Trophic flows, ecosystem structure and fishing impacts in the South Catalan Sea, Northwestern Mediterranean

www.elsevier.com/locate/jmarsys

Journal of Marine System

Trophic flows, ecosystem structure and fishing impacts in the

South Catalan Sea, Northwestern Mediterranean

Marta Coll a,*, Isabel Palomera a, Sergi Tudela b, Francesc Sarda a

a Institute of Marine Science (CMIMA-CSIC), Passeig Marıtim de la Barceloneta, 37- 49, 08003, Barcelona, Spainb WWF Mediterranean Programme Office, Canuda, 37, 08002, Barcelona, Spain

Received 21 February 2005; accepted 15 September 2005

Abstract

An exploited ecosystem from the continental shelf and upper slope of the Northwestern Mediterranean Sea was described by

means of an Ecopath mass-balance model with the aim of characterising its functioning and structure and describing the ecosystem

impacts of fishing. This application included some complexities added to the general modelling methodology due to the high

biodiversity of the Mediterranean Sea and the multispecific nature of the fishery, and to the difficulties of working with fishing data

which are usually irregularly or imprecisely collected. The model comprised 40 functional groups including primary producers, the

main species of benthic, demersal and pelagic invertebrates, fishes and non-fish vertebrates and three detritus groups. In addition,

trawling, purse seine, longline and troll bait fishing fleets were included.

Results showed that the functional groups were organized into four trophic levels with the highest levels corresponding to

anglerfish, dolphins, large pelagic fishes and adult hake. The system was dominated by the pelagic fraction, where sardine and

anchovy prevailed in terms of fish biomasses and catches. Detritus and detritivorous groups also played key roles in the ecosystem

and important coupled pelagic-demersal interactions were described. Considering Odum’s theory of ecosystem development, the

ecosystem was placed on an intermediate-low developmental stage due, at least partially, to the impact of fishing activity. This

highlighted the high intensity of fishing in the ecosystem, in accordance with the general assessment of western Mediterranean

marine resources, and fishing fleets were ranked as top predators of the system. The low trophic level of the catch was in line with the

long history of exploitation in the area. However, the steady decline of pelagic landings between 1994 and 2003, coupled with a

decrease of the pelagic biomass within the system, underlined the low resistance of the system in front of perturbations. This decline

was reproduced under Ecosim dynamic simulations combining different scenarios of moderate increase of fishing effort and an

environmental forcing affecting the availability of preys to small and medium-sized pelagic fishes under wasp-waist flow control.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Ecopath; Ecosim; Ecological modelling; Trophic web; Network analysis; Fishing impact; Environmental forcing; Mediterranean; Ebro

Delta

0924-7963/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.jmarsys.2005.09.001

* Corresponding author.

E-mail addresses: [email protected] (M. Coll),

[email protected] (I. Palomera), [email protected] (S. Tudela),

[email protected] (F. Sarda).

1. Introduction

The Mediterranean region has been inhabited for

millennia and human settlements have been spreading

continuously along its coastal areas, reaching a total of

132–135 million people now settled there (Margalef,

1985). Ecosystems have thus been altered in many ways

s 59 (2006) 63–96

M. Coll et al. / Journal of Marine Systems 59 (2006) 63–9664

due to the overexploitation of biological resources,

direct habitat modification of sea and coastal areas,

introduction of exotic species, pollution and climate

change; with many species presently endangered and

some probably prone to extinction (Bianchi and Morri,

2000). Fishing activity has been proposed as the first

major human disturbance to coastal areas (Jackson et

al., 2001), and evidence of fishing activity going back to

ancient times can be found all around the Mediterranean

Sea (Margalef, 1985). This is emphasised by a much

lower starting value of the mean trophic level of the

catch in the past 50-year historical series for the Med-

iterranean Sea when compared to oceanic areas of the

world (Pauly et al., 1998a).

Two important features of the fishing activity in the

Mediterranean Sea are the multi-specificity of catches

and the absence of large single stocks, especially in the

demersal regime, comparable to those which inhabit

other seas (Farrugio et al., 1993). Moreover, although

artisanal gears are still important within the western

basin, most fleets have developed towards a nearly

industrial type of activity (or semi-industrial fleets)

fully exploiting continental shelves and upper slopes

of the basin. They are associated with the highest land-

ings and are mainly composed of bottom trawlers, purse

seines and longliners (Lleonart and Maynou, 2003). The

development of fishing technologies and overcapitaliza-

tion, with an increasing demand for marine resources, is

placing intensive pressure on marine resources in the

western basin, and the general assessment suggests that

most demersal stocks are fully exploited or over-

exploited, while some pelagic stocks also show overex-

ploitation trends (Farrugio et al., 1993; Aldebert and

Recasens, 1996; Sarda, 1998; Papaconstantinou and

Farrugio, 2000; Lleonart and Maynou, 2003; Bas et

al., 2003). Increasing concern about recruitment over-

fishing is related to the Northwestern Mediterranean

anchovy stocks, while growth overfishing affects some

demersal resources because for many species the sizes at

first catch are very similar to those at which the fish

recruit (Lloret and Lleonart, 2002; Sarda et al., 2005).

Moreover, the introduction of new fishing procedures

such as modern longlines, e.g., for adult hake Merluc-

cius merluccius, has eliminated the spawning refugia of

some species and has lead to an increasing concern for

recruitment overfishing of some demersal stocks (Lleo-

nart and Maynou, 2003).

Fishing activities are developed within a context, the

ecosystem, where target and non-target species interact

establishing complex relationships. Fishing will thus

have various direct and indirect impacts, additionally

to those induced by oceanographic features and other

anthropogenic and natural disturbances (e.g., Jennings

and Kaiser, 1998; Hall, 1999; Jackson et al., 2001;

Christensen et al., 2003; Myers and Worm, 2003). In

this context, there is a growing need to apply more

integrative approaches to fisheries management to un-

derstand how fishing activity is impacting complex food

web structures and functioning (FAO, 2002; Pauly et al.,

2002).

Therefore, an ecological model using the Ecopath

with Ecosim software (EwE) (Christensen and Walters,

2004; Pauly et al., 2000) was applied to describe a well

known area from the Northwestern Mediterranean Sea:

the exploited continental shelf and upper slope ecosys-

tem of the South Catalan Sea associated with the Ebro

River Delta. The mass-balance modelling approach has

been widely used to quantitatively describe aquatic

systems and to assess the impacts that fishing activities

and environmental factors have on marine ecosystems

(Christensen and Pauly, 1993a; Christensen and Wal-

ters, 2004). However, there are still few examples of

ecological modelling applied to the exploited ecosys-

tems of the Mediterranean Sea and most are concen-

trated in coastal and shallow areas (Orek, 2000;

Daskalov, 2002; Libralato et al., 2002; Pinnegar and

Polunin, 2004). The present application is the first

effort to study western Mediterranean exploited shelf

and slope ecosystems using a mass balance model. It

has enabled the description of the structure and func-

tioning of this ecosystem with the analysis of a broad

number of ecological indicators related with trophic

flow description, thermodynamic concepts, information

theory and network analysis (Muller, 1997; Christensen

et al., 2004). Moreover, fishing activities are considered

within the ecosystem context to assess the ecosystem

effects of fishing.

According to FAO (1995) dThe achievement of real

marine ecosystem-based management of fisheries

implies the regulation of the use of the living resources

based on the understanding of the structure and dynam-

ics of the ecosystem of which the resource is a part’. This

clearly demands a substantial improvement of our un-

derstanding of the structure and functioning of eco-

systems, and the interactions between ecosystem

compartments and their changes due to human and en-

vironmental factors.

2. Materials and methods

2.1. The study area

An Ecopath with Ecosim (EwE) trophic model

(Christensen and Walters, 2004; Pauly et al., 2000)

Fig. 1. The continental shelf and upper slope area of the South Catalan Sea related with the Ebro River Delta (Northwestern Mediterranean).

M. Coll et al. / Journal of Marine Systems 59 (2005) 63–96 65

was described to represent an average annual situation

(1994) of the continental shelf and upper slope area

associated with the Ebro River Delta (South Catalan

Sea, Northwestern Mediterranean) (Coll et al., 2004)

(Fig. 1). The considered depth range was between 50

and 400 m, covering a total area of soft bottom

sediments of 4500 km2. The coastal area within 3

nm from the coast or down to 50 m depth, where

the artisanal fleet mainly operates and the trawling

fleet is not allowed to fish, was excluded.

This is an oligotrophic area, where enrichment

occurs due to regional environmental events, mainly

related to wind conditions, the existence of a temporal

thermocline and a shelf-slope current and river dis-

charges (Estrada, 1996; Salat, 1996; Agostini and

Bakun, 2002). These episodes greatly influence the

productivity and fishing activity of the area (Palo-

mera, 1992; Sabates and Olivar, 1996; Agostini and

Bakun, 2002; Lloret et al., 2004), which yields almost

half of the total landings of the Catalan coast (Lleo-

nart, 1990) and which is specially relevant for the

reproduction of small pelagic fishes, mainly the Euro-

pean anchovy Engraulis encrasicolus. Moreover, this

is also a strategic area for marine vertebrate conser-

vation, sheltering three quarters of the world’s

breeding population of the Mediterranean endemic

Audouin’s Gull (Larus audouinii) and important col-

onies of other terns and gulls (Zotier et al., 1998;

Abello et al., 2003). Some of these species forage

actively on the marine shelf and find a complementary

food source in the discards generated by the trawling

and purse seine fleets (Oro et al., 1997; Oro and Ruız,

1997; Arcos, 2001).

The area includes the fishing harbours from Tarra-

gona to Les Cases d’Alcanar (Fig. 1). Trawling (with

174 boats operating in the study area), purse seine (51

boats), longline (13 boats) and troll bait fleet (few

seasonal boats) were included in the model. Small

pelagic fishes, overcoat sardine (Sardina pilchardus)

and anchovy (Engraulis encrasicolus), constitute the

principal component of the catches in terms of biomass

and are mainly caught by purse seines and bottom

trawlers. The demersal fishery comprises mainly juve-

niles of several target species, e.g. hake (Merluccius

merluccius), red mullet (Mullus barbatus) and blue

whiting (Micromesistius poutassou), caught principally

by the trawling fleet. Large demersal fish (e.g., adult

hake) and large pelagic fish (e.g., Atlantic bonito Sarda

sarda, bluefin tuna Thunnus thynnus and swordfish

Xiphias gladius) are caught by longline and troll bait

fleets (Bas et al., 1985; Lleonart, 1990; Lloret and

Lleonart, 2002).

ig. 3. Total official landings (t), demersal landings and small and

edium-sized pelagic fish landings from the studied area (Institute of

arine Science, CMIMA-CSIC, and Generalitat de Catalunya data-

ases) (1994–2003).


