‐ness

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Type ofmeasure

1.Objective (reference to ecologicalcorridor/eCOR)

2.MEASURES project results3. Strategic documents

Spatial scale –international, basin wide,national

ToM 6. 1. All three elements of the eCOR2. Outputs on "Developing stakeholdercooperation" and "Lessons learnedfrom MEASURES”

3. Pan-European Action Plan forSturgeons, EU-SDR Action Plan

● National● Basin-wide harmonisation

ToM 7. 1. All three elements of the eCOR2. Outputs on "Developing stakeholdercooperation" and "Lessons learnedfrom MEASURES”


● National● Basin-wide harmonisation andexchange

ToM 8. 1. All three elements of the eCOR2. Stakeholder list, externalcommunication strategy


● Transnational● National

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as well as for management and organisa-tional reasons. For example, fish ecologicalrequirements with respect to migration donot follow national boundaries. Further-more, monitoring requires harmonisationand exchange on the basin level. To monitorsturgeon habitats, a joint methodology hasbeen identified and tested during theMEASURES project in selected sections ofthe Danube and certain tributaries. On thenational scales, adaptations might be neces-sary and monitoring must be implemented.For every ToM a more detailed description

is given along with a list of useful mile-stones to assess the implementation processand its progress. Finally, the connex isshown to the EU-SAP, the EU-SDR (PAs 4and 6) and the DRBMP as a major existingstrategic documents. An annex to this docu-ment provides specific examples for na-tional activities as identified during threerounds of national workshops in everyMEASURES partner country.

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Mitigate or remediate the effects of migration barriers onthe ecological corridorToM 1

Target • Restore physical continuity and ensure fish passage at barriers.

Rationale • Barriers obstruct the movement and migration of populations and in-dividuals. Although MEASURES did not investigate connectivity and migrationbarriers in detail, there is sufficient knowledge on the detrimental effect of suchobstacles on migratory fish. As “connectivity” is one of the three main pillars of anecological corridor (hereafter eCor), re-opening migration routes is an indispens-able component of eCor protection and restoration.

Principal addressees • Competent authorities and institutions involved in watermanagement on basin and national levels, especially authorities responsible for es-tablishing the River Basin Management Plans; hydropower companies.

National and international priorities

● Restore connectivity at the Iron Gates and Gabčikovo dams to re-establishmigration between the lower and middle and towards the upper Danube

● Restore connectivity at other obstacles blocking access to habitats alreadyidentified as critical by MEASURE

● Initiate pilot activities to remove barriers in tributaries

● Restore long cross-border stretches of physical and ecological continuity (seealso ToM 2)

● Monitor the functionality of existing fish passages, especially on the chain ofhydropower plants on the Sava River

● Implement multifunctional passage solutions (e.g. as passage and habitat)whenever possible

● Ensure migration in impounded sections

● Ensure nation-wide barrier identification and passability surveys to developbarrier catalogues, including identification of obsolete barriers to be removed

● In order to support the implementation of these priorities

● Allocate appropriate resources to ensure that ecological corridors in large riverswork well for upstream migration as well as for downstream migration, wherea number of open questions still require clarification

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● Allocate appropriate funds for the remediation of these obstacles to fishmigration

● Put in place appropriate administrative mechanisms (such as periodic reportingin Annual meetings of ICPDR on progress) to ensure no further delays inremediation

● Ensure information exchange, capacity building, harmonisation ofmethodologies, international/ transnational synchronisation and coordinationof activities

Description • Almost all fish species mi-grate on a regular basis, yet fish do notchoose to be migratory. That is a funda-mental and intrinsic trait of fishes on thespecies, population and individual levels.This is obvious for explicit migratory spe-cies such as sturgeons and shad, whose life-cycles extend over hundreds or even thou-sands of kilometres and varying ecosystemsin the sea, estuaries and rivers. Nonetheless,migration is also important on the level ofpopulations and even individuals of semi-and supposedly non-migratory species.

Migration barriers obstruct these move-ments and migrations of species, popula-tions and individuals. They prohibit thecompletion of the life-cycle for mandatoryreproductive migrants (e.g. sturgeons,shad), but also migrations by all species fore.g. dispersal, feeding, repopulation as wellas balancing biomass and genetic exchangebetween different parts of the system ingeneral. The dispersal aspect of ALL fishspecies is especially important becausesmall, isolated populations have a lower re-silience and therefore higher extinction risk.While migratory fish are generally goodswimmers, many of the “non-migratory”species have very limited swimming capab-ilities, but still depend on dispersal to main-tain genetic diversity and stable meta-popu-lations.

Any man-made structure (barriers, intakes,groins, dykes etc.) in the aquatic environ-

ment can potentially impact fish migration.Some examples for migration barriers arehydropower dams, perched culverts andpassages, emerged and submerged sills aswell as weirs and sedimentation zones withreduced oxygen contents or steep temperat-ure gradients on the longitudinal axis of theriver (PAN-EUAP, 2018). River embank-ments, flood protection dams, and the dis-connection of lateral sidearms and thefloodplain – in many cases interconnectedwith hydropower dams – also hamper mi-gration on a lateral axis.

In identifying barriers, this calls for consid-ering that these may often be physical suchas dams and weirs, but can also be biolo-gical/ecological, physical and chemical. Ex-amples include thermal barriers, waterlevel fluctuations, areas of unnaturally highpredation/mortality, and hostile conditionsfor rheophilic species in impoundments.

Several decades of establishing and monit-oring fish migration aids have yieldedguidelines for upstream migration solutionsthat can be used for many fish species (e.g.Schmutz & Mielach 2013). Each barrier,however, has to be assessed in terms of im-pacts, purpose and ecological settings todefine the optimal migration solution. Andknowledge is limited for some species. Es-pecially for sturgeons, no off-the-shelf spe-cifications or "one-size-fits-all" passing solu-tions are typically available. This mightalso apply for the Danube Salmon.

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This makes it mandatory to conduct at leasta basic feasibility study for each migrationbarrier. Such studies must describe and ana-lyse the current state and enable the devel-opment of a predictive balance of differentpassing solutions for the safe up- anddownstream passage of all aquatic speciesand life stages. This includes quantifyingimportant aspects of the targeted system fordecision-making.

Such aspects comprise individual and cu-mulative impacts of the barrier on generalecological parameters such as hydrologicaland temperature regime as well as sedimenttransport. This also calls for addressing spe-cific impacts on the presence of fish speciesand populations up- and downstream of thebarrier and on aquatic habitat and habitatuse, fish behaviour up- and downstream ofthe dam and main routes of approach. Thelocation of entrances and alternatives in thetechnical layout of passage ways must alsobe considered (e.g. by telemetry and/or hy-droacoustics). Additional mitigation meas-ures, such as habitat restoration in the vicin-ity of the obstacle or the construction of ad-ditional new habitat (e.g. artificial spawninggrounds) should also be included. Finally,additional impacts on the system like cli-mate change and future infrastructural de-velopment and use should be considered.The key for the function of any passingsolution is the amount of water and spacethat is made available (PAN-EUAP, 2018).Accordingly, options related to removing oradjusting barriers that prevent the passageof migrating fish and improving the flow ofwater and sediments must be assessed.

Milestones to assess ToM-implementation

1.1. Pre-feasibility studies for fish migrationare included in all future barrier construc-tion projects

1.2. The effect of physical and other barrierson the ecological corridor have been as-sessed

1.3. Prioritisation methods on the nationaland international scale are available toidentify the need for action as determinedby the natural distribution and movementsof the target species of endangered migrat-ory fish.

1.4. Options for barrier and dam removalhave been assessed as a first choice to re-es-tablish physical and ecological continuity

1.5. Passing solutions have been developedand implemented at barriers as a secondchoice, functioning at all times, for all spe-cies, sizes and developmental stages of thetarget species as well as functioning up- anddownstream.

1.6. A common database on barriers andtheir passing solutions has been created, im-plemented and is maintained with open ac-cess for all involved stakeholders

1.7. Methodologies for assessment, imple-mentation and function control of barrier/dam removal and establishing passing solu-tions have been standardised and harmon-ised.

1.8. Water abstraction and impoundmentpermits have been reviewed to implementthe ecological flow in order to achieve goodecological status or potential of all surfacewaters and good status of all groundwaterby 2027 at the latest, as required by the Wa-ter Framework Directive

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Figure 6: At the hydropower plant Ottensheim-Wilhering in Austria, the Austrian hydropower companyVERBUND built in recent years a more than 14-km-long bypass system with the support of a LIFE+ pro‐ject. The bypass system fulfils the requirements of fish migration and also serves as a habitat. Such solu‐tions are a first choice among migration facilities but they require sufficient place along a river section.When no place is available, e.g. in gorge sections, technical facilities might be an option (Photo: VER‐BUND 2020).

The Pan-European Action Plan for Sturgeons (PAN-EUAP) - Objective 4:Sturgeon migration (up-and downstream) is secured or facilitated.

EU-SDR-Action Plan – PA 4 – Water quality: Action 5: Migratory fish.

EU-SDR-Action Plan – PA 6 – Biodiversity and landscapes, quality of air andsoils: Action 3: Develop and/or implement conservation action plans and/ormanagement plans for endangered umbrella species of the Danube Region.

DRBMP-update 2021, Joint Program of Measures, Interruptions of River Con-tinuity

links to…

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Protect and restore habitats of migratory fishToM 2Target • Ensure habitat availability, accessibility and ecological continuity. Habitatconditions in the Danube ecological corridor ensure that all types of habitatsspawning, nursery, feeding, wintering, etc.) of migratory fish exist to a sufficientextent, i.e. they support viable populations. With respect to ToM 1, open migrationroutes must ensure accessibility to and between these habitats.