Themodel represented the highly fished ecosystem in

1994, when official landings were at their highest his-

torical level. Official landings from the studied area

increased dramatically from the early 1960s to the

early 1980s, mainly due to governmental aids to the

fishing sector. Marked fluctuations in landings occurred

thereafter until catches progressively declined from 1994

to the present (Fig. 2). Total official landings from 2003

were similar to those reached in the late 1970s. From

1994 to 2003 a decrease of 55% on total official landings

has been observed (Fig. 3). This reduction is mainly

based on the pelagic fraction, which also exhibited

marked interannual fluctuations and underwent a reduc-

tion of 70.2% in the case of anchovy official landings and

a reduction of 70% in the case of sardine landings.

Demersal landings have been maintained at similar

levels since 1983 with a reduction of 18% in landings

and underwent smaller fluctuations over the period of

decline in the pelagic fraction. Pelagic and demersal

landings reached similar values for the first time in 2003.

2.2. Modelling approach

The Ecopath and Ecosim approach (EwE) version 5

(Christensen and Walters, 2004; Pauly et al., 2000;

http://www.ecopath.org) was used to ensure energy

balance of the model. EwE divides the production

(P) of each component, or functional group, (i), of

the ecosystem into predation mortality (M2ij) caused

by the biomass of the other predators (Bj); exports from

the system both from fishing activity (Yi) and other

exports (Ei); biomass accumulation in the ecosystem

(BAi); and baseline mortality or other mortality (1-EEi),

where EE is the ecotrophic efficiency of the group

within the system, or the proportion of the production

Fig. 2. Total official landings and pelagic and demersal fractions (t)

from the studied area (Institute of Marine Science, CMIMA-CSIC,

and Generalitat de Catalunya databases) (1973–2003).

F

m

M

b

of (i) that is exported out of the ecosystem (i.e., by

fishing activity) or consumed by predators within it.

Pi ¼Xj

BjdM2ij þ Yi þ Ei þ BAi þ Pid 1� EEið Þ:

ð1ÞEq. (1) can be re-expressed as:

BdP

B

��i

¼Xj

BjdQ

B

��j

dDCij þ Yi þ Ei þ BAj

þ BidP

B

��i

d 1� EEið Þ: ð2Þ

Where (P/B)i indicates the production of (i) per unit

of biomass and is equivalent to total mortality, or Z,

under steady-state conditions (Allen, 1971); (Q/B)i is

the consumption of (i) per unit of biomass; and DCij

indicates the proportion of (i) that is in the diet of

predator ( j) in terms of volume or weight units. EwE

parameterizes the model by describing a system of

linear equations for all the functional groups of the

model, where for each equation three of the basic

parameters: Bi, (P/B)i, (Q/B)i or EEi have to be

know for each group (i). The unassimilation rate (or

the fraction of the food consumption that is not assim-

ilated, U/Q) and the fate of detritus are also required.

The energy balance within each group is ensured when

consumption by group (i) equals production by (i),

respiration by (i) and food that is unassimilated by (i).

To ensure consistence between ontogenetic groups, the

multiple stanza representation (Christensen and Walters,

2004) was used for modelling European hake, a highly

commercial species for which dietary information is

available for the different population fractions (Bozzano

et al., 1997, in press). Two groups were defined, namely

http:\\www.ecopath.org


juvenile hake (b2years old or 25 cm) and adult hake

(z2 years old or 25 cm) (Recasens, 1992; Recasens and

Lleonart, 1999). (P/B)i and diet composition were pro-

vided for both groups, while Bi and (Q/B)i were intro-

duced for the leading stanza group only, juvenile hake.

The Automatic Mass Balance Procedure (Kavanagh

et al., 2004) was used after having modified some

errors on diet composition (mainly on cephalopods

and medium-sized pelagic fish where available trophic

information was not from the studied area) and bio-

mass for those groups whose initial biomasses were

assessed by the swept area method (maximum bio-

masses were used in these cases). The automatic

procedure modified the diet matrix, and to a lesser

extent biomass data, as they were considered the

parameters with a higher associated uncertainty. The

model was considered balanced when: 1) realistic

estimates of the missing parameters of EE were cal-

culated (EEb1); 2) values of P/Q for functional

groups (GEi or the gross food conversion efficiency)

were between 0.1 and 0.35 with the exception of fast

growing groups with higher GEi and top predators

with lower values; and 3) values of R/B were consis-

tent with the group’s activities with high values for

small organisms and top predators (Christensen et al.,

2004). The Pedigree routine was used to describe the

origin and quality of the model, while a sensitivity

analysis routine was used to explore the uncertainty of

the parameter estimates and the impact of such uncer-

tainty on the mass balance model (Christensen and

Walters, 2004; Christensen et al., 2004).

Finally, various hypotheses were preliminarily tested

in relation to the decreasing trend of official pelagic

landings reported from 1994 to the present. To do this,

the Ecosim temporal dynamic module of the software

(Walters et al., 1997) was used. The Ecosim module

takes the previous equations and sets up a series of

differential equations:

dBi

dt¼ P

Q

��i

dX

Qji �X

Qijþ Ii

� Mi þ Fi þ eið ÞdBi ð3Þ

Where dBi/dt is the growth rate during the time

interval dt of (i) in terms of Bi; (P/Q)i is the gross

efficiency; Mi is the non-predation natural mortality

rate; Fi is the fishing mortality rate; ei is the emigration

rate; Ii is the immigration rate; and ei Bi� Ii is the net

migration rate. Calculations of consumption rates (Q)

are based upon the bforaging arenaQ theory where the

biomass of (i) is divided between a vulnerable and an

non-vulnerable fraction and the transfer rate (t) be-

tween the two fractions is what determines the flow

control (Walters et al., 1997; Christensen and Walters,

2004).

2.3. Model parameters and functional groups

The model represents an annual average situation of

the South Catalan Sea ecosystem in 1994. Pelagic bio-

masses and catches were thus related to this one year,

but, due to poor data availability for 1994, demersal

biomass data were used for an extended period from

1994 to 2000, so to cover a full year’s seasonality.

Biomass values were obtained from the swept area

method, the egg production method, acoustic surveys

and information available in the literature. Production/

biomass ratios (P/B) and consumption/biomass ratios

(Q/B) were taken from the literature or obtained from the

application of empirical equations using length and

weight data (Nilsson and Nilsson, 1976; Pauly, 1980;

Innes et al., 1987; Pauly et al., 1990; Christensen et al.,

2004), whilst diet composition and assimilation rates

where compiled from published information. In the ab-

sence of information, steady state conditions were as-

sumed with BAi =0 and Ei =0.

Migratory patterns of Atlantic bonito, large pelagic

fishes, fin whale and marine turtles were taken into

account within the model by modelling a proportion of

the diet composition of these groups as imports to the

system (De La Serna and A lot, 1990; Grannier, 1998;

Block et al., 2001; Sabates and Recasens, 2001; Tomas

et al., 2001; Christensen and Walters, 2004). The

microbial food web was not directly considered in

the model, but it was indirectly considered within the

zooplankton diet composition and detritus dynamics

(Calbet et al., 2002).

Official landings statistics from 1994 concerning

trawling, purse seine, longline and troll bait fleets were

corrected by considering discard information drawn

from the literature (including by-catch of vulnerable

species of cetaceans, seabirds and turtles) (e.g., Arcos,

2001; Belda and Sanchez, 2001; Caminas, 1988; Cami-

nas and De la Serna, 1995; Sanchez et al., 2004; Tudela,

2004) and new estimates of illegal, unregulated or unre-

ported (IUU) landings. In order to assess the extent of

IUU landings in the Catalan Sea, short surveys were

conducted in the main fishing ports during 2002 and

straightforward questionnaires were delivered to the

fishermen’s representatives. Average IUU estimates

amounted to 25% of the official landings on an annual

basis, while in some cases and for some species IUU

comprised 50% to 90% of the official data (Fig. 4).

Consumption of discards by scavenger species was con-

Fig. 4. Estimates of illegal unreported or unregulated (IUU) landings for target fishes and invertebrate species of the continental shelf and upper

slope (Catalan Sea) as a percentage of reported official landings.


sidered within the model by taking into account the main

results of research in the area (Bosch et al., 1994; Oro,

1996; Oro and Ruız, 1997; Oro et al., 1997; Granadeiro

et al., 1998; Arcos, 2001; Tomas et al., 2001; Bozzano

and Sarda, 2002).

Input data is listed in Table 1; main data sources and

estimation methods are compiled in Table A1. The

model included 40 functional groups spanning the

main trophic components of the ecosystem and including

target and non-target fish and invertebrate groups (Tables

1 and A1), and three detritus groups (natural detritus,

discards and by-catch of vulnerable species of cetaceans,

seabirds andmarine turtles). Definition of the groups was

based on similarities in their ecological and biological

features (e.g., feeding, habitat, mortality) and on the

importance of the species in terms of the fisheries. In

addition, dealing with the high biodiversity of the Med-

iterranean Sea implied a systematic analysis of available

ecological information. Factorial Correspondence Anal-

ysis (FCA) and Hierarchical Custer Analysis were ap-

plied to published stomach-content data for 44 fish

species to establish new mixed groups of benthic, de-

mersal and benthopelagic species. When defined, these

new groups where added to the rest of groups and input

data was integrated taking into account species compo-

sition and biomasses proportions within each group.

2.4. Model analysis

After balancing the model, ecological analyses

integrated in EwE were used to examine various

indicators based on trophic flow description, thermo-

dynamic concepts, information theory and network

analysis (Muller, 1997; Christensen et al., 2004).

Some of these results are related with the ecosystem

development theory sensu Odum (1969, 1971) (Lin-

deman, 1942; Odum and Heald, 1975; Finn, 1976;

Ulanowicz, 1986, Christensen and Pauly, 1993b;

Christensen, 1995a; Ulanowicz, 1995). The mixed

trophic impact routine, derived from economic theory

(Leontief, 1951; Ulanowicz and Puccia, 1990), allowed

the quantification of direct and indirect trophic interac-

tions among groups. In this analysis, the positive or

negative impact that a hypothetical increase in the

biomass of a group would produce on the other groups

of the ecosystem is provided, including the fisheries.