Rationale • Habitat restoration is indispensable to improve the ecological corridorand ensure migratory fish conservation. MEASURES has developed and tested ap-proaches to identify and verify different types of habitats for migratory fish. In thecountries represented in the project, a core set of potential and actual sturgeon hab-itats was recorded. These form the basis for habitat protection and restoration andhelp to guide the remediation of migration obstacles. Further efforts are considerednecessary to identify key habitats of migratory fish for protection and restorationefforts.

Principal addressees • Competent authorities, institutions, initiatives and net-works in water management, nature and biodiversity protection at international(e.g. European Commission, EU-SDR – PA 6, Berne Convention), basin-wide(ICPDR) and national levels;


● Protect sturgeon habitats already identified by MEASURE as critical with theset of legislation in place at the national as well at the international level (e.g.Nature 2000 areas/HD)

● Ensure habitat protection and when necessary restoration for key migratoryfish species such as Nase, Barbel and Danube Salmon, especially in Natura2000areas (e.g. Mura River)

● Fill knowledge gaps on habitats of all migratory fish (ToM 5) and protect thesehabitats, especially for threatened species

● In order to support the implementation of these priorities

● EU and EU-SDR are called upon to ensure protection of migratory fish againstpotential impacts of new policies and projects, and to strengthen cooperationacross different sectors (water, nature conservation, hydropower, navigation,fishery…) and between the Danube and Black Sea

● Put in place management plans considering the needs of migratory fish forthese habitats and ensure necessary adjustments of legal instruments (e.g.updating Annex II of the Habitats directive (species list) according to new dataavailable, especially with regard to the sturgeon species

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● Allocate appropriate resources to continue identification of habitats of keyimportance for migratory fish and to monitor progress;

● Ensure better legal solutions to protect key habitats and integrate the concept ofthe ecological corridor as an integral unit of connectivity, habitats andpopulations in the sectorial policies and environmental legislation

Description • Aquatic habitat protectionand restoration are important measures atspecific locations and are worth significantinvestments in order to preserve or returnthem for use by migratory fish species.These efforts include specific interventionsto improve water quality or the natural pat-terns of flow necessary for ecosystemhealth; most importantly, physical restora-tion of freshwater habitats (barrier removal,bank stabilisation, re-establishment of chan-nel morphology in a stream, wetland restor-ation etc); and also more traditional conser-vation tactics where land (or water) isplaced under a “protected” status. The chal-lenge with these Types of Measures is pur-suing them at a scale of significance.

Sometimes restoration to an original state isnot possible and all that can be achieved issome level of mitigation (i.e. remediation orrehabilitation in the above sense). Providedthis restores at least some ecosystem ser-vices and reverses biodiversity loss, thensuch remediation or rehabilitation can beviewed as a positive intervention (Geist &Hawkins 2016).

Habitat protection and restoration shouldbe considered together. To achieve a func-tional ecological corridor for migratory fishand based on economic considerations, ex-isting natural habitat preservation shouldbe given first priority, followed by key hab-itat restoration.


2.1. Habitats to be protected and restoredhave been identified

2.2. A basin-wide harmonised methodologyfor prioritising protection and restorationmeasures has been developed

2.3. Feasibility studies have been performedand solutions identified according to selec-ted species requirements

2.4. All necessary permits for restorationhave been obtained

2.5. Solutions for habitat restoration are be-ing implemented

2.6. Effects of restoration measures are be-ing monitored and measures adapted, if ne-cessary

2.7. A common database on protected/ re-stored habitat has been created, is regularlyupdated and maintained

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The Pan-European Action Plan for Sturgeons (PAN-EUAP) - Objective 3:Sturgeon habitats are protected and restored in key rivers.

EU-SDR-Action Plan – PA 4 – Water quality: Action 1: Hazardous & emergingsubstances, Action 2: Waste water, Action 3: Water & agriculture, Action 5:Migratory fish, Action 6: Climate change.

EU-SDR-Action Plan – PA 6 – Biodiversity and landscapes, quality of air andsoils: Action 3: Develop and/or implement conservation action plans and/ormanagement plans for endangered umbrella species of the Danube Region.

DRBMP-update 2021, Joint Program of Measures, Morphological Alterations

links to…

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Develop, promote and implement green infrastructure forflood management and nature-based solutions fornavigationToM 3

Target • Ensure the protection and enhancement of nature and natural processes.Negative ecological effects of future navigation and flood protection projects on na-tional and international levels are already taken into account in the planningphases and are minimised to the extent possible.

Rationale • Green infrastructure promotes using non-structural methods to ensuree.g. flood management and navigation and promotes using the integration of nat-ural and nature-based methods. MEASURES did not deal specifically with the neg-ative effects of future navigation and flood management. Nonetheless, an analysisof existing infrastructure projects has not only shown their negative ecologicaleffects but also that ecological requirements are not sufficiently addressed in thedifferent planning steps.

Principal addressees • Competent authorities and institutions in water manage-ment, flood protection, navigation


● Establish close cooperation and ensure involvement of migratory fish scientistsin future navigation and flood protection projects at the early planning phase

● Adjust technical solutions for implemented navigation projects that impactproper conditions for eCOR and did not yield substantial benefits fornavigation

● Ensure compliance of projects with the Espoo Convention (Convention onEnvironmental Impact Assessment in a Transboundary Context) in order toassess the environmental impact of certain activities that are likely to have asignificant adverse environmental impact across boundaries (navigation, sandmining, dredging).

● Perform EIA in accordance to the national and European legislation and ensurean investor-independent EIA assessment

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Description • Green infrastructure devel-opment means using non-structural meth-ods to ensure flood management. This in-cludes land use zoning as a first step, fol-lowed by integrating natural and nature-based methods, combined with hard engin-eering if needed, to manage flood risk. Nat-ural and nature-based methods such as

opening floodplains, upstream reforesta-tion, green roofs on downstream urbanareas, and wetland restorations and man-agement can improve the function of – andreduce the overall costs associated with –conventional engineering. They also allowcommunities to reap the co-benefits the en-vironment can provide such as: cleaner wa-

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ter, reduced air temperatures and greenspace for human recreation while protectinglivelihoods such as agriculture and fishing.

In the case of navigation, promoting greeninfrastructure/nature-based solutionsshould be the basis of all discussions. Solu-tions for a better waterway could involve acombination of limited hard hydrostruc-tural works with wise sediment manage-ment, artificial islands, natural bank-rein-forcement, etc.

Of the eleven infrastructure projects thatwere reported during plans and policy pa-per analyses performed in MEASURES –either ongoing or planned along theDanube River – the majority is dedicated toassessing, adjusting/harmonising and im-proving the conditions for navigation. Thisis because navigation is seen as an environ-mentally friendly type of transport withlow carbon emission. In comparison, onlyfew projects relate to hydropower produc-tion or to flood risk mitigation and watersupply.


3.1. Flood risk areas and river sections hav-ing high priority for navigation ("bottle-necks") have been identified

3.2. Close cooperation with and involve-ment of migratory fish scientists already atan early stage in future flood risk and nav-igation projects has been established

3.3. Areas of intervention have been priorit-ised

3.4. Habitat and species that will be im-pacted have been identified

3.5. A common database of projects hasbeen created and is regularly updated andmaintained

3.6. Feasibility studies have been performedto identify solutions in accordance withhabitat and species requirements, also pre-serving environmental services

3.7. All necessary permits have been ob-tained and public consultations performed

3.8. Technical solutions have been imple-mented

3.9. Effects of measures are being monitoredand measures adapted, if necessary

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links to…The Pan-European Action Plan for Sturgeons (PAN-EUAP) - Objective 3:Sturgeon habitats are protected and restored in key rivers, and Objective 4:Sturgeon migration (up-and downstream) is secured or facilitated.


EU-SDR-Action Plan – PA 6 – Biodiversity and landscapes, quality of air andsoils: Action 5: Anchoring the concept of EU green infrastructure in theDanube Region.

DRBMP-update 2021, Joint Program of Measures, Future Infrastructure Pro-jects

Figure 7: Several available documents promote the need for green infrastructure in generaland on the Danube more specifically.

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Secure and support populations of sturgeon species andother migratory fish by ex-situ measuresToM 4

Target • Save populations from extinction. To support threatened and re-establishextinct fish populations by ex-situ measures until wild fish populations are suffi-ciently recovered. Currently, this applies especially to the native Danube sturgeonspecies.

Rationale • Endangered populations need protection in the wild, but sometimesalso supportive ex-situ measures to rebuild population structure by releasing ge-netically suitable individuals from controlled propagation.

International classifications of the conservation status list, among the five Danubesturgeon species, one as extinct (A. nudiventris), one as functionally extinct (A.gueldenstaedtii), two as critically endangered (A. stellatus, Huso huso) and one as en-dangered (A. ruthenus). Without living gene banks in ex-situ facilities, populationrecovery not possible. The only option to safeguard viable native populations ofthese species is ex-situ measures, undertaken until populations reach a viable level,migration routes are open and sufficient habitats are available.

Principal addressees • Competent authorities and institutions in nature and bio-diversity conservation; research institutions to ensure state-of-the-art implementa-tion


● Build state-of-the-art ex-situ facilities for Sterlet conservation stocking inAustria and Slovenia

● Build state-of-the-art ex-situ facilities for anadromous sturgeon species (A.stellatus, A. gueldenstaedtii, Huso huso) conservation stocking in Bulgaria,Romania and Serbia

● Establish twinning facilities for risk spreading

● Exchange animals (spawners, juveniles) as "genetic exchange"

● Identify the need for activities for Danube Salmon, esp. in the middle Danubeand several tributaries such as the Mura River

In order to support the implementation of these priorities

● Ensure the necessary funds

● Ensure information exchange, capacity building and harmonisation ofmethodologies

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● Ensure international/ transnational synchronisation and coordination ofactivities

Description • Apopulation status below acertain threshold will not allow for recoveryon its own and inevitably lead to extinction.Such populations need protection in thewild, but also supportive programmes forrebuilding population structure by releasinggenetically suitable individuals that are fitfor survival under natural conditions andstem from controlled propagation in spe-cialised facilities. This is commonly knownas ex-situ measures or conservationaquaculture.

Many fish species are threatened by habitatdegradation and over-exploitation. At-tempts have often been made to com-pensate population deficits and/ or associ-ated fishery takes by rearing fish in hatcher-ies and releasing them into the wild, com-monly known as "stocking". Such releaseshave been reviewed critically in recent yearsbecause many of these activities did notyield the desired success or even had negat-ive effects on populations. Certain fish andespecially sturgeon populations, in contrast,would have been lost without human inter-vention and appropriate conservation meas-ures, also involving the reproduction ofbroodstock in captivity.

The successful use of controlled propaga-tion for the conservation of fish strongly de-pends on how well hatchery-reared animalscan adapt to natural habitat conditions. Animportant issue is how well hatchery opera-tions can preserve the genetic identity anddiversity as well as all other key attributesof the natural populations.

Ex-situ measures consist of establishingbroodstock from endangered populations incaptivity and their reproduction under(near-)natural environmental conditions.The goal is to release juveniles that are fit

for survival in the wild. They thereforework in accordance with the life-cycle of thepopulations, ensuring the feasibility ofmeasures with regard to a functioningaquatic ecology and ecosystem health.

Such measures are intended to "buy time" toensure the successful implementation of in-situ improvements like habitat protectionand restoration. Nonetheless, such recurrentintroductions of individuals from a captiveenvironment into natural populations har-bours the threat of altering the gene pooland detrimentally affecting the population.Accordingly, one of the most importantaims of ex-situ measures is to maintain andprotect the genetic identity and diversity, aswell as the morphological and behaviouralcharacteristics, of the respective populationsin both captivity and the wild.

This clearly distinguishes ex-situ pro-grammes from introductions in areaswithout native populations, from economic-ally boosting a fishery by releasing juven-iles, as well as from commercial hatcheryoperations that produce fish and fishproducts for human consumption.

The different terms used for ex-situ opera-tions include "conservation stocking", "con-servation breeding", "conservation hatch-ery", "conservation aquaculture", "captivebreeding" or simply "hatchery". The latter isoften misleading because ex-situ measuresgo beyond the concept of merely producinglarge quantities of fertilised eggs and lettingthem hatch. Nonetheless, these terms basic-ally have the same meaning if used in thecontext of sustainable conservation meas-ures for endangered fish populations.

The life-cycle of the respective populationsin the wild defines the conditions of ex-situ

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operations and the underlying principlesfor the conservation of migratory fish ingeneral. This means that ex-situ measuresare also closely linked to other conservationactivities such as habitat protection and res-toration, as well as restoring continuity atmigration barriers. As such, these measureshave to be well coordinated and synchron-ised.

Figure 8 demonstrates the main differencesbetween ex-situ operations and aquaculturefor human consumption using the exampleof sturgeons. The only common feature ofthese two different approaches is adult stur-geon broodstock being reproduced in a cap-tive environment. Note, however, thatbroodstock and captive environments differgreatly. Experience from other watershedsand populations has also shown that thesetwo concepts cannot be consolidated for theaim of conservation of endangered popula-tions.


4.1. Relevant species and populations of mi-gratory fish in need of ex-situ measures/programmes to prevent extinction have

been identified (addressing all migratoryspecies other than the extinct/critically en-dangered sturgeons, which are clearly inneed)

4.2. Ex-situ facilities and procedures forconducting ex-situ programmes have beenestablished

4.3. Genetically suitable broodstock hasbeen established, secured and is maintainedunder conditions that minimise negativeimpacts on wild populations (e.g. collectionand raising of juveniles and captive indi-viduals)

4.4. A common database on broodstock andex-situ operations and programmes for allstakeholders involved has been established,is regularly updated and maintained

4.5. Ex-situ operations are being conductedand juveniles released for rebuilding popu-lations in the wild

4.6. Ex-situ operations are monitored andadjusted regularly to adapt to changes andto accommodate progress in knowledge andexpertise

The Pan-European Action Plan for Sturgeons (PAN-EUAP) - Objective 2:Sturgeon population structure is actively supported to reverse the decline.


EU-SDR-Action Plan – PA 6 – Biodiversity and landscapes, quality of air andsoils: Action 3: Develop and/or implement conservation action plans and/ormanagement plans for endangered umbrella species of the Danube Region

links to…

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Figure 8: Differences between ex-situ measures and commercial aquaculture based on stur‐geons as an example (from Reinartz 2015).

Figure 9: Handling of a large sturgeon spawner in an ex-situ facility (Photo: Ralf Reinartz).

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Monitor connectivity, habitats and migratory fishpopulationsToM 5

Target • Ensure knowledge-based management of populations and habitat. Regu-lar monitoring is secured via integration into the relevant management and policyplans. An important aspect is to secure the necessary funds to fill remaining know-ledge gaps, especially for potamodromous migratory fish habitats and populations,and to accompany and control the effects of the above-mentioned ToMs. Monitor-ing of migratory fish provides evidence whether ecological corridors function andwhether fish migration aids function.

Rationale • Research and monitoring of populations and habitat is the basic pre-requisite for any kind of population and habitat management. MEASURES has de-livered new knowledge on potential and actual sturgeon habitats, but the involvedfish ecology experts have underlined still existing knowledge gaps.

Principal addressees • Competent national and international authorities and insti-tutions in water management, nature and biodiversity conservation, fishery, re-search


● Include monitoring of migratory fish into the scope of ICPDR’s Transnationalmonitoring and devote a separate section of the “TMNM Yearbook” tomigratory fish

● Ensure that fish migration aids at key bottlenecks for the entire Danube Basin(e.g. Iron Gates, Gabčikovo) as well as at the regional level are subject to regularor even continuous function controls. This is necessary to demonstrate that fishmigration aids work properly and that ecological corridors and measures taken(such as supporting stocking efforts) deliver what they promise. This approachalso provides first indications that populations of migratory fish are in place.

● Monitor habitats and populations of anadromous sturgeon in the lower Danubeand Black Sea

● Monitor habitats and populations of sterlet and in the upper and middleDanube and its tributaries

● Prepare pilot activities to e.g. assess potential habitats for reintroduction ofmigratory species in Hungary and Slovakia after restoring river continuity atthe Iron Gate

● Develop and implement a migratory fish monitoring methodology in all DRBcountries as part of the existing Joint Danube Survey

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In order to support the implementation of these priorities

● Mandate a working group to design a Danube-wide network of monitoringsites and a monitoring programme tailored to migratory fish (building onmonitoring of fish already in place to meet requirements of EU WaterFramework Directive and nature legislation)

● Ensure the necessary funds

● Ensure information exchange and awareness raising, capacity building,harmonisation of methodologies

● Ensure international/ transnational synchronisation and coordination ofactivities

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Description • Fish populations need habit-at: the inherent habitat use by populationsensures the completion of the life-cycle andsurvival of the species. This makes the mon-itoring of populations, important life stagesand their habitat crucial for delivering im-portant information on the state of popula-tions, habitat use and life-cycle-habitat. Thisis the basic prerequisite for any kind of in-tervention and management, i.e. the devel-opment and implementation of conserva-tion measures. It creates the up-to-date pop-ulation and habitat knowledge necessaryfor decision-making.

The management and conservation of fishpopulations and their habitat requires de-tailed knowledge on the population statusand its habitat resources. Equally importantare the detection of changes within this sys-tem, the identification of the underlyingcauses and impacts, as well as the power toconduct remediation actions if andwhenever necessary.

Population and habitat assessments lay thefoundation for population monitoring. Incontrast to single or recurring assessments,however, monitoring is designed as a sys-tematic continuous or repeated observation,measurement and evaluation of fish popu-lations and habitat parameters or indices,

according to predefined goals. This meansthat a monitoring programme must possessstrong analytical or diagnostic power to 1)enable early warning of changes within themonitored system, calling for early controlof the effectiveness of measures, activitiesand remedial actions, and to 2)prevent pos-sible future damage.

For migratory fish populations and theirhabitat, often encompassing internationalwaters and crossing borders, such activitieshave to be planned mutually, synchronisedand then implemented by all range coun-tries using a jointly adopted methodology.

Amonitoring programme is specific foreach population, follows the scientific state-of-the art as well legal standards requiredby e.g. conservation policy, and consists ofseveral main components that need to bedeveloped. The generalmonitoring object-ives are to assess the current state and todetect changes in the monitored system.Further objectives concern the desired preci-sion, confidence, spatial resolution, timescale and identification of causes of detec-ted changes. Details are provided in Figure10.

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5.1. Relevant species, populations and hab-itat needs have been identified based onconservation status and distribution todefine target species and habitat for all fur-ther measures

5.2. Habitat has been identified and de-scribed as both location and timing of hab-itat use, as well as the necessary physico-chemical and ecological conditions and re-sources

5.3. A common database on populationsand habitat has been established, is updatedand maintained regularly, open for allstakeholders involved

5.4. Monitoring procedures and pro-grammes for populations and habitat havebeen developed

5.5. Populations are monitored in sub-sequent assessments of important develop-mental stages during the life cycle, and pop-ulation changes and trends are being docu-mented

5.6. Habitat and its functionality in support-ing habitat use is being monitored

5.7. Monitoring methodologies have beenstandardised and harmonised within thedistribution area of the species

5.8. Measures for population and habitatprotection and restoration are carried outbased on all of the above

Figure 10: Scheme of a comprehensive monitoring programme.

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Figure 11: The ecological corridor of the Danube in Vienna. Braided blue structures indic‐ate historical pattern of temporal river stretches and furcations, creating a dense and di‐verse pattern of river flow and habitat for a multitude of fish species (from Hohensinner2020).