The primary production required to sustain the fishery,

the trophic level of total catch, the omnivory indices,

mortalities and the relative consumption of total pro-

duction, excluding plankton and benthic invertebrates,

and of fish production were analysed to place the

fisheries into their ecosystem context (Pauly and Chris-

tensen, 1995; Pauly et al., 1998a; Christensen and

Walters, 2004).

Dynamic simulations with Ecosim were carried out

using the 1994 model to test hypotheses to reproduce

the most recent intense decrease of pelagic landings in

the area from 1994–2003 (Fig. 2) and the low bio-

masses for sardine and anchovy; anchovy being more

abundant than sardine in recent years considering

results from stock assessments (Quintanilla et al.,

2004; Torres et al., 2004). Until the beginning of

Table 1

Input data of the South Catalan Sea model by functional group

Functional group Bi P/B Q/B U/Q Landings Discards

1 Phytoplankton 10.20 37.91 – – – –

2 Micro and mesozooplankton 7.79 20.87 48.85 0.40 – –

3 Macrozooplankton 0.54 20.41 50.94 0.20 – –

4 Jellyfish 0.39 28.51 50.48 0.20 – –

5 Suprabenthos 0.03 8.05 52.12 0.30 – –

6 Polychaetes 15.54 1.82 11.53 0.60 – –

7 Shrimps 0.03 3.08 7.20 0.20 0.035 0.012

8 Crabs 0.09 2.10 4.73 0.20 0.113 0.034

9 Norway lobster 0.03 1.20 4.56 0.20 0.013 0.001

10 Benthic invertebrates 8.87 1.02 3.13 0.43 0.009 0.003

11 Benthic cephalopods 0.13 2.34 5.30 0.13 0.221 0.011

12 Benthopelagic cephalopods 0.14 2.02 26.47 0.40 0.038 0.002

13 Mullets 0.06 2.29 6.90 0.20 0.106 0.005

14 Conger eel 0.03 1.56 2.88 0.20 0.042 0.002

15 Anglerfish 0.05 1.58 2.70 0.20 0.069 0.003

16 Flatfishes 0.04 2.10 7.53 0.20 0.061 0.003

17 Poor cod 0.02 1.52 6.97 0.20 0.014 0.004

18 Juvenile hake 0.02 1.30 7.37 0.20 0.020 0.001

19 Adult hake – 0.60 – 0.20 0.198 0.010

20 Blue whiting 0.66 0.66 5.93 0.20 0.132 0.040

21 Demersal fishes (1) 0.32 1.16 6.85 0.20 0.130 0.039

22 Demersal fishes (2) 0.01 1.00 7.17 0.20 0.005 0.002

23 Demersal fishes (3) 0.09 0.43 6.25 0.20 0.001 0.000

24 Demersal small sharks 0.06 0.42 5.43 0.20 0.005 0.001

25 Bentopelagic fishes 0.12 1.37 9.03 0.30 0.050 0.015

26 European anchovy 2.44 1.33 13.91 0.30 0.897 0.045

27 European pilchard 3.37 1.50 8.86 0.30 2.693 0.135

28 Small pelagic fishes 0.69 0.52 7.39 0.30 0.012 0.004

29 Horse mackerel 1.75 0.39 5.13 0.20 0.021 0.001

30 Mackerel 0.68 0.46 4.88 0.20 0.058 0.003

31 Atlantic bonito 0.30 0.35 4.36 0.20 0.011 0.0006

32 Large pelagic fishes 0.14 0.43 1.63 0.20 0.046 0.0018

33 Loggerhead turtle 0.03 0.15 2.54 0.20 – 0.0003

34 Audouins gull 0.001 4.64 70.00 0.20 – 0.00002

35 Other sea birds 0.001 4.56 73.20 0.20 – 0.00002

36 Dolphins 0.03 0.07 13.49 0.20 – 0.0014

37 Fin whale 0.40 0.04 4.11 0.30 – –

38 Detritus 70.00 – – – – –

39 Discards 0.38 – – – – –

40 By-catch 0.002 – – – – –

Table A1 lists main data sources and estimation methods.

Bi=Initial biomass (t km�2 ); P/B=Production/biomass ratio (years�1); Q/B=Consumption/biomass ratio (years�1 ); U/Q=Unassimilated food;

Landings and discards (t km �2 years�1 ).


2000s, sardine has been more abundant than anchovy

in previous assessments from the 1980s. A total of 135

different theoretical scenarios were applied to fishing

effort, environmental forcing and flow control situa-

tions based on previous work from the Southern Ben-

guela of dynamics of small and medium-sized pelagic

fishes and their preys related to overfishing situations

and large scale environmental changes (Shannon et al.,

2004). The scenarios defined were: a) four fishing

effort scenarios: no increase of fishing effort and

increases of 10%, 20% and 30% from 1994 to 2004

for trawling and purse seine fleets; b) Nine environ-

mental forcing functions: no forcing function and for-

cing function of 10%, 20% and 30% affecting the

interaction between small and medium-sized pelagic

fishes and their preys in 10, 5 and 1 years of the

simulation; c) three flow control situations: mixed

control, bottom-up and wasp-waist control to describe

interactions between functional groups (Cury et al.,

2000; Shannon et al., 2000).

Default values of vulnerabilities v =2 were used to

represent mixed flow control, whilst values of v =1

were set to describe vulnerability of phytoplankton and

zooplankton groups to their predators to represent bot-

Fig. 5. Results from the Factorial Correspondence Analysis of trophic data of 44 fish species with first and second axes represented (species codes

are listed in Table A2).


tom-up flow control. Values of vN1 of the prey to small

and medium-sized pelagic fish (top-down control of

small and medium-sized pelagic fish on their prey) and

v =1 of small and medium-sized pelagic fish to their

predators (bottom-up control of small and medium-

sized pelagic fish on their predators) were set to represent

wasp-waist flow control in the ecosystem. The generic

Fig. 6. Results from the Factorial Correspondence Analysis of trophic data of

listed in Table A2).

environmental forcing function applied to affect the

interaction of small and medium-sized pelagic fishes

and their preys, phytoplankton and zooplankton, had

the aim to reproduce a generic environmental anomaly

that would have negatively affected the availability of

prey by these fish groups. This function could be related

to direct or indirect anthropogenic or climatic factors,

44 fish species with first and third axes represented (species codes are

Fig. 7. Cluster analysis representing similitude between 44 fish spe

cies analyzed with the Factorial Correspondence Analysis (species

codes are listed in Table A2).


e.g., a decrease of the Ebro river runoff through time

(Lloret et al., 2004), an increase of water surface tem-

perature (Salat and Pascual, 2002) or an increase of

gelatinous plankton (Buecher, 1999).

3. Results and discussion

3.1. Factorial Correspondence Analysis

Three factors accumulated 45.56%of the total variance

in the Factorial Correspondence Analysis (FCA) of the 44

fish species that needed to be grouped. Factors 1 and 2

(representing the first and second axes) explained 18.45%

and 15.24%of variance, respectively (Fig. 5), and factor 3

explained 11.86% of variance (Fig. 6) (Species codes for

Figs. 5, 6 and 7 are listed in Table A2). Zooplankton had

positive values along the first axis, while cephalopods,

fish species, benthic invertebrate, detritus and jellyfish

had negative values. Along the second axis, benthic

invertebrates had a highly positive value, followed by

jellyfish, detritus, polychaetes and zooplankton, while

cephalopods, fish species, suprabenthos and decapod

crustaceans showed negative values. Finally, a total of

4 new groups were defined from the FCA and are

illustrated in the cluster analysis (Fig. 7):

– Class 1 was composed of demersal fish species with

mixed trophic habits (main prey being benthic inver-

tebrates, detritus, suprabenthos, crustaceans, cephalo-

pods and small demersal fishes) and was named

bdemersal fishes (1)Q;– Class 2 was composed of demersal fishes with trophic

habits based on non-crustacean benthic invertebrates

mainly (main prey being brittlestars, starfish, gastro-

pods, etc.) and was named bdemersal fishes (2)Q;– Class 3 was composed of demersal fishes with trophic

habits based on small demersal and pelagic fishes as

main prey species andwas named bdemersal fishes (3)Q;– Class 4 and Class 5 were composed of benthopelagic

fish species with trophic habits based on zooplankton.

These latter two classes were joined together in a single

functional group named bbenthopelagic fishesQ.

3.2. Modified input parameters and data quality

Modified input parameters and resulting output para-

meters of the model are shown in Table 2 and the diet

matrix for the final run of the model is shown in Table 3.

Ecotrophic efficiencies (EE) were high for most func-

tional groups, whilst respiration/assimilation ratios (R/

A), production/respiration ratios (P/R) and net food

conversion efficiencies were within the expected range

-

(Christensen et al., 2004). Minimum biomass required

for the balanced model was larger than surveys for most

of the demersal and benthopelagic functional groups, of

which initial biomasses were assessed by the swept area

method, and suggested some undersampling in surveys.