The Pan-European Action Plan for Sturgeons (PAN-EUAP) - Objective 5:Timely and continuous detection of population sizes and changes in remain-ing wild stocks

EU-SDR-Action Plan – PA 4 – Water quality: Action 5: Migratory fish


links to…

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Elaborate comprehensive National Activity Plans forMigratory Fish SpeciesToM 6

Target • Ensure applicability of the Strategy also on the national level. Developinga comprehensive set of activities, going beyond the technical foci of the MEAS-URES project.

Rationale • National Activity Plans for Migratory Fish Species (NAP-MFS) ensureconsistent targets, activities and implementation on the national scale. They allowaccounting for local and regional specifics as well as for international and basin-wide targets and framework conditions.

NAP-MFS should be built based on the MEASURES Strategy. In MEASURES part-ner countries, local networks can initiate the NAP-MFS. MEASURES has focusedon habitat identification, genetic analysis of sturgeons and ex-situ propagation ofsturgeons, national network building, and analyses of management and policyplans. Many topics were not addressed, but it should be ensured that they are dealtwith and integrated into consistent and comprehensive plans in the future.

Principal addressees • Competent authorities and institutions in water manage-ment, nature and biodiversity conservation, fishery, agriculture and other stake-holders according to stakeholder analyses on the national level.


● Screen ToMs of this Strategy and the national activities as mentioned in theannex and identify further priorities not addressed in MEASURES

● Establish opportunities for regular transnational exchange on development andstatus of NAP-MFS, necessary updates, etc.

● Seek synergies with existing Action Plans and solve conflicts with otherprojects, initiatives and policies

Description • Restoring the ecological cor-ridor as well as protecting and enhancingmigratory fish populations is a complextask. Beside gaps in ecological knowledgeof fish populations and habitats, it requiresdefining ecological targets, developingmeasures to reach those targets and imple-menting those measures. In addition, natureconservation and restoration efforts mustaccount for the framework conditions inwhich ecological decisions and activities areembedded. For migratory fish of the

Danube and its tributaries, multilateral ex-change and harmonisation are necessary.Those stakeholder needs whose targets op-pose the ecological ones must be dealt withand (best) compromise solutions must befound in which ecological impacts are min-imised.

In order to ensure that the complexity of mi-gratory fish conservation is fully addressed,National Activity Plans for Migratory FishSpecies (NAP-MFS) should be developed.

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NAP-MFS ensure consistent targets, activit-ies and implementation on the nationalscale. They help account for local and re-gional specifics as well as for internationaland basin-wide targets and framework con-ditions.

NAP-MFS shall be developed based on allavailable data on the migratory fish speciesand populations in question. Action Plansfor biodiversity conservation typically in-clude inventories of biological informationfor selected species or habitats, an assess-ment of the conservation status of specieswithin specified ecosystems, targets for con-servation and restoration, as well asbudgets, timelines and institutional partner-ships for implementation. Groves et al.(2002) have suggested a seven-step pro-gramme for Conservation Action Planning,which can be also be considered as an ex-emplary approach for migratory fish spe-cies: (1) identify conservation targets, (2)collect information and identify informationgaps, (3) establish conservation goals, (4) as-sess existing conservation areas, (5) evalu-ate the ability of conservation targets to per-sist, (6) assemble a portfolio of conservationareas and (7) identify priority conservationareas.

The NAP-MFS based on this MEASURESStrategy document shall subsequently de-scribe the targets with respect to migratoryfish, the main measures and activities neces-sary to reach these targets, as well as theprogramme to monitor the effects of activit-

ies as well as to monitor the development offish species and populations along with in-dicators of success. Important componentsinclude a clear time-schedule as well as alist of stakeholders who were involved indefining targets and measures and/or whoare concerned with implementing the meas-ures. In MEASURES partner countries, localnetworks can initiate the NAP-MFS (seeType of Measure 7).


6.1. The preparation of national activityplans has been initiated

6.2. Support and necessary funding for thepreparation of activity plans has been ob-tained from national authorities or othersources (e.g. European funds)

6.3. A (legal) governance framework for theecological corridor has been defined andsupport from national authorities has beenobtained

6.4. Basin-wide targets specified in thisStrategy have been adapted and detailed inaccordance with national specifics andstakeholder priorities

6.5. The implementation, monitoring andsuccess control of the NAP-MFS has beeninitiated

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Figure 12: In 2019, an Action Plan for river birds in the planned five-country Biosphere reserve “Mura-Drava-Danube” was published. Such Action Plans can serve as a guide for developing national activityplans for the Danube ecological corridor and migratory fish, but they can also offer synergies for jointconservation targets.

links to…The Pan-European Action Plan for Sturgeons (PAN-EUAP) – all objectives.

EU-SDR-Action Plan – PA 4 – Water quality: Action 5: Migratory fish, Action7: Tools


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Strengthen “Local Migratory Fish Networks”ToM 7Target • Create structures of expertise and responsibility. Further develop theMEASURES networks initiated on local and national levels as well as establish or-ganisational structures for ecological corridor and migratory fish conservation onthe national scale while simultaneously ensuring transnational exchange and har-monisation.

Rationale •Well-established Local Migratory Fish Networks ensure the imple-mentation of the NAP-MFS (see Type of Measure below). They can act as exchangeand cooperation platforms on a basin-wide or even European scale. They also al-low a timely reaction if framework conditions change. Organisational structures topromote and ensure the conservation and restoration of the Danube ecological cor-ridor are still missing. However, well-established organisational structures offermany advantages and should therefore be pursued. For example, they compile ex-isting expert knowledge and make this easily available to individual networkmembers, they offer fast communication and short reaction times, or they help in-crease awareness.

Principal addressees • Competent authorities and institutions on the internationaland national level as well as NGOs, associations, research institutions and theprivate sector in water management, flood protection, nature and biodiversity con-servation, research, fishery, navigation, hydropower


● Identify responsible bodies and demand commitment from them to supportimplementing measures and activities of this Strategy by including relevantaspects into management and policy plans (e.g. National River ManagementPlans)

● Further elaborate the tasks of the LMFNs and the contents of the NAP-MSF

● Identify and designate the relevant national actors/stakeholders/structures (ifpresent) and assign specific tasks to as well as demand commitment from them

● Identify relevant existing local and national networks to explore synergies andoptions for cooperation

● Ensure exchange of Local Migratory Fish Networks on a basin-wide scale

● Enhance coordination with authorities competent for other sectors at nationaland international level

● Enhance cooperation between the Danube Region and Black Sea Region,focusing on all issues of relevance for migratory fish

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● Identify and verify issues of transnational concern

● Identify funding sources and ensure funding

● Abasis for Local Migratory Fish Networks has been established in mostMEASURES partner countries. In case new LMFNs should be established, amapping of stakeholders should be the starting point.

Description • Local Migratory Fish Net-work (LMFN) in the context of this Strategyrelates to a fixed group of stakeholders.They will communicate and meet on a regu-lar basis to implement one or several spe-cific measures and activities with regard tothe ecological corridor for migratory fishes.The Strategy and the Types of Measures canserve as a framework. LMFNs are respons-ible for developing the National ActivityPlans for Migratory Fish Species (NAP-MFS, see Type of Measure 2) and for initiat-ing and controlling implementation. Theycan be formed by a core group of organisa-tions and entities that are primarily in-volved in nature conservation and restora-tion. At the same time, they strive to informa wider group of concerned stakeholders orto involve such groups in prioritising activ-ities or decision making. It is recommendedthat LMFNs define rules and guidelines bywhich to function. Further, they delegatemembers to transnational and internationalnetworks or meetings and report and ex-change there about local and national activ-ities to improve the functioning of the eco-logical corridor. Migratory Fish Networksallow a timely reaction if framework condi-tions change, provided NAP-MFS haveclear and traceable descriptions on how toobserve such framework conditions.

In the constitutive phase, systematic map-ping of stakeholders by initiator(s) is recom-mended. This is designed to ensure the con-sideration of all relevant legal and adminis-trative institutions, important associations,networks and actors who are concerned

with biodiversity and conservation as wellas with the restoration of the Danube ecolo-gical corridor, especially with the respectiveneeds of migratory fish and their habitats.Parallel to stakeholder mapping, an invest-igation of relevant ongoing processes andframework conditions (legal framework,administrative responsibilities) is recom-mended. Mapping of existing associationsand networks will also allow connectingLMFN to existing structures to reduce theadditional workload to the extent possible.

Apart from activities on the national and re-gional scale, Local Migratory Species Net-works act as exchange and cooperationplatforms on a basin-wide or evenEuropean scale. Links to existing organisa-tions as well as local, national and basin-wide networks concerned with biodiversityand nature conservation and river restora-tion should be established. On the transna-tional scale, the DSTF, the EU-SDR (in par-ticular PA6) and the ICPDR are of particularinterest to facilitate basin-wide exchange aswell as to consider closely related targets.


7.1. Local Migratory Fish Networks(LMFNs) have been initiated or existingones stabilised

7.2. Targets and tasks of local networks (in-cluding training and capacity building forrelevant stakeholders) have been defined

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The Pan-European Action Plan for Sturgeons (PAN-EUAP) – all objectives.

EU-SDR-Action Plan – PA 4 – Water quality: Action 5: Migratory fish, Action7: Tools

EU-SDR-Action Plan – PA 6 – Biodiversity and landscapes, quality of air andsoils: Action 2: Build capacities of national and local authorities, non-govern-mental organisations, expert and scientific community in environment-re-lated matters, Action 3: Develop and/or implement conservation actionplans and/or management plans for endangered umbrella species of theDanube Region

links to…

7.3. Scientific, institutional and financialsupport has been secured

7.4. Gaps and weaknesses in the legal andinstitutional framework have been accoun-ted for

7.5. Exchange on the basin-wide scaleamong LMFNs (e.g. annual meetings) aswell as with relevant organisations such asICPDR, DSTF and EU-SDR (in particular PA6) is established and ensured

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Improve public participation and support for LocalMigratory Fish NetworksToM 8

Target • Ensure public, stakeholder and political support. To create the frameworkfor public debate for decisions and projects in order to raise their acceptance in so-ciety

Rationale • Public participation is a process that directly engages the public in de-cision-making and gives full consideration to public input in making such de-cisions. The more complex the subject of debate is, the greater the variety of in-terests that will emerge from different organisations: research institutes, universit-ies, NGOs, governmental authorities, local authorities etc. Communication and fa-cilitation skills then become key elements to build relationships and obtain appro-priate data and information to develop realistic plans and projects. The MEAS-URES project developed an External communication strategy that can be adaptedand improved according to different needs because the communication strategydoes not cover all aspects of the eCOR conservation

Principal addressees • Competent authorities and institutions involved in watermanagement, nature conservation and fisheries management on the basin and na-tional level, NGOs, organisations and associations, projects beneficiaries


● Build water democracy by establishing local water councils

● Better involve stakeholders and public in decisions regarding rivermanagement planning, especially on national levels; the ICPDR Publicconsultation processes can serve as examples

● Build capacity among all levels of stakeholders, including raising awareness ofthe general public, regarding the requirements and management options forfish conservation (Slovenia)

● Initiate harmonisation of multi-national plans for shared river catchments

● Initiate harmonisation of fishing and the legislation of other sectors with crossborder influence

Description • The Aarhus Convention andits Protocol on PRTRs empower people withthe rights to access information, participatein decision-making in environmental mat-ters and to seek justice. Public participationseeks and facilitates the involvement ofthose potentially affected by or interested in

a decision. It is a process – not a singleevent – and should be planned from theearly stages of management plans or projectdevelopment. At the same time, the chal-lenge of ensuring an adequate and equit-able treatment of participants in consulta-tion processes should not be underestim-

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ated. The more complex the subject of de-bate is, the greater the variety of intereststhat will emerge from the different organ-isations: research institutes, universities,NGOs, governmental authorities, local au-thorities, fishers, etc. This means that com-munication and facilitation skills becomekey elements to build relationships and ob-tain appropriate data and information todevelop realistic plans and projects.

Public participation is not simply a nice orancillary thing to do: it actually results inbetter outcomes and better governance.When done appropriately, public participa-tion will yield two significant benefits:

● Decision makers and projectbeneficiaries will make better and moreeasily implementable decisions thatreflect public interests and values andare better understood by the public.

● Communities develop a long-termcapacity to solve and managechallenging social issues, oftenovercoming longstanding differencesand misunderstandings.

The eight local networks for migratory fishconservation from the Danube countries in-volved in the MEASURES project have beenidentified by using a complex matrix. Thatmatrix takes into consideration general in-formation, the spatial scale of their impact,category, area of interest, what we wantfrom them, past cooperation, contributionto the project including conflicting interests,as well as contact persons and their re-sponsibility in the institution. The networkshave a complex structure, wide representa-tion and potential members have been in-volved in the Strategy development duringthree rounds of national workshops and thefinal conference.


8.1. Social and political scientists are in-volved in LMFNs, especially experts in gov-ernance as well as experts in fosteringstakeholder and policy dialogue

8.2. A stakeholder analysis has been per-formed

8.3. A communication and involvementstrategy which accounts for different typesof stakeholders as well as for the generalpublic has been developed. Input and feed-back from and dialogue with these groupshas been ensured

8.4. The period allocated for the consulta-tion has been established

8.5. Stakeholder meetings and round tablesfocussing on interactive exchange betweenLMFNs and stakeholders are being organ-ised and conducted

8.6. Results of meetings are being recordedand kept available for all involved stake-holders

8.7. Public consultation is being capitalisedon. Decision makers are informed about theresults of consultations. As a first step, con-crete measures identified within the MEAS-URES project have been submitted toICPDR and its consulting parties

8.8. Stakeholder input in public consultationprocesses is recognised and the consultationprocess results are being communicated tothe general public

8.9. Citizen Science and other awareness-raising activities among the general publicare being promoted

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links to…The Pan-European Action Plan for Sturgeons (PAN-EUAP) – Objective 8:Sturgeons serve as flagship species for healthy river ecosystems. Supportfrom the public, political actors, authorities and relevant stakeholders forconservation measures has increased

EU-SDR-Action Plan – PA 4 – Water quality: Action 5: Migratory fish


8.10. Guidance documents for municipalit-ies and other target groups on the availablegreen solutions, NBS and ecosystem-basedmanagement are being developed and dis-seminated

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The successful implementation of thisStrategy depends on different competentauthorities and institutions responsible forprotecting, restoring and maintaining anecological corridor. As no single authorityor institution – neither on the basin nor onnational levels – is responsible for all threeelements of the ecological corridor, coordin-ated actions are needed.

Principal addressees are the relevant basin-wide (esp. ICPDR, coordinators and mem-bers of EU-SDR PA 6, etc.) and national au-thorities and institutions from the sectors ofriver basin management as well as biod-iversity and nature protection. Water man-agement institutions concerned with devel-oping, updating and implementing theRiver Basin Management Plans must strivefor physical river continuity and habitatconditions that allow achieving good ecolo-gical status or good ecological potential.

The competent authority for transboundarywater management in the Danube Basin isthe ICPDR. It has the powers necessary tomandate Danube states to take measures toestablish such corridors, including bothcontinuity measures and habitat measures.

Conservation of migratory fish is at thecrossroads between water management andmanagement of nature and biodiversity.While nature protection authorities and in-stitutions take certain responsibilities forhabitat protection and restoration, their roleis often less prominent than water manage-ment institutions. This raises the need toclarify the roles and responsibilities of na-tional nature and water management.

There are currently no legal obligations tosustain critically endangered fish popula-tions by means of conservation hatcheries(i.e. ex-situ facilities). Given their nature

06 Strategy implementation

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Figure 13: As a starting point, only few stakeholder groups might be involved in implement‐ing the Strategy for ecological corridor conservation on the national but also on the basin-level. It is envisioned that, over time, all relevant stakeholder groups are involved (right sideof figure).

and purpose, as well as the legal instru-ments they have, it is proposed that natureprotection authorities in the EU and con-cerned Danube States should take respons-ibility to support, initiate or establish suchex-situ facilities.

There are sectors beyond the above-men-tioned that exert significant adverse effectson continuity, habitats and fish populations.Such adverse effects will increase in the fu-ture, e.g. for navigation, hydropower orsand/gravel mining. There is a need to en-sure that policies and their implementationeffectively support the recovery and conser-vation of the Danube ecological corridor.The EU, the ICPDR and the EU-SDR (PA 06)should take the lead in developing this sup-port (in particular for sectors with trans-boundary consequences such as energy, cli-mate and inland waterway transport) witha view to implementation by the relevantcompetent national authorities.

The recommendation is to initiate and es-tablish organisational structures for suchcross-sectoral exchange on basin-wide and

national levels. These can build on the LocalMigratory Fish Networks initiated in thecountries represented in the MEASURESproject. There is no coherent situation inthese countries due to national differencesin challenges related to the ecological cor-ridor and migratory fish, but also due todifferences in already established commu-nication between stakeholders from differ-ent sectors. Sometimes, the initial LMFNscomprise only a smaller group of stakehold-ers focussing on nature conservation andbiodiversity; sometimes, more diversestakeholder groups have already agreed tosupport and actively engage in implement-ing this Strategy.

As detailed in Chapter 5, ToM LMFN, fur-ther extending such networks towards aninternational level is urgently needed to en-sure a basin-wide exchange, agreements, co-ordination and harmonisation of measuresand activities.

6.1 Indicators and monitoring ofsuccess

Monitoring of the success is an importantelement of implementing this Strategy. Itshould be done on two levels, i.e. on thelevel of milestones as well as on the level ofmeasures and activities as formulated in theNAP-MFS.

The following list of indicators follows thetimeline as suggested for the ToMs, themilestones (see Chapter 2) and implementa-tion steps. There are two types of indicators.Some are binary (yes or no), while othersare quantitative and can be measured innumbers. Especially for qualitative indicat-ors, further specification should beprovided. For example, for the indicator“Relevant deficits in habitat, populationsand continuity identified” a target area

should be given. No timing is considered,but timeframes should be defined by thedifferent LNMFs on the country level. Wealso recommend to define targets to bereached within this time period.

Depending on the more specific activities asdefined e.g. in the NAP-MFS, additional in-dicators can be defined. Importantly, indic-ators must be clearly measurable. For thoseindicators that cannot be quantitativelymeasured or for which a binary evaluationis not possible, the recommendation is toadd criteria which prove success.

Local Migratory Fish Networks can be re-sponsible for monitoring the indicators ofsuccess.

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Table 6: List of indicators to monitor the implementationof the measures and activities aiming at securing andrestoring the ecological corridor and migratory fish.

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IndicatorType ofmeasure-ment

Further specification

Relevant deficits in habitat, populations andcontinuity identified

Qual.(yes/no)

River or river section

Current (used) habitat, potential habitat (e.g.for reintroductions), habitat conditions/ re‐sources and pressures identified and de‐scribed

Qual.(yes/no)

River or river section

National and international relevance of meas‐ures and activities identified

Qual.(yes/no)

Not relevant

National Activity Plans completed, includingconservation and restoration of populations,habitat and physical continuity

Qual.(yes/no)

Not relevant

No. of projects developed Number Define target number

Sufficient funding secured Qual.(yes/no)

Define for which activities funding isneeded

No. of projects implemented Number Define target number

No. of habitats for which formal protectionstatus has been achieved

Number Define target number

No. of restoration projects ongoing or com‐pleted


No. of monitoring programmes in place Number Define target number and specify whichkind of monitoring (e.g. habitat, fish popu‐lations, migration), define river/river section

No. of physical continuity conserved and re‐stored


No. of ex-situ programmes running Number Define target number and for which fishspecies

Population targets for monitoring and manage‐ment defined

Qual.(yes/no)

Define e.g. minimum number for abund‐ance or biomass

No. of policy and management plans intowhich Types of Measures specified in thisStrategy were integrated


Overall number of activities implemented orapplied in practice


Continuous length of ecological corridor result‐ing from Strategy application within policy andmanagement

Number Define target length

Challenges

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ks

Even the best-planned strategy can en-counter unexpected problems. These can berelated to human, operational, procedural,financial, technical, natural and political as-pects that potentially affect meeting the tar-gets and objectives of the Strategy. Not allrisks are negative. Some events or condi-tions can be helpful and, when they occur,these turn into opportunities.