Initial biomasses of some medium and large pelagic

Table 2

Modified input parameters and output parameters form the South Catalan Sea model

Functional group TL Bf P/Q EE F M2 M0 F/Z OI NE R/A P/R FD Q

1 Phytoplankton 1.00 10.20 – 0.83 0.00 31.56 6.35 – 0.00 – – – 64.72 –

2 Micro and Mesozooplankton 2.05 9.86 0.43 0.66 0.00 13.75 7.12 – 0.05 0.53 0.47 1.15 166.59 481.71

3 Macrozooplankton 2.77 0.54 0.40 0.91 0.00 18.48 1.92 – 0.28 0.48 0.52 0.91 5.44 27.51

4 Jellyfish 2.83 0.39 0.27 0.22 0.00 3.00 10.87 – 0.26 0.31 0.69 0.44 6.19 19.64

5 Suprabenthos 2.11 0.05 0.15 0.93 0.00 7.46 0.59 – 0.10 0.21 0.79 0.27 0.74 2.62

6 Polychaetes 2.00 15.54 0.16 0.32 0.00 0.59 1.24 – 0.00 0.38 0.62 0.60 123.13 179.18

7 Shrimps 2.98 0.05 0.43 0.97 1.03 1.95 0.10 0.34 0.39 0.54 0.46 1.15 0.07 0.33

8 Crabs 2.89 0.15 0.44 0.97 0.96 1.09 0.06 0.45 0.43 0.56 0.44 1.25 0.15 0.72

9 Norway lobster 2.82 0.04 0.26 0.98 0.25 0.92 0.03 0.21 0.72 0.33 0.67 0.49 0.04 0.20

10 Benthic invertebrates 2.02 8.87 0.33 0.43 0.00 0.43 0.59 0.001 0.02 0.57 0.43 1.34 17.17 27.77

11 Benthic cephalopods 3.10 0.21 0.44 0.97 1.10 1.16 0.08 0.47 0.11 0.51 0.49 1.03 0.16 1.11

12 Benthopelagic cephalopods 3.67 0.20 0.08 1.00 0.20 1.85 0.01 0.10 0.29 0.12 0.88 0.14 1.86 5.30

13 Mullets 3.16 0.06 0.33 0.97 1.83 0.40 0.06 0.80 0.10 0.42 0.58 0.71 0.09 0.42

14 Conger eel 4.22 0.06 0.40 0.97 0.75 0.61 0.04 0.54 0.05 0.50 0.50 1.00 0.04 0.20

15 Anglerfish 4.39 0.05 0.40 0.98 1.33 0.04 0.02 0.95 0.22 0.50 0.50 1.00 0.04 0.19

16 Flatfishes 3.20 0.04 0.28 0.98 1.56 0.50 0.04 0.74 0.16 0.35 0.65 0.54 0.06 0.31

17 Poor cod 3.31 0.03 0.22 0.95 0.55 0.89 0.08 0.36 0.30 0.27 0.73 0.37 0.05 0.23

18 Juvenile hake 3.45 0.04 0.18 0.98 0.49 0.78 0.02 0.38 0.40 0.22 0.78 0.28 0.06 0.32

19 Adult hake 4.10 0.35 0.24 0.98 0.59 0.00 0.01 0.98 0.04 0.30 0.70 0.42 0.18 0.89

20 Blue whiting 3.40 1.17 0.11 0.98 0.15 0.50 0.01 0.22 0.17 0.14 0.86 0.16 1.40 6.93

21 Demersal fishes (1) 3.08 0.52 0.17 0.99 0.33 0.82 0.02 0.28 0.09 0.21 0.79 0.27 0.72 3.55

22 Demersal fishes (2) 3.01 0.03 0.14 0.83 0.25 0.58 0.17 0.25 0.01 0.17 0.83 0.21 0.04 0.18

23 Demersal fishes (3) 3.96 0.14 0.07 0.97 0.01 0.41 0.01 0.02 0.12 0.09 0.91 0.09 0.18 0.87

24 Demersal small sharks 3.68 0.06 0.08 0.90 0.10 0.28 0.04 0.25 0.34 0.10 0.90 0.11 0.07 0.32

25 Bentopelagic fishes 3.49 0.22 0.15 0.97 0.30 1.04 0.03 0.22 0.13 0.22 0.78 0.28 0.61 1.99

26 European anchovy 3.05 2.64 0.10 0.96 0.36 0.93 0.05 0.27 0.00 0.14 0.86 0.16 11.14 36.71

27 European pilchard 2.97 3.58 0.17 0.97 0.79 0.67 0.04 0.53 0.08 0.24 0.76 0.32 9.66 31.73

28 Small pelagic fishes 3.00 0.92 0.07 1.00 0.02 0.50 0.00 0.03 0.05 0.10 0.90 0.11 2.03 6.77

29 Horse mackerel 3.19 1.55 0.08 0.30 0.01 0.10 0.27 0.04 0.10 0.09 0.91 0.10 2.00 7.93

30 Mackerel 3.55 0.61 0.09 0.51 0.09 0.14 0.22 0.19 0.13 0.12 0.88 0.13 0.74 2.99

31 Atlantic bonito 4.06 0.27 0.08 0.13 0.04 0.00 0.30 0.13 0.92 0.10 0.90 0.11 0.32 1.19

32 Large pelagic fishes 4.19 0.12 0.26 0.72 0.31 0.00 0.12 0.72 1.02 0.33 0.67 0.49 0.05 0.20

33 Loggerhead turtle 2.54 0.03 0.06 0.07 0.01 0.00 0.14 0.07 0.41 0.08 0.92 0.08 0.02 0.08

34 Audouins gull 3.22 0.001 0.07 0.00 0.02 0.00 4.62 0.00 0.92 0.08 0.92 0.09 0.02 0.07

35 Other sea birds 2.19 0.001 0.06 0.33 0.02 1.47 3.07 0.00 0.35 0.08 0.92 0.08 0.02 0.07

36 Dolphins 4.33 0.03 0.01 0.28 0.02 0.00 0.05 0.28 0.09 0.01 0.99 0.01 0.08 0.39

37 Fin whale 3.81 0.36 0.01 0.00 0.00 0.00 0.04 0.00 1.00 0.01 0.99 0.01 0.46 1.50

38 Detritus 1.00 70.00 – 0.866 – – – – – – – – 0.18 –

39 Discards 1.00 0.38 – 0.508 – – – – – – – – 0.002 –

40 By-catch 1.00 0.002 – 0.000 – – – – – – – – – –

TL=Trophic level; Bf=final biomass (t km�2); P/Q=production/consumption ratio or Gross efficiency; EE=Ecotrophic efficiency; F=Fishing

mortality (years� 1); M2=Predation mortality (years� 1); M0=Other natural mortality (years� 1); F/Z=Exploitation rate; OI=Omnivory index;

NE=Net efficiency; R/A=respiration/assimilation ratio; P/R=production/respiration ratio; FD=Flow to detritus (t km�2 years� 1); Q=Con-

sumption (t km�2 years� 1).


fishes, which were estimated from neighbouring areas or

referred to the entire Mediterranean basin, were slightly

lower in the balanced model (Table A1).

The pedigree index of the model (0.670, Table 4), a

measure of the model quality, ranked within the highest

values when compared with other 50 previously con-

structed models for which pedigree values ranged be-

tween 0.164 and 0.676 (Lyne Morisette, Fisheries

Centre, UBC, personal communication). The sensitivity

analysis routine showed that by altering the input para-

meters of a functional group, the largest impact was on

the output parameters of the same functional group.

3.3. Trophic levels and flows

Results of the model showed that functional groups

were organized within four integer trophic levels (TL)

with the highest TLs corresponding to anglerfish, dol-

phins, conger eel, large pelagic fishes and adult hake

(Table 2). The remaining functional groups were classi-

Table 3

Diet composition matrix for the functional groups in the South Catalan Sea model

Prey Predator

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 19 18 17 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

1. Phytoplankton 0.65 0.15 0.10 0.08 0.05

2. Micro and

Mesozooplankton

0.05 0.65 0.70 0.10 0.15 0.02 0.31 1.00 0.92 0.94 0.70 0.28

3. Macrozooplankton 0.05 0.14 0.13 0.31 0.01 0.01 0.01 0.47 0.01 0.14 0.61 0.17 0.62 0.01 0.46

4. Jellyfish 0.05 0.05 0.01

5. Suprabenthos 0.15 0.03 0.03 0.22 0.14 0.02 0.04 0.03 0.01

6. Polychaetes 0.25 0.34 0.01 0.32 0.48 0.19 0.66 0.10 0.50 0.73 0.08 0.07 0.01 0.03 0.04

7. Shrimps 0.05 0.03 0.04 0.02 0.02 0.05 0.02 0.01 0.00 0.03 0.01 0.01

8. Crabs 0.01 0.01 0.04 0.10 0.17 0.06 0.01 0.04 0.07 0.01

9. Norway lobster 0.04 0.01

10. Benthic invertebrates 0.18 0.17 0.09 0.02 0.89 0.06 0.01 0.52 0.53 0.01 0.12 0.99 0.05 0.32 0.08 0.01 0.29

11. Benthic cephalopods 0.00 0.01 0.03 0.02 0.01 0.07 0.01 0.14 0.03

12. Benthopelagic

cephalopods

0.01 0.02 0.03 0.02 0.00 0.14 0.31 0.01

13. Mullets 0.02 0.01

14. Conger eel 0.17 0.01

15. Anglerfish

16. Flatfishes 0.07

17. Poor cod 0.01 0.01

18. Juvenile hake 0.10 0.01 0.01

19. Adult hake

20. Blue whiting 0.03 0.27 0.05 0.12 0.02 0.03 0.08 0.16

21. Demersal fishes (1) 0.01 0.12 0.43 0.08 0.06 0.03 0.13 0.01 0.07 0.02 0.02

22. Demersal fishes (2) 0.02 0.03

23. Demersal fishes (3) 0.01 0.09 0.01 0.01 0.04 0.01 0.01

24. Demersal small sharks

25. Bentopelagic fishes 0.23 0.02 0.01 0.14 0.05 0.06 0.01 0.05

26. European anchovy 0.32 0.22 0.02 0.35 0.10 0.02 0.06 0.27 0.15 0.19

27. European pilchard 0.21 0.57 0.35 0.05 0.23 0.02 0.31 0.01 0.01

28. Small pelagic fishes 0.03 0.24 0.09 0.12 0.02 0.19 0.03

29. Horse mackerel 0.07 0.10 0.06 0.01

30. Mackerel 0.07

31. Atlantic bonito

32. Large pelagic fishes

33. Loggerhead turtle

34. Audouins gull

35. Other sea birds 0.02

36. Dolphins

37. Fin whale

38. Detritus 0.30 0.15 0.15 0.89 1.00 0.20 0.27 0.48 0.98

39. Discards 0.01 0.02 0.01 0.01 0.01 0.02 0.01 0.01 0.01 0.29 0.38 0.37

40. By Catch

41. Import 0.40 0.40 0.40 0.02 0.60 0.50

Total 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00

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Table 4

Ecological indicators of the South Catalan Sea model related with community energetics, community structure, cycling of nutrients and information

theory

Statistics and flows

Sum of all consumptions 852.11 t km� 2 years� 1

Sum of all exports 61.27 t km� 2 years� 1

Sum of all respiratory flows 327.16 t km� 2 years� 1

Sum of all flows into detritus 416.91 t km� 2 years� 1

Total system throughput 1657.0 t km� 2 years� 1

Sum of all production 658.0 t km� 2 years� 1

Calculated total net primary production 386.68 t km� 2 years� 1

Total primary production/total respiration 1.18

Net system production 59.52 t km� 2 years� 1

Total primary production/total biomass 6.55

Total biomass/total throughput 0.04

Total biomass (excluding detritus) 58.99 t km� 21

Total transfer efficiency 12.60 %

Total catches 5.36 t km� 2 years� 1

Mean trophic level of the catch 3.12

Primary production required to sustain the fishery (from pp) 36.70 %

Primary production required to sustain the fishery (from pp+det) 41.99 %

Gross efficiency (catch/net p.p.) 0.014

Ecopath Pedigree index 0.67

Network flow indices

Throughput cycled (excluding detritus) 27.39 t km� 2 years� 1

Predatory cycling index (of throughput w/o detritus) 3.33 %

Throughput cycled (including detritus) 6.56 t km� 2 years� 1

Finn’s cycling index (of total throughput) 25.19 %

Finn’s mean path length 4.27

Finn’s straight-through path length (without detritus) 2.40

Finn’s straight-through path length (with detritus) 3.19

Connectance index 0.20

System omnivory index 0.19

Information indices

Ascendency 25.50 %

Overhead (Total) 5300.80 Flowbits

Overhead 74.50 %

Capacity (Total) 7119.30 Flowbits

Ai/Ci 26.30 %

Ai=Internal ascendency; Ci=Internal capacity.