The present Strategy covers a wide territoryas well as countries with different culturesand different accessibility to resources. Ac-cordingly, 10 potential evaluations of differ-ent kinds of risks have been made at the na-tional level in terms of the probability of oc-currence. These have been grouped as high,medium and low risks. The overview belowsummarises these national evaluations onthe basin scale.

The present document has no legal weightand depends heavily on promotion by the

contributors to keep it alive and on the will-ingness of the responsible authorities totake up and implement the Strategy. As con-sequence, the highest risks are associatedwith human, financial and procedural cat-egories such as low or no interest of thestakeholders for the Strategy, changes ofkey persons among stakeholders includ-ing project partners, insufficient or nofunds for measures implementation andimportant delays in the implementationschedule. Establishing viable stakeholdernetworks requires sincere debates, an un-derstanding of all points of view, trust andtime. Some countries have been able tobuild on older relationships, but in manycases networks are merely at a very earlyphase. In the latter cases – given that thetime to built such networks during theMEASURES project was short – the interestin the Strategy measures could not be suffi-ciently strengthened. In both cases, toomany changes of involved people can

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weaken the network. Preserving but espe-cially restoring longitudinal river continuityoften requires large-scale and expensiveprojects, which must go through complexprocedures that can sometimes causelengthy delays. Ensuring the necessaryfunds for measures implementation can be-came a challenge if they fail to be integratedin policy and management plans accompan-ied by proper funding programmes. In thecoming years, however, the available fundswill be greatly influenced by the evolutionof the Covid-19 pandemic and the need foreconomic recovery. At the same time, theywill also be linked to a more sustainable de-velopment, offering new funding opportun-ities for biodiversity.

Medium risk covers limited or no access tonew data, absence of a focal point in eachcountry, high costs and lack of technicalsolutions to implement the Strategy meas-ures, as well as weather, natural disastersor disease. In some countries the data areshared by several owners or there is no cul-ture of transparency; such cases pose a chal-lenge to keep the MEASURES InformationSystem MIS properly updated. Active focalpoints should coordinate the Strategy im-plementation at the national level and keepin touch with initiatives from other coun-tries. Since no funds are available to hiresuch a designated person in each country,the focal point should assume this role vol-untarily or that role should be assumed byresponsible authorities.

Preserving but especially restoring longit-udinal river continuity often requires large-scale engineering solutions that consumetechnology, human resources and funds.Many state-of-the-art technologies are avail-able, and EU funds used on the basis ofcomplementarity can reduce the risks ofhigh costs and lack of technical solutions.When it comes to dams, however, solutionsand money can became constraints.

Weather, natural disasters or disease aredifficult to predict. Nonetheless, as climatechange progresses, we can expect to increas-ingly face floods, droughts, major vegeta-tion fires etc..

Low risk is seen in changes in nationalgovernmental policies. This is becausemain national government policies are re-lated to EU policies and, as a result, no sig-nificant changes in policies are expected.Nonetheless, the prioritisation of policiescould vary according to the politicalchanges.

Unexpected aspects or conditions and theMEASURES project can or have alreadygeneratedmany opportunities. The MISdata base and project deliverables offercompiled expert experience and measuresrelevant for the whole Danube. Awarenessfor migratory fish and ecological corridorshas increased at the national level.

The framework established by the MEAS-URES project creates a starting point forproject proposal development and projectimplementation. This framework could mit-igate and buffer local threats and risks (e.g.natural, political) by spreading them overthe networks and larger areas.

Local networks facilitate quick and simpleaccess to expert information on migratoryfish and ecological corridors or other relatedfields. They also promote faster communic-ation and reaction along established tracks.As open structures, local networks can in-tegrate additional actors and fields of ex-pertise, communicate with other networksand institutions, and mitigate the negativeeffects of individual personnel fluctuationsor the drop-out of institutions as a whole.They can also function at low intensity(along the lines of existing expertise anddaily tasks), even without additional fund-ing apart from personnel resources, which

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are offered by institutions to delegate theiremployees to meetings etc.

Part of the measures set out in this Strategyfor the conservation of the ecological cor-ridor can benefit from funds based on oneof the priority objectives: the “restoration ofriver continuity” of the EU BiodiversityStrategy 2030.

In conclusion, certain risks can have a neg-ative impact on the good implementation ofthe Strategy, but the opportunities shouldnot be underestimated or lost.

The recommendation is to update theStrategy and action plans in 2027 at thelatest. This would enable following the revi-sion cycle of important management docu-ments such as the RBMPs. The coordinatorsof Local Migratory Fish Networks are slatedto meet once per year, and the necessity forand processes of an update shall be dis-cussed and decided then.

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9.1 Glossary

activity – in this document, part of a "Typeof measure"

adult – a fish after reaching maturity

alluvial – sediment deposited by rivers,floods and water in general

anadromous – fish which migrate up riversfrom the sea to spawn

barbel zone – European river zonation: low-land river stretches, retaining some charac-teristics of upland rivers such as a gentlegradient with moderate water flow andtemperature, good oxygen content and amixed substrate of silt and gravel. The Bar-bel (Barbus barbus) often is a dominating fishspecies.

benthi-insectivorous – fish or animals ingeneral feeding on bottom-dwelling organ-isms and insects and their larvae

biodiversity – the variety of plant and an-imal life in the world or in a particular hab-itat, a high or natural level of which is usu-ally considered to be important and desir-able, as it is associated with a higher stabil-ity, productivity and recovery potential of arespective ecosystem

biota – the animal and plant life of a partic-ular region, habitat, or geological period

broodstock – a group of mature fish usedfor breeding purposes

Carpathian Convention – the FrameworkConvention on the Protection and Sustain-able Development of the Carpathians

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CITES – Convention on International Tradein Endangered Species of Wild Fauna andFlora

coded wire tag – an animal tagging device,consisting of a magnetised stainless steelwire, most often used for identifyingbatches of fish

connectivity – in this document, the phys-ical or ecological connectedness of riverstretches, habitat and populations

conservation – saving and protecting a stillnatural or nature-like habitat and all of itscomponents

continuity – in this document, the uninter-rupted presence of life cycle- and habitatuse- supporting conditions, resources, hab-itat and populations

controlled propagation – (artificial) produc-tion of individuals of a species; in the con-text of this document, generally within amanaged environment, for the purpose ofsupplementing or augmenting wild popula-tions, or reintroduction to the wild to re-es-tablish populations

cyprinid – fish belonging to the family ofsoft-finned freshwater fishes including carpand minnows (Cyprinidae)

Danube Sturgeon Task Force – an initiativeestablished in January 2012 within theframework of the macro-regional EUStrategy for the Danube Region (EU-SDR)Priority Area 6 (Biodiversity)

DANUBEPARKS – a network of protectedareas from 9 countries

DANUBEPARKS connected – a project tobridge the Danube Protected Areas towardsa Danube Habitat Corridor

detriti-herbivorous – fish or animals in gen-eral feeding on dead organic material andplant material

diadromous – fish migrating between saltand fresh waters for spawning (see alsoanadromous)

ecological corridor – entity of a river catch-ment which comprises physical connectiv-ity, habitat connectivity as well as viablepopulations of fish or animals in general

endemic – a plant or animal native and re-stricted to a certain place or region

environmental niche – aka ecological niche:the match of a species to specific environ-mental conditions

Espoo Convention – Convention on Envir-onmental Impact Assessment in a Trans-boundary Context

estuarine – relating to an estuary, a partiallyenclosed coastal body of brackish waterwith one or more rivers or streams flowinginto it, and with a free connection to theopen sea

European Green Deal – a set of policy initi-atives by the European Commission withthe overarching aim of making Europe cli-mate neutral in 2050

eurythermal – fish or animals and plant ingeneral able to tolerate a wide range of tem-peratures

eurytopic – a plant or animal found in awide range of environments, and thuswidely distributed

ex-situ conservation – the preservation ofcomponents of biological diversity (e.g. an-imals) outside their natural habitats

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ex-situ measures – measures referring to ex-situ conservation

Fish Migration Foundation – a non-profitorganisation dedicated to the preservationand restoration of migratory fish speciesand free-flowing rivers around the world

fisheries (and their organisations) – activityof raising or harvesting fish and otheraquatic life

flagship species – a species chosen to raisesupport for biodiversity conservation in agiven place or social context; often specieswhich have high societal value or recogni-tion, such as sturgeons

flood protection – methods and activitiesused to reduce or prevent the detrimentaleffects of flood waters

floy external T-bar anchor tags – externalmechanical tag for fish

fluvial – referring to processes associatedwith rivers and streams

functionally extinct – the loss of a popula-tion's viability

gene-pool – the total genetic diversity foundwithin a population or a species

grayling zone – European river zonation:upland river stretches with a steep gradient,fast-flowing water, cool temperature andhard bottom substrates (rocks, gravel). Thefast flow rate causes turbulence whichkeeps the water well oxygenated. Fish spe-cies found in this zone usually lay adhesiveeggs that can stick to the substrate. TheEuropean grayling (Thymallus thymallus) of-ten is a dominating species.

Green Infrastructure – a strategicallyplanned network of natural and semi-nat-

ural areas with other environmental fea-tures designed and managed to deliver awide range of ecosystem services in bothrural and urban settings

habitat connectivity – (seasonal/discharge-dependent) connection of habitats which al-lows for movements of migratory fish forspawning, wintering, feeding, etc.

hydrological runoff regime – the distribu-tion of water runoff over time in a water-shed

hydropower – power (electricity) derivedfrom the energy of falling or fast-runningwater

insecti-piscivorous – fish or animals in gen-eral feeding on insects and their larvae aswell as on fishes

insectivorous – fish or animals in generalfeeding on insects and their larvae

in-situ conservation – the conservation ofecosystems and natural habitats and themaintenance and recovery of viable popula-tions of species in their natural surround-ings

Interreg-Danube Transnational Programme– a financing instrument of the EuropeanTerritorial Cooperation (ETC), better knownas Interreg, providing a framework for theimplementation of joint actions and policyexchanges between national, regional andlocal actors from different Member States.The Danube Transnational Programme(DTP) promotes economic, social and territ-orial cohesion in the Danube Regionthrough policy integration in selected fields.

juvenile – a young fish after losing larvaltraits and before becoming mature

key habitat – a habitat type that is essential

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for the completion of the life-cycle of a fishspecies

lacustrine – of or relating to lakes

LIFE project – project under the EU LIFEprogramme

limnopar – fish or animals in general whichreproduce in stagnant water

lithopelagophilic – fish or animals in gen-eral which spawn close to hard substrates,spawn drifts in the water column

lithophilic – fish or animals in generalwhich spawn on hard substrates (rocks,gravel)

littoral – referring to the shore of a waterbody

Local Migratory Fish Networks – in thisdocument, the basic units working to imple-ment the Strategy for ecological corridorconservation in the Danube catchment

Lower Danube – the Danube River betweenthe Black Sea and the Iron Gate gorge, in-cluding the delta

marine – of or relating to the sea or theplants and animals that live in the sea

Middle Danube – the Danube Riverbetween the Iron Gate gorge and the DevinGate (between Hainburg and Bratislava)

migratory – of or relating to migration

National Activity Plans for Migratory FishSpecies – in this document, plans by theLocal Migratory Fish Networks to imple-ment the Strategy for ecological corridorconservation in the Danube catchment orparts of it

navigation – the transport of people (pas-sengers) or goods (cargo) via waterways inthe context of this document

omnivorous – fish or animals in generalfeeding on a variety of food of both plantand animal origin

pelagic-neritic – fish or animals in generalspawning in the water column still reachedby sunlight

physical connectivity – longitudinal con-nection of river corridors which allowsmovement of migratory fish for spawning,wintering, feeding, etc.

phytophilic – fish or animals in generalspawning on plants

piscivorous – fish or animals in generalfeeding on fish

PIT tag – an internal tag for animals (apassive integrated transponder)

potamal – referring to the lower stretches ofa stream or river

potamodromous – fish moving and com-pleting the life-cycle in freshwater exclus-ively

Priority Area (PA) 4 (Water Quality) – oneof 12 priority areas within the EuropeanStrategy for the Danube Region

Priority Area (PA) 6 (Biodiversity andLandscapes, Quality of Air and Soils) – oneof 12 priority areas within the EuropeanStrategy for the Danube Region

rheopar – fish spawning in flowing water

rheophilic – fish preferring or living in flow-ing water

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rhithral – referring to the upper stretches ofa stream or river with fast-flowing, well-oxygenated water

riparian – relating to or situated on thebanks of a river

riverine – relating to or situated on a riveror riverbank

stagnophilic – fish or animals in generalpreferring to live in stagnant water

stenothermal – fish or animals in generalcapable of surviving over only a narrowrange of temperatures

Sturgeon 2020 – a strategy and programmefor the protection and rehabilitation of theDanube sturgeons by the Danube SturgeonTask Force

subadult – referring to a fish with adulttraits but not being mature

Type of Measure (ToM) – in this document,a category of measures identified in theMEASURES Strategy based on the coretasks of the project; each Type of Measuresconsists of specific activities

umbrella species – species selected for mak-ing conservation-related decisions, typicallybecause protecting these species indirectlyprotects the many other species that makeup the ecological community of its habitat

Upper Danube – the Danube River betweenits source and the Devin Gate (betweenHainburg and Bratislava)

viable populations – self-sustaining popula-tions of migratory fish which are able tomove along the river corridor and betweenhabitats to complete their life-cycles.

water management – the activity of plan-

ning, developing, distributing and man-aging the optimum use of water resources

9.2 Abbreviations and acronyms

BC – Bern Convention-Convention on theConservation of European Wildlife andNatural Habitats

BDS – EU-Strategy for Biodiversity 2030(BDS)

BOKU – Universität für Bodenkultur, Wien- University of Natural Resources and LifeSciences, Vienna

CBD – Convention on Biological Diversity(CBD)

CMS – Bonn Convention-Convention onthe Conservation of Migratory Species ofWild Animals

CWT – Coded Wire Tag

DDNI – Danube Delta National Institutefor research and development, Tulcea

DRB – Danube River Basin

DRBD – Danube River Basin District

DRBMP – Danube River Basin Manage-ment Plan

DSTF – Danube Sturgeon Task Force

DTP – Danube Transnational Programme

EA – Environmental Assessment

eCOR – Ecological Corridor

EIA – Environmental Impact Assessment

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ERDF – European Regional DevelopmentFund

Espoo Convention – Convention on Envir-onmental Impact Assessment in a Trans-boundary Context

EU-SDR – EU Strategy for the Danube Re-gion, a macro-regional strategy adopted bythe European Commission

FD – Flood Directive

HD – Habitat Directive

IAWB – Impact Assessment on Water Bod-ies, refers to the study “Assessing environ-mental Impact of Water Bodies” on the ap-plication of WFD art 4(7)

ICPDR – International Commission for theProtection of the Danube River

IHG – Institut für Hydrobiologie undGewässermanagement, BOKU, Wien - Insti-tute of Hydrobiology and Aquatic Ecosys-tem Management, BOKU, Vienna

IMFN – International Migratory Fish Net-work

IMSI – Institute for Multidisciplinary Re-search, University of Belgrade

IPA – Instrument for Pre-Accession Assist-ance, a programme and financial instru-ment for EU candidate countries or poten-tial candidate countries

IUCN – International Union for Conserva-tion of Nature

IUU Fishing – illegal, unreported and un-regulated fishing (e.g. poaching, bycatch)

JDS – Joint Danube Survey

KU – Karlovac University of Applied Sci-ences

LMFN – Local Migratory Fish Network

MEASURES project – “Managing andrestoring aquatic EcologicAl corridors formigratory fiSh species in the danUbe RivErbaSin”

MSFD – Marine Strategy Framework Dir-ective (MSFD)

N2000 – Natura 2000

NAIK-HAKI – NAIK - HalászatiKutatóintézet, Szarvas - Research Institutefor Fisheries and Aquaculture, Szarvas

NAP-MFS – National Activity Plan for Mi-gratory Fish Species

NBS – Nature-based Solutions

NGO – Non-Governmental Organisation

PAN-EU AP – Pan-European Action Planfor Sturgeons under the Bern Convention

RBMP – River Basin Management Plan

REVIVO – Institute for ichthyological andecological research, Slovenia

SEA – Strategic Environmental Assessment

STURGENE – ex-situ survey to preservesturgeon genetic diversity in the middleand lower Danube (STURGENE) - projectunder the EU-SDR START programme

ToM – Type of Measure

TRUNI – Trnavská univerzita v Trnave -Trnava University

WFD – EuropeanWater Framework Directive

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WSCS – World Sturgeon Conservation Soci-ety

WWF – World Wide Fund For Nature

WWF CEE – WWF Central and EasternEurope

9.3 MEASURES internaldocuments used

D 1.2.1 – 1.2.5, D 4.3.1 – Deliverables onworkshops in T1 and T4, deliverables onstakeholders and national nuclei

D 2.1.2 – Danube Migratory Fish HabitatManual

D 2.3.1 – Data of pilot habitat mapping

D 2.3.2 – Reports on joint migratory fishhabitat mapping pilot actions and testing ofmethodology

D 3.1.1 – Genetic conservation manual forex-situ Danube sturgeon live gene stocks tosupport the development of supportive re-stocking programmes and maintaining thegenetic connectivity

D 3.2.1 – Results of Sterlet broodstock col-lection and genetic analysis. Detailed list ofcollected broodstock (biometrical and ge-netic dataset) providing a genetic basis offurther restocking activities

D 3.2.2 – Restocking activities for Sterlet inspring and autumn 2019 including mediaevents, press releases, conferences and in-teraction with World Fish Migration Found-ation

D 3.3.1 – Restocking activity for Russiansturgeon in spring 2019 at the selected re-stocking points

D 3.3.2 – Population genetic database ofRussian sturgeon broodstock

D 3.4.1 – Design for the implementation oftwo pilot ex-situ gene conservation sites in-cluding complete technical facility- andaquaculture system design with cost estima-tion

D 3.4.2 – Preparation of project proposaland recommended funding sources for theimplementation of two pilot ex-situ sites,based on the obtained system design

D 3.4.3 – Report on the visits to threeEuropean sturgeon farms

D 4.1.1 – Analysis of Management andPolicy Plans

9.4 Literature and documents

Apostolos, A., Cvĳanović, G., Iani, M.,Kubala, M., Lenhardt, M., Mihov, S.,Nastase, A., Paraschiv, M., Pehlivanov, L. &Pekarik, L. Smederevac-Lalic, M., Suciu, R.,2020: Migratory Fish in the Danube Region.MEASURES support document, MS-Word79 pp. as of 17.09.2020.

Bammer, V., Apostolou, A., Bulat, D., Du-mitrascu, O.C., Effenberger, M., Erös, T.,Hortic, S., Kováč, V., Simonovič, P. 2021:Fish. In: Liška, I., Wagner, F., Sengl, M.,Deutsch, K., Slobodník, J., Paunović, M.Joint Danube Survey 4. ICPDR, Vienna, pp41-54.