fied between 3.96 and 3.0 for fish species, and between

3.0 and 2.0 for invertebrates, with cephalopods showing

TLs of 3.1–3.67; the lowest, by definition, were the

primary producers and detritus groups (TL=1). Europe-

an sardine showed TLb3.0 because it feeds partially on

phytoplankton.

TLs of fish species (see Tables A1 and A2 for a list of

scientific names) were in line with the lower range of

previous results for the Mediterranean (Stergiou and

Karpouzi, 2002) and lower than those from the Cantab-

rian Sea (Sanchez and Olaso, 2004). Trophic levels

obtained for dolphins, fin whales and demersal sharks

were similar to those previously recorded (Pauly et al.,

1998b; Cortes, 1999). However, the trophic levels of

seabirds and turtles were low because discards are as-

sumed to be a detritus group with TL=1, which under-

estimate the trophic level of these groups. Discards are

consumed by gulls, terns, shearwaters and storm-petrels

and are mainly composed of small pelagics and benthic-

demersal small fishes (Arcos, 2001). Various studies

focusing on seabird feeding ecology and trophic levels

have described the average TL of similar seabird species

to be between 3.5 and 4 (Hobson et al., 1994), while

marine turtles can reach TL between 3.3 and 3.6 (Mack-

inson et al., 2000; Guenette et al., 2001).

Fig. 8 schematically represents the Catalan Sea eco-

system flow diagram organized by its integer trophic

levels (TL) in the form of the Lindeman spine (Lindeman,

1942; Ulanowicz, 1986; Wulff et al., 1989; Libralato et

al., 2002), where primary producers and detritus are

Fig. 8. The South Catalan Sea ecosystem flow diagram organized by its integer trophic levels (TL) in the form of the Lindeman spine. Primary

producers (P) and detritus (D) are separated to clarify the representation (both with TL=I).

Fig. 9. The fate of total system throughput in percentage per integer

trophic level.


separated to clarify the representation (both with TL=I)

(t km�2 years�1). Most flows are within TL I, II and III,

while flows from TLN III are practically insignificant.

TL I (primary production and detritus) generated 49.4%

of the total system throughput (t km�2 years�1), the sum

of all flows within the ecosystem, followed by the TL II

(41.9%). The average transfer efficiency (TE=12.6%),

the fraction of total flows at each trophic level that are

either exported or transferred to other trophic levels

through consumption, was within the range of values

reported in the literature (Odum, 1971; Pauly and Chris-

tensen, 1995), i.e., on average lower for detritus (12.1%)

than for the primary producers (13.2%). Values of TE for

flows through TL II and TL III were high, both high-

lighting good coupling between zooplanktivorous and

detritivorous and their predators (Baird et al., 1991). This

could indicate that the ecosystem may be food limited

(Shannon et al., 2003). Fig. 9 represents the fate, in

percentage, of total system throughput per discrete tro-

phic level. High proportions of the throughput were

consumed by predators at TL I, followed by TL II and

TL III, aligned with results from TE values.

More than 80% of the total system throughput was

related to the pelagic domain, but important flows were

also related to benthic invertebrates.Moreover, in terms of

biomass (t km�2) (Table 2), the detritus, phytoplankton,

zooplankton and non-crustacean benthic invertebrate

groups were the dominant groups, followed by sardine,

anchovy and the remaining small and medium-sized

pelagic fish species. Much lower biomasses of demersal

target and non-target fish species were sustained. Ninety-

nine percent of the total production (t km�2 years�1) of

the system was by phytoplankton, zooplankton, non-

crustacean benthic invertebrates and small pelagic fish

groups; while 95% of the consumption (t km�2 years�1)

was concentrated within the detritus, phytoplankton,

zooplankton, non-crustacean benthic invertebrates and

small and medium-sized pelagic fish groups.

3.4. Summary statistics

The total system throughput, also an index of the

ecosystem size (Christensen and Pauly, 1993b) and the

ig. 10. Main partitioning of a) total consumption of production,

xcluding plankton and benthic invertebrates, by predators; and b)

tal consumption of fished organisms production by predators (in-

luding the fishery) (higher than 2%).


total system biomass (td km�2) (Table 4) were small

compared with other modelled ecosystems from up-

welling and temperate regions (e.g., Christensen and

Pauly, 1993a; Jarre-Teichman, 1998; Guenette et al.,

2001; Sanchez and Olaso, 2004). The ecological indi-

cators related to community energetics, community

structure, cycling of nutrients and information theory,

and the comparison of these with other previously

modelled ecosystems (e.g., Christensen and Pauly,

1993a; Christensen, 1995b; Jarre-Teichman, 1998;

Guenette et al., 2001; Sanchez and Olaso, 2004),

suggest that the South Catalan Sea ecosystem is at

an intermediate–low developmental stage sensu

Odum’s theory (Odum, 1969, 1971). For example,

the primary production/respiration ratio (Pp/R) indicat-

ed that there was more energy produced than respired

within the system; the primary production/biomass

ratio (Pp/B) was also high indicating a low level of

biomass accumulation within the system compared

with primary production. Moreover, the total system

biomass/system production ratio (B/P), described as an

indirect estimate of the average size of organisms

within the system (and assumed to increase with in-

creasing average size) (Christensen and Pauly, 1993b;

Christensen, 1995a), was medium in the ecosystem.

The system showed moderate-low rates of cycling and

a low connectance and system omnivory index.

3.5. Consumption

The analysis of the consumption (higher than 2%)

of production of the system, excluding plankton,

macrobenthos and detritus groups, highlighted the

importance of sardine and anchovy within the system,

followed by jellyfish and horse mackerel (Fig. 10a).

The relevance of gelatinous plankton in the consump-

tion of production in the NW Mediterranean Sea was

also an important feature of the Namibia ecosystem

(Heymans et al., 2004; Roux and Shannon, 2004),

where the proliferation of jellyfish appeared after the

collapse of sardine fisheries in the 1960–1970s. The

proliferation of some jellyfish species in the NW

Mediterranean since the 1980s has been also described

(e.g., Buecher, 1999).

The analysis of the consumption (higher than 2%)

of fished organisms (from functional groups 7 to 32)

by main predators within the ecosystem highlighted

the high impact of the fishery, followed by cephalo-

pods and some demersal and pelagic fish species (Fig.

10b). Seabirds consumed 14.2% of discards generated

in the area and marine turtles consumed the 5.9%

(Table 2).

F

e

to

c

3.6. Mortality

Concerning mortalities, the general results are in

accordance with the range of values from stock assess-

ment in the region (Lleonart, 1990; AAVV, 2002b),

where most of the groups showed high predation mor-

tality (Table 2). Juvenile hake and small pelagic fish

showed high levels of fishing and predation mortality,

while fishing mortality was very high for some demersal

target species such as conger eel, anglerfish, red mullet,

flatfishes or adult hake. Some invertebrate groups such

as benthic cephalopods and crabs also showed high

fishing mortality. The exploitation rates (F/Z), where

F is the fishing mortality and Z is the total mortality

(Table 2), showed particularly high values for some

target species, like the small pelagics, some demersal

fishes and hake. The exploitation rate of sardine was

higher than the recommended rate of 0.50 for sustainable

fisheries management (Patterson, 1992; Mertz and

Myers, 1998; Rochet and Trenkel, 2003). In addition,

the exploitation rates for demersal fishes were high, and

in the case of anglerfish, mullets and adult hake the rate

Fig. 11. The Mixed Trophic Impact analysis from the model. Impacted groups are placed along the horizontal axis and impacting groups are down the vertical axis. The bars indicate relative impact

(between 0–1) where positive impacts are above zero line and negative impacts are below.

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was higher than the recommended exploitation rate of

0.8 for groundfish stocks (Mertz and Myers, 1998;

Rochet and Trenkel, 2003).

3.7. Mixed trophic impacts

Direct and indirect interactions within the ecosystem

were analyzed by means of the mixed trophic impact

routine (MTI) (Fig. 11). The analysis showed that all

groups had a negative impact on themselves due to

within-group competition. Indirect impacts of predators

on the system could also be detected, as, for example, the

negative effect of sardine or anchovy on other small

pelagic fishes due to some extent of niche overlapping.

An increase of adult hake had a negative impact on

juvenile hake, probably due to cannibalism and compe-

tition for prey. Other indirect impacts in the form of

trophic cascades (Menge, 1995) could also be identified,

e.g., an increase of dolphins would have an indirect

positive impact on anchovy due to the decrease of

other anchovy predators.

Moreover, numerous functional groups in the model

were impacted by the groups at the base of the food web

such as phytoplankton, micro-, meso- and macro-zoo-

plankton, suprabenthos and benthic invertebrates. This

could be related to possible bottom-up predator–prey

interactions occurring in the ecosystem (Hunter and

Price, 1992). Small pelagic fishes also had a wide impact

on numerous functional groups of higher and lower

trophic levels, highlighting the importance of these

groups in the ecosystem and possible wasp-waist pred-

ator–prey interactions (Cury et al., 2000).

Competition interactions between functional groups

of similar trophic levels were revealed by the analysis of

the MTI routine. In addition, important demersal-pelag-

ic relationships were identifying within the system be-

tween demersal predators (e.g., adult hake or conger eel)

and forage fishes or between medium-sized pelagic

fishes (mackerel and horse mackerel) and benthic inver-

tebrates, indicating coupled pelagic-demersal interac-

Table 5

Ecological information characterizing the main fleets of the South Catalan

Fishing fleet Landings Discards

Trawling 2.17 0.23

Purse seine 2.61 0.14

Longline 0.17 0.01

Troll bait 0.03 0.00

Total 4.98 0.37

Landings and discards (t km�2 years�1); TLc=mean trophic level of the ca

sustain the fishery from primary producers (pp) and primary producers and

tions. This was also found to be an important feature

of the Namibian upwelling ecosystem after depletion of

its stocks due to industrial fishing and environmental

events, an important trend that appears to set this system

apart from other upwelling ecosystems (Moloney et al.,

2005), and one that is also characteristic of highly fished

temperate regions (Sanchez and Olaso, 2004).

The trawling fleet had the widest-ranging impact on

all ecosystem compartments and the largest impacts on

some demersal groups (Fig. 11). An increase of trawling

activity would negatively impact various benthic and

demersal groups, as well as dolphins and marine turtles,

mainly due to the decrease of their main prey and the

direct mortality associated with by-catch. However, it

would positively impact the suprabenthos, juvenile hake

and demersal fish (3), possibly due to top-down effects

or trophic cascades caused by removal of predators

(Christensen et al., 2004). The longline fishery had

large negative impacts on its main target species and

on its by-catch (marine turtles, dolphins and seabirds),

whilst it had positive impacts on anchovy, and other

small and medium-sized pelagic fishes mainly due to

predator removal. The purse seine and troll bait fisheries

also showed important impacts on their target species;

the former impacted dolphins and large pelagic fishes

due to removal of prey, whilst the latter had positive

impacts on prey species of removed predators. Fishing

activity also impacted seabird groups by increasing or

decreasing discard availability and through direct mor-

tality. On the contrary, cetaceans, seabirds and marine

turtles did not significantly impact fishing activity, in

contrast with recent published results (AAVV, 2002a).

3.8. Primary production required to sustain fisheries

and trophic level of the catch

Primary production required to sustain the fishing

activity at the 1994 level relative to the primary pro-

duction of the system (%PPR) was very high (Pauly

and Christensen, 1995), when taking into account both

Sea

TLc OI %PPR

(pp)

%PPR

(pp+det)

3.16 0.13 15.95 23.21

3.01 0.01 13.78 10.43

4.04 0.06 5.47 6.98

4.16 0.06 1.50 1.36

3.12 0.10 36.70 41.99

tch; OI=fleet omnivory index; %PPR=primary production required to

detritus (pp+det).

Table 6

Final catch/initial catch ratio (Cf/Ci) from Ecosim dynamic simulations a) under 10–20–30% increases in fishing effort (A); b) with environmental

forcing reducing prey availability of small and medium-sized pelagic fishes (B) by 10–20–30% over 10 years; c) both combined (under mixed flow

control, bottom-up control and wasp-waist control)

a) Fishing effort (A) 10% 20% 30%

Mixed Bottom-up Wasp-waist Mixed Bottom-up Wasp-waist Mixed Bottom-up Wasp-waist

European anchovy 1.1 1.09 1.05 1.2 1.18 1.08 1.3 1.27 1.08

European pilchard 0.98 1.07 0.8 0.93 1.14 0.62 0.87 1.2 0.46

Little pelagic fishes 1.14 1.1 1.17 1.3 1.21 1.34 1.46 1.31 1.53

Horse mackerel 1.09 1.09 1.09 1.18 1.19 1.17 1.28 1.29 1.25

Mackerel 1.07 1.09 1.04 1.14 1.17 1.08 1.2 1.26 1.11

Demersal catch 1.02 1.03 0.98 1.02 1.05 0.95 1.13 1.07 0.93

Total system catch 1.01 1.07 0.9 1.01 1.13 0.81 1 1.18 0.73

b) Environm. anomaly (B) 10% 20% 30%


European anchovy 0.97 1 0.8 0.93 1 0.54 0.88 1 0.27

European pilchard 0.96 1 0.83 0.92 1 0.62 0.85 1 0.39

Little pelagic fishes 0.96 1 0.87 0.92 1 0.7 0.85 1 0.51

Horse mackerel 0.98 1 0.93 0.96 1 0.86 0.93 1 0.79

Mackerel 0.97 1 0.91 0.93 1 0.82 0.89 1 0.73

Demersal catch 0.99 1 0.94 1 1 0.88 1 1 0.82

Total system catch 0.97 1 0.86 0.93 1 0.69 0.89 1 0.51

c) A combined with B 10%A / 10%B 20%A / 10%B 30%A / 10%B





Horse mackerel 1.07 1.09 1.02 1.16 1.19 1.1 1.25 1.29 1.17

Mackerel 1.04 1.09 0.95 1.1 1.17 0.98 1.16 1.26 1.02

Demersal catch 0.99 1.03 0.92 1 1.06 0.91 0.99 1.07 0.89

Total system catch 0.98 1.07 0.76 0.97 1.13 0.67 0.94 1.18 0.6

10%A / 20%B 20%A/20%B 30%A/20%B





Horse mackerel 1.04 1.09 0.94 1.13 1.19 1.02 1.22 1.29 1.08

Mackerel 1 1.09 0.86 1.12 1.17 1 1.11 1.26 0.93

Demersal catch 0.98 1.03 0.88 0.98 1.05 0.87 0.98 1.07 0.85


10%A / 30%B 20%A / 30%B 30%A / 30%B





Horse mackerel 1.01 1.09 0.86 1.1 1.19 0.93 1.18 1.29 1

Mackerel 0.95 1.09 0.77 1 1.17 0.81 1.05 1.26 0.85

Demersal catch 0.95 1.03 0.83 0.95 1.05 0.84 0.95 1.07 0.83



the primary producers (36.7%) and the primary produ-

cers and detritus together (41.9%) (Table 5). The trawl-

ing fleet was the most impacting fleet in terms of its

contribution to the total %PPR, followed by the purse

seine fleet. The importance of trawling increased con-

siderably when taking into account flows from detritus


due to the high proportion of detritivorous species

caught by this fleet.

Small pelagic fish (anchovy and sardine) dominated in

terms of catches (70.1%), with benthic cephalopods

(4.3%), adult hake (3.9%), blue whiting (3.2%), demersal

fishes (1) (3.2%), crabs (2.7%) and other demersal fishes

and invertebrates atmuch lower catch levels (Table 1). The

recorded mean trophic level of the catch was 3.12 (Table

5). This was similar to that obtained from direct calcula-

tions from fishing data from the Central Catalan coast in

1996 (TL=3.04, Tudela, 2000); slightly lower than that

computed for the Western Mediterranean in 1998

(TL=3.25, Pinnegar et al., 2003); and slightly higher

than that obtained for the whole Mediterranean basin in

1994 (TL=3.0, Pauly et al., 1998a). The trawling fleet

was catching organisms with lower but wider ranges of

TLs (with higher omnivory index), while the purse seine

was catching organisms with lower and narrow TLs

ranges, and longline and troll bait were focusing on

organisms with high and narrow TLs range (Table 5).

3.9. Temporal dynamic simulations

Results from simulations with the temporal dynamic

Ecosimmodule showed that fishing effects were larger and

major perturbations were propagated throughout the sys-

tem under a wasp-waist control situation, while the mixed

control situation showed intermediate results and under

bottom-up control fishing impacts and environmental forc-

ing were more limited and had shorter propagated effects.

Similar results had previously been achieved when explor-

ing fishing effects for the Southern Benguela (Shannon et

al., 2000). Table 6 includes the final catch/initial catch

ratios (Cf/Ci) resulting from 45 Ecosim simulations with

increases of both trawling and purse seine fishing effort

from 1994 to 2003, with a persistent environmental

forcing for 10 years and with both factors combined.

Results assuming a shorter environmental forcing (1 and

Fig. 12. Ecosim dynamic simulation. Final biomass/initial biomass ratio (B

under wasp-waist flow control for small pelagic fishes, 20% increase of fish

sized pelagic fishes trough a sustained environmental forcing. 1—Benthopel

small pelagic fishes; 6—European anchovy; 7—European pilchard.

5 years) (related with the other 90 simulations) are not

included because they were not reproducing observed

recent dramatic trends in both landings and pelagic

biomass in the area between 1994 and 2003. In general,

a 55% decrease in total landings (Cf/Ci=0.45), 70%

reduction in anchovy landings (Cf/Ci=0.30) and 72%

reduction in sardine landings (Cf/Ci=0.28) can be seen,

while demersal landings showed small fluctuations with

a decrease of the 18% (Cf/Ci=0.82) (Fig. 3).

It was not possible to fully reproduce the observed

trends in catch and biomasses by simulating either

increases in fishing mortality (assumed to represent in-

creased fishing effort) in the area from 10% to 30% for

different periods of time or an environmental forcing for

different periods of time under any of the flow control

scenarios (Table 6). However, dynamic simulations com-

bining both factors, an increase of 10% to 30% of fishing

effort and 20% of forcing function, under wasp-waist

control, allowed the reproduction of recent dramatic

trends in both landings (Table 6) and pelagic biomass

(Fig. 12) in the area between 1994 and 2003. For in-

stance, a 20% increase in fishing for 10 years in combi-

nation with a 20% forcing function negatively affecting

the interaction between small and medium-sized pelagic

fish and their prey groups would lead to a 47% reduction

in overall landings (Cf/Ci=0.53), a 69% reduction in

sardine catches (Cf/Ci=0.31) and a 52% reduction in

anchovy catches (Cf/Ci=0.48), while demersal catches

would have decreased by 13% (Cf/Ci =0.87). A 10%

increase in fishing mortality for 10 years in combination

with a 30% decrease in prey availability would lead to a

55% reduction in overall landings (Cf/Ci =0.45), a 75%

reduction in anchovy landings (Cf/Ci=0.25) and a 74%

reduction in sardine landings (Cf/Ci=0.26), while the

demersal fraction would have decreased by 17% (Cf/

Ci=0.83). Moreover, these simulations yielded biomass

levels of sardine lower than those for anchovy (Fig. 12);

this situation has been recorded, for the first time in the

f/Bi) through 1994–2003 for small and medium-sized pelagic fishes

ing effort and 20% decrease of prey availability of small and medium-

agic fishes; 2—Jellyfish; 3—Horse mackerel; 4—Mackerel; 5—Other


area, by the stock assessments carried out in 2003 (Quin-

tanilla et al., 2004; Torres et al., 2004).

These results are supporting the general perception

that there has been an increase of the real fishing effort in

the area due to the increase of fishing capacity of vessels

(Bas et al., 2003). It is also important to underline that

results from dynamic simulation showed that an increase

of fishing effort would not translate into increased

catches (Table 6) under mixed nor wasp-waist flow

control situations; on the contrary, a decrease in catches

is predicted as fishing effort increases. Only small

increases in catches are predicted under bottom-up

flow control, even when the forcing function is not

included in the simulation. This would be in line with

the highlighted intense exploited status of the ecosystem

described and its resulting fragility.

4. Conclusions

The present model constitutes the first mass-balance

model constructed to characterise shelf and upper slope

exploited ecosystems from the western Mediterranean

Sea and it represents an important effort to integrate the

available biological data from the area in a coherent

format. Deficiencies in available biological data have

been identified. Further efforts to better characterise key

elements of the ecosystem, such as the trophic niche of

sardine and medium-sized pelagic fishes within the west-

ern basin, could be an important step forward towards the

characterisation of the ecosystem. Data is also scarce for

cephalopods and benthopelagic fishes, macrozooplank-

ton, suprabenthos and gelatinous zooplankton. More-

over, the incorporation of ontogenetic studies in

assessments would also be appropriate to increase the

quality of the model, as Mediterranean catches are par-

tially supported by recruits of target species (Lleonart and

Maynou, 2003; Sarda et al., 2005). Thus, although the

pedigree index of the model was high and the sensitivity

analysis proved the robustness of the model, the contin-

uous incorporation of new empirical data from the region

into the model would improve its results.

The ecosystemwas dominated by the pelagic domain,

which accounted for the main biomass and catches and

where flows mainly occurred. This ecosystem feature,

with the dominance in terms of biomass and catches of

small pelagic fishes (sardine and anchovy) and the pos-

sible wasp-waist predator-prey interactions, along with

the importance of hake and horse mackerel, are features

that usually characterise upwelling ecosystems (Jarre-

Teichman, 1998; Cury et al., 2000; Shannon et al., 2003;

Heymans et al., 2004; Moloney et al., 2005). However,

the studied ecosystem was limited by production (high

TE and EE values) and both primary production and

detritus were intensively used within the system. On

the other hand, benthic invertebrates had a higher im-

portance within this ecosystem than within typical up-

welling systems (Shannon et al., 2003; Heymans et al.,

2004; Moloney et al., 2005) or Atlantic ecosystems

(Sanchez and Olaso, 2004). Important pelagic–demersal

interactions were identified, and are a common feature of

highly fished areas (Moloney et al., 2005; Sanchez and

Olaso, 2004). The important role of gelatinous jellyfish

in the ecosystem was also highlighted.

Zooplankton and benthic invertebrates were identi-

fied as playing key roles in the ecosystem functioning

related to bottom-up control, while small pelagic fishes

would be involved in wasp-waist control situations, as

reinforced by the outcomes of the dynamic simulations.

A marginal top–down control of forage fish by predator

populations (e.g., dolphins and adult hake) within the

system was identified. This is in agreement with the long

history of fishing activity in the region that would have

strongly reduced the biomass of top predators to low

levels (Bas et al., 1985), resulting in the fishing fleets

acting as top predators in the ecosystem.

The ecotrophic efficiencies and mortality rates sug-

gested that the ecosystem is highly constrained by predators

(natural predators and the fishery). Although the predation

mortality was high for most of the groups of the model as

has been proved to occur in marine ecosystems even under

heavy fishing (Jarre-Teichman, 1998; Christensen and

Pauly, 1995), fishing mortality was very high for some

modelled groups, in agreement with results on growth

and recruitment overfishing of some demersal and pe-

lagic resources (Farrugio et al., 1993; Papaconstantinou

and Farrugio, 2000; Lleonart and Maynou, 2003; Bas et

al., 2003). At the same time, the intermediate-low devel-

opment of the ecosystem in terms of Odum’s theory of

ecosystem development (Odum, 1969, 1971; Christen-

sen, 1995a) was, at least partially, related to high fishing

intensity and further supported by a high gross efficiency

ratio, high primary production required to sustain the

fishery and the low trophic level of the catch (Pauly and

Christensen, 1995; Pauly et al., 1998a).

In addition, fishing impact per fleet indicated large

impacts on the principal components. Trawling was not

only the most non-selective gear and had the widest-

ranging impact on the different functional groups of the

ecosystem (important in terms of demersal biodiversity)

but it had the largest impacts on some demersal target

and non-target groups. The ecosystem impacts of the

longline fleet were especially important due to by-catch

of long-lived, slow-growing protected species; while

purse seines targeted high proportions of low trophic


level fishes that are main prey for top predators. On the

contrary, neither the consumption of fished production

nor the mixed trophic impact analysis suggests signif-

icant competition between vulnerable species (ceta-

ceans, seabirds and turtles) and fishing activity.

The assessment of non-reported landings was impor-

tant for many species, showing how the correction of

official statistics to include discards and IUU landings is

essential when placing fishing within the ecosystem and

assessing ecosystem status in theMediterranean Sea. For

instance, seabird dynamics were clearly influenced by

discard because it modifies their food supply, competi-

tion and predation interactions between species. The

model correctly captured positive and negative impacts

of discarding on seabird populations due to the direct

increase of food availability and to direct mortality,

respectively (Oro and Ruız, 1997; Oro et al., 1997;

Belda and Sanchez, 2001). Moreover, it could be seen

that discarding causes important changes in seabird

populations (Furness, 2003), where an increase or a

decrease in discards can be linked with both changes in

interactions between seabird species and with negative

effects on seabird biodiversity, as the larger species affect

the smaller ones, indirectly by competing for discards, or

directly through predation (e.g.,. Gonzalez-Solis et al.,

1997; Martınez-Abraın et al., 2003).

The low trophic level of the catch, characterising

Mediterranean ecosystems (Pauly et al., 1998a; Pinne-

gar et al., 2003) and ratified in the present study, is also

in line with the long history of exploitation in the

Mediterranean (Bas et al., 1985). However, the steady

decline in landings in the area from 1994 to 2003,

coupled with an important decline of pelagic biomass

within the system (Quintanilla et al., 2004; Torres et al.,

2004), is of special relevance and indicates the high

fragility of the ecosystem with respect to perturbations.

In fact, the application of a new index of ecosystem

impact of fishing based on the loss in secondary pro-

duction at higher trophic levels (Tudela et al., 2005;

Libralato et al., submitted for publication) suggested

that the fishing situation in 1994 signalled a high risk to

ecosystem overfishing sensu Murawski (2000), with

high probabilities of stock declines or collapses.

Moreover, dynamic simulations showed that a mod-

erate increase in fishing pressure from 1994 to 2003

synergistically coupled with a moderate forcing function

could reproduce the observed patterns of decreasing land-

ings and biomasses within the system when assuming

wasp-waist control. It was also shown that an increase in

fishing would not have been translated into an increase in

landings. These results highlighted the highly exploited

state of the present ecosystem and its low resistance, and

support the idea that the state of the resources in the

western Mediterranean Sea can dramatically change as

a consequence of fishing activities, in conjunction with

environmental forcing, and can lead to important changes

of the whole ecosystem (Farrugio et al., 1993; Lleonart

and Maynou, 2003), in contrast with the presumed

boverfishing steady stateQ of Mediterranean resources

(Caddy, 1997). Due to the key role that small pelagic

fish play within the system, decreases in pelagic biomass

would likely have important consequences on the whole

ecosystem structure and functioning (Cury et al., 2000;

Libralato et al., submitted for publication).

Although the Mediterranean basin is characterised by

marked heterogeneity in terms of ecological, geograph-

ical and also social and economical factors (Farrugio et

al., 1993), current results from the South Catalan Sea

model could be regarded as representative of other shelf

and upper slope regions of the western Mediterranean

and would imply the low resistance of these exploited

ecosystems and their inability to cope with synergistic

perturbations. In this context, ecological modelling can

be an important tool allowing the inclusion of trophic

interaction dynamics in the assessment and management

of marine resources within the context of the precaution-

ary approach and an adaptive management process. The

present model settles the basis to further develop dynam-

ic simulations in order to understand the extent to which

fishing activities, the environment and other anthropogen-

ic factors are driving marine resources in the area and to

describe the configuration of trophic interactions (Walters

et al., 1997; Christensen and Walters, 2004). The output

of different management strategies can then be studied.

Acknowledgements

This research was funded by the Spanish research

project CICYT.REN 2000-0878/MAR. During the

work M.C. was supported financially by a FPI follow-

ship from the MYCT of the Spanish Government. The

authors wish to acknowledge all those colleagues from

the Institute of Marine Science (ICM), the Centre for

Advanced Studies of Blanes (CEAB), the Mediterra-

nean Institute for Advanced Studies (IMEDEA) and the

Spanish Institute of Oceanography (IEO) that provided

essential data and technical advice for the development

of this work, with special mention to M. Carrasson with

her assistance on the analysis of trophic data and F.

Maynou for his continuous contributions and com-

ments. Moreover, they thank those scientific research-

ers from the Fisheries Centre (University of British

Columbia) that kindly supported the work and advised

on ecological modelling procedures with special men-

Appendix A

T le A1

In ut data and references by functional group for the South Catalan Sea Model

F tional group Original value Reference Observations

1. hytoplankton

B mass 0.4 mg Cl-a m�3

(10.2 t km�2)

Maso, 1989 Conversion factor used to transform units of

Cl-a m�3 to carbon units/m3 and organic matter

units/km2 from Jorgensen et al. (1991) and

Dalsgaard and Pauly (1997)

P 232 g C m�2 years�1

(37.91 years�1)

Tudela, 2000 Conversion factor used to transform carbon

units/m2 year to organic matter (Sorokin, 1990)

2. icro- and mesozooplankton

B mass 0.049 mgC dm�3

(9.86 t km�2)

Alcaraz et al., 2003;

Calbet et al., 2001

Dimensions of organisms between 53 Am to

5 mm. Data from 1996 and 2000

P 20.87 years�1 Pinnegar, 2000 Data modified to consider area’s temperature

(Opitz, 1996)

Q 48.85 years�1 Pinnegar, 2000 Data modified to consider area’s temperature

(Opitz, 1996)

T phic data Calbet et al., 2002 Indirect consideration of the microbial loop

taking into account the food intake of micro-and

mesozooplankton from the microbial food web

3. acrozooplankton

B mass 0.54 t km�2 Maynou et al., 2003 Dimensions of organisms N5 mm. Data

from 1998 to1999

P 20.41 years�1 Labat and Couzin-Roudy, 1996

Q 50.94 years�1 Baamstedt and Karlson, 1998

T phic data Baamstedt and Karlson, 1998;

Casanova, 1974

4. ellyfish

B mass 0.389 t km�2 Alcaraz et al., 2003 Dimensions of organisms N5 mm. Used

conversion factor to transform units of mgC/l

to g mo/m2 of 1.1 (M. Alcaraz. Pers. com).

P 13.87 years�1 Malej, 1989 Data from the Adriatic Sea corrected to consider

differences of temperature between areas

(Opitz, 1996)

Q 50.48 years�1 Malej, 1989 Data from the Adriatic Sea corrected to consider

differences of temperature between areas

(Opitz, 1996)

T phic data Orek, 2000

(continued on next page)

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ab

p

un

P

io

/B

M

io

/B

/B

ro

M

io

/B

/B

ro

J

io

/B

/B

ro

Table A1 (continued)

Funtional group Original value Reference Observations

5. Suprabenthos

Biomass 0.028 t km�2 Maynou et al., 2003 Maximum value weighted by bathimetric ranges

from 60 m, 150m and 200m depths. Data from

1998-1999

P/B 8.05 years�1 Cartes and Maynou, 1998

Q/B 52.12 years�1 Cartes and Maynou, 2001

Trophic data Cartes et al., 2001

6. Polychaetes

Biomass 15.54 t km�2 Sarda et al., 2000; Desbruyeres et al., 1973 Used conversion factor from dry weight to wet

weight of 15% (Rumohr et al., 1987)

P/B 1.83 years�1 Moodley et al., 1998 Data from the Adriatic Sea corrected to

consider differences of temperature between

areas (Opitz, 1996)

Q/B 11.53 years�1 Mackinson et al., 2000 Data from the Florida shelf corrected to


areas (Opitz, 1996)

Trophic data Fauchald and Jumars, 1979

7. Shrimps

Biomass 0.025 t km�2 Sarda, 1994, 2001; Lleonart, 2001 Biomass estimates from trawling surveys

(1994-2000) in the Catalan Sea

P/B 3.08 years�1 Marano et al., 1998 Data from the Adriatic Sea corrected to

consider differences of temperature

between areas (Opitz, 1996)

Q/B 7.20 years�1 Maynou and Cartes, 1998

Trophic data Cartes, 1991, 1993; Cartes et al., 2001

8. Crabs


(1994–2000) in the Catalan Sea

P/B 2.10 years� 1 M=Mackinson et al., 2000

Q/B 4.73 years� 1 Maynou and Cartes, 1998

Trophic data Cartes, 1991; Guerao, 1993

9. Norway lobster

Biomass 0.034 t km�2 Sarda, 1994, 2001 Lleonart, 2001 Biomass estimates from trawling surveys


P/B 1.20 years� 1 Froglia and Gramitto, 1988

Q/B 4.56 years� 1 Sarda and Valladares, 1990

Trophic data Cristo, 2000

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10. Benthic invertebrates

Biomass 8.873 t km�2 Desbruyeres et al., 1973; Sarda, 1994,

2001; Lleonart, 2001; Sarda et al., 2000

Biomass estimates from trawling surveys

(1994–2000) in the Catalan Sea. Complemented

from literature to include benthic macroinfauna

P/B 1.02 years� 1 Moodley et al., 1998 Data from the Adriatic Sea corrected to


areas (Opitz, 1996)

Q/B 3.13 years� 1 Pauly et al., 1993; Opitz, 1996

Trophic data Riedl, 1986.

11. Octopuses

Biomass 0.129 t km�2 Sarda, 1994; Lleonart, 2001; Sarda, 2001 Biomass estimates from trawling surveys


P/B 2.338 years� 1 Mackinson et al., 2000 Data from the Florida shelf model corrected to


areas (Opitz, 1996)

Q/B 5.3 years� 1 Amaratunga, 1983

Trophic data Sanchez, 1981; Quetglas et al., 1998

12. Squids

Biomass 0.139 t km�2 Sarda, 1994, 2001 Lleonart, 2001 Biomass estimates from trawling surveys


P/B 2.015 years� 1 Mackinson et al., 2000 Data from the Florida shelf model corrected to


areas with the equation of Opitz, 1996

Q/B 26.47 years� 1 Amaratunga, 1983

Trophic data Sanchez, 1982; Quetglas et al., 1999

13. Mullets



P/B 2.294 years� 1 Z=F+M; M=empirical equation from

Pauly, 1980

Q/B 6.90 years� 1 Empirical equation from Pauly et al., 1990

Trophic data Aguirre, 2000

14. Conger eel




Pauly, 1980


Trophic data Macpherson, 1981


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15. Anglerfish



P/B 1.58 years� 1 Z=F+M; M=empirical equation from Pauly, 1980



16. Flatfishes

Biomass 0.044 t km� 2 Sarda, 1994, 2001; Lleonart, 2001 Biomass estimates from trawling surveys



Pauly, 1980


Trophic data Macpherson, 1981; Tito de Morais, 1986;

Morte et al., 1999a

17. Poor cod





Trophic data Morte et al., 2001

18. Juvenile hake





Trophic data Bozzano et al., 1997, in press

19. Adult hake

Biomass


Q/B

Trophic data Bozzano et al., 1997, in press

20. Blue whiting




Pauly, 1980



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21. Demersal fishes (1)


994–2000) in the Catalan Sea



Trophic data Matallanas, 1980; Macpherson, 1981;

Rosecchi, 1983; Moreno and Matallanas, 1983;

Moreno-Amich, 1992, 1994, 1996;

Casadevall et al., 1994; Morte et al., 1999b


Biomass 0.013 t km� 2 Sarda, 1994, 2001; Lleonart, 2001 iomass estimates from trawling surveys










Trophic data Macpherson, 1981; Matallanas, 1982; Scotto di Carlo

et al., 1982; Zander, 1982; Stergiou and Fourtouni, 1991

24. Demersal small sharks





Trophic data Macpherson, 1980, 1981

25. Benthopelagic fishes





Trophic data Macpherson, 1981; Scotto di Carlo et al., 1982

26. European anchovy

Biomass 2.44 t km� 2 Palomera, 1995 iomass estimated from acoustic surveys

994) in the South Catalan Sea


Q/B 13.91 years� 1 Tudela and Palomera, 1995

Trophic data Tudela and Palomera, 1997


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(1

B

(1

B

(1

B

(1

B

(1

B

(1



27. European pilchard

Biomass 3.37 t km� 2 Palomera, 1995 Biomass estimated from acoustic surveys

(1994) in the South Catalan Sea



Trophic data Demirhindi, 1961

28. Small pelagic fishes

Biomass 0.69 t km� 2 Palomera, 1995 Biomass estimated from acoustic surveys

(1994 and 1996) in the South Catalan Sea



Trophic data Andreu and Rodriguez-Roda, 1951

29. Horse mackerel

Biomass 1.75 t km� 2 IFREMER. Non published data Biomass estimated from acoustic surveys

(1997) in the Catalan Sea

P/B 0.39 years� 1 Z=F+ M; M=empirical equation from Pauly, 1980


Trophic data Ben Salem, 1988; Kyrtatos, 1998a,b

30. Mackerel

Biomass 0.68 t km� 2 IFREMER. Non published data Biomass estimated from acoustic surveys

(1997 and 1999) in the Golf of Lion



Trophic data Moreno and Castro, 1995

31. Atlantic bonito

Biomass 0.3 t km� 2 Lleonart, 1990 VPA assessment from the Catalan Sea



Trophic data Moreno and Castro, 1995

Migration movements Sabates and Recasens, 2001

32. Large Pelagic Fishes

Biomass 0.14 t km� 2 ICCAT, 2003, in press



Trophic data Orsi Relini et al., 1995

Migration movements De La Serna and A lot, 1990; Block et al., 2001

M.Collet

al./JournalofMarin

eSystem

s59(2006)63–96

88

33. Loggerhead turtle

Biomass 0.32 t km� 2 Gomez de Segura et al., 2003 Data from visual surveys around the area.

Units of individuals/km2 has been transform

to T/km2 with the mean body weight per

specie (Merchan and Martınez, 1999)

P/B 0.15 years� 1 Mackinson et al., 2000 Data modified to consider area’s temperature

with an empirical equation (Opitz, 1996)

Q/B 2.54 years� 1 Polovina, 1984 Data modified to consider area’s temperature


Trophic data Tomas et al., 2001

Bycatch Caminas, 1988; Aguilar et al., 1995;

Caminas and De la Serna, 1995

34. Audouins gull

Biomass 0.0011 t km� 2 Oro and Ruız, 1997; Oro, 1999 Data from visual surveys around the area.



specie (Del Hoyo et al., 1992)

P/B 4.64 years� 1 Pinnegar, 2000 Data modified to consider area’s temperature


Q/B 70.0 years� 1 Nilsson and Nilsson, 1976

Trophic data Oro et al., 1997

Bycatch Belda and Sanchez, 2001; Tudela, 2004

35. Other sea birds

Biomass 0.0011 t km� 2 Aguilar, 1991; Oro and Ruız, 1997; Oro, 1999 Data from visual surveys around the area.

Units of individuals/km2 has been transformed


specie (Del Hoyo et al., 1992)

P/B 4.56 years� 1 Pinnegar, 2000 Data modified to consider area’s temperature


Q/B 73.20 years� 1 Nilsson and Nilsson, 1976

Trophic data Bosch et al., 1994; Oro, 1996; Granadeiro

et al., 1998; Arcos, 2001

Bycatch Belda