BDS, Biodiversity Strategy, Communicationfrom the Commission to the European Par-liament, the Council, the European Eco-nomic and Social Committee and The Com-mittee of the Regions EU related to theforthcoming Biodiversity Strategy for 2030 -Bringing nature back into our lives (COM/2020/380).

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Berra, T.M., 2007: Freshwater Fish Distribu-tion, The University of Chicago Press, Ltd.,London, 606 pp.

Cokan, B., Paraschiv, M., Pekarik, L., 2021:Danube Migratory Fish Habitat Manual.Danube Delta Technological PublishingHouse, Tulcea, Romania.

DANUBEPARKS, 2019: Ecological Con-nectivity in the Danube River Basin. FuturePerspectives and Guiding Principles. Orthan der Donau, 64 pp.

Daufresne, M. & Boët, P., 2007: Climatechange impacts on structure and diversityof fish communities in rivers. GlobalChange Biology (2007) 13, pp 2467-2478.

Deinet, S., Scott-Gatty, K., Rotton, H.,Twardek, W.M., Marconi, V., McRae, L.,Baumgartner, L.J., Brink, K., Claussen, J.E.,Cooke, S.J., Darwall, W., Eriksson, B.K., Gar-cia, de Leaniz, C., Hogan, Z., Royte, J., Silva,L.G.M., Thieme, M.L., Tickner, D., Wald-man, J., Wanningen, H., Weyl, O.L.F. &Berkhuysen, A., 2020: The Living Planet In-dex (LPI) for migratory freshwater fish –Technical Report. World Fish MigrationFoundation, The Netherlands. 55 pp.

DSTF, 2020: Position Paper on the sturgeonfishing moratorium in the Danube Riverand Black Sea - extended version. 35 pp. ht-tps://dstf.info/wp-content/uploads/2020/09/DSTF-Fishing-Moratorium-Paper.pdf

DSTF, Peteri, A., Reinartz, R., Friedrich, T. &Sandu, C., 2016: Ex-situ survey to preservesturgeon genetic diversity in the Middleand Lower Danube (Acronym:STURGENE). EU Strategy for the DanubeRegion, START Program – call 1, Final Re-port, 26 p.

EFI+-Consortium 2008: http://efi-plus.bok-u.ac.at/

EU-SDR, 2020: ACTION PLAN - EuropeanUnion Strategy for Danube Region. Brus-sels, 6.4.2020, SWD(2020) 59 final, 82 pp.

FAO, 2019: Regional Conference on riverhabitat restoration for inland fisheries in theDanube river Basin and adjacent Black SeaAreas. Conference Proceedings, 13–15November 2018, Bucharest, Romania. FAOFisheries and Aquaculture Proceedings No.63. Rome. https://doi.org/10.4060/ca5741en. 74 pp.

FAO/DVWK, 2002: Fish passes – Design,dimensions and monitoring. Rome, FAO.2002. 119 pp. http://www.fao.org/3/y4454e/y4454e00.htm

FD, Flood Directive: Directive 2007/60/ECof the European Parliament and of theCouncil of 23 October 2007 on the assess-ment and management of flood risks.

Freshwater andMarine Image Bank, Univer-sity of Washington: https://content.lib.wash-ington.edu/fishweb/index.html

Friedrich, T., Reinartz, R. & Gessner, J., 2019:Sturgeon re-introduction in the Upper andMiddle Danube River Basin. J Appl Ich-thyol. 2019;35:1059-1068.

Geist, J. & Hawkins, S.J., 2016: Habitat re-covery and restoration in aquatic ecosys-tems: current progress and future chal-lenges, Aquatic Conserv: Mar. Freshw. Eco-syst. 26 (2016): 942–962.

Groves, C.R., Jensen, D.B., Valutis, L.L.,Redford, K.H., Shaffer, M.L., Scott, J.M.,Baumgartner, J.V., Higgins, J.V., Beck, M.W.& Anderson, M.G., 2002: Planning for Biod-iversity Conservation: Putting ConservationScience into Practice: A seven-step frame-

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work for developing regional plans to con-serve biological diversity, based upon prin-ciples of conservation biology and ecology,is being used extensively by the nature con-servancy to identify priority areas for con-servation. BioScience, Vol. 52, Issue 6, June2002, 499-512.

HD, Habitat Directive: Council Directive92/43/EEC of 21 May 1992 on the conserva-tion of natural habitats and of wild faunaand flora.

Hohensinner, S., 2020: Wien und die Donau.Mitteilungen der Deutschen Gesellschaftfür Archäologie des Mittelalters und derNeuzeit, 33, 255-265.

ICPDR: The Danube River basin – Facts andFigures http://www.icpdr.org/flowpaper/app/services/view.php?doc=icpdr_facts-_figures.pdf&format=pdf&page={page}&subfolder=default/files/nodes/docu-ments/ Last accessed April 3rd, 2020

ICPDR, 2015: Danube River Basin DistrictManagement Plan (DRBMP) - Update 2015,192p. . http://www.icpdr.org/main/man-agement-plans-danube-river-basin-pub-lished

ICPDR, 2018: ICPDR Sturgeon Strategy. Ver-sion: FINAL, Date: 29-01-2018, 20 pp., ht-tps://www.icpdr.org/main/sites/default/files/nodes/documents/om-20_-_3.4_icp-dr_sturgeon_strategy_endorsed_version_fi-nal.pdf

Jungwirth, M., Haidvogl, G., Moog, O.,Muhar, S. & Schmutz, S., 2003: AngewandteFischö̈kologie an Fliessgewä̈ssern. FacultasUniversitä̈tsverlag, Vienna, Austria. 547 pp.

Jungwirth, M., Haidvogl, G., Hohensinner,S., Waidbacher, H. & Zauner, G., 2014: Öster-reichs Donau. Landschaft-Fisch-Geschichte.Institut für Hydrobiologie und Gewässer-

management, BOKUWien, 420 pp.

Keckeis, H. & Schiemer, F., 2002: Under-standing conservation issues of the DanubeRiver. Fishery Science: The Unique Contri-bution of Early Life Stages. Blackwell Pub-lishing, Oxford pp. 272-288 (2002).

Kottelat, M. & Freyhof, J., 2007: Handbookof European Freshwater Fishes. Publica-tions Kottelat, 646 pp.

Kottelat, M. & Freyhof, J., 2009: Notes onthe taxonomy and nomenclature of someEuropean freshwater fishes. IchthyologicalExploration of Freshwaters 20 (1): 75-90.

Kováč, V., 2015: Current Status of Fish Com-munities in the Danube. The Danube RiverBasin, 359-388. doi:10.1007/698_2015_377.

Lenhardt, M., 2021: pers. comm. on the oc-currence of shad species upstream the IronGate dams (unpublished data).

Ludwig, A., 2020: pers. comm. on the statusof Acipenser nudiventris in the Danube ac-cording to the latest IUCN assessment.

Maxted, N., 2013: In Situ, Ex Situ Conserva-tion. Encyclopedia of Biodiversity, Vol. 4, pp313–323.

MSFD, Marine Strategy Framework Direct-ive: Directive 2008/56/EC of the EuropeanParliament and of the Council of 17 June2008 establishing a framework for com-munity action in the field of marine envir-onmental policy.

PAN-EUAP (PAN-European Action Planfor Sturgeons). Friedrich, T., Gessner, J., Re-inartz, R. & Striebel-Greiter, B. (eds.), 2018:Convention on the Conservation ofEuropean Wildlife and Natural Habitats,Council of Europe Publishing, 85 p.https://rm.coe.int/pan-european-action-

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Pletterbauer, F., Melcher, A. H., Ferreira, T.& Schmutz, S., 2014: Impact of climatechange on the structure of fish assemblagesin European rivers. Hydrobiologia, DOI10.1007/s10750-014-2079-y.

Povž, M., 2016: Ribe in Piškurji v porečjuMure v Slovenĳi (Fishes and Lampreys inthe Mura River Basin in Slovenia). Proteus,Ljubljana 78(6,7,8), 339-345.

Reinartz, R., 2015: Feasibility Study: Ex-situmeasures for Danube River Sturgeons(Acipenseridae). Part of the project "Elabor-ation of pre-requisites for sturgeon conser-vation in the Danube River Basin" on behalfof University of Natural Resources and LifeSciences, Vienna (BOKU)/ Institute of Hy-drobiology and Aquatic Ecosystem Man-agement and the International Commissionfor the Protection of the Danube River(ICPDR). 72 pp. unpublished.

Schiemer, F., Guti, G., Keckeis, H. & StarasM., 2003: Ecological Status and Problems ofthe Danube River and its Fish Fauna: a re-view, Proceedings of the Second Interna-tional Symposium on the Management oflarge rivers for Fisheries, Sustaining Liveli-hoods and Biodiversity in the New Mil-lenium 11th - 14th February 2003 in PhnomPenh, Kingdom of Cambodia, Welcomme,R.L. & Petr, T. (eds.), Volume I, pp. 273-299.

Schmutz S., Mielach C., 2013: Measures forensuring fish migration at transversal struc-tures. ICPDR, Vienna, 52 pp.

Simonović P., Povž M., Piria M., Treer T.,Adrović A., Škrĳelj R.; Nikolić V., Simić V.,2015: Ichthyofauna of the River Sava Sys-tem. In: Milačič R., Ščančar J., Paunović M.(eds) The Sava River. The Handbook of En-vironmental Chemistry, vol 31. Springer,Berlin, Heidelberg. pp. 361-400. https://

doi.org/10.1007/978-3-662-44034-6_14.

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Stagl, J. C. & Hattermann, F. F. (2015): Im-pacts of Climate Change on the Hydrolo-gical Regime of the Danube River and ItsTributaries Using an Ensemble of ClimateScenarios. Water 2015, 7, 6139-6172.

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Strategy for ecological corridor conservation and restoration in ...

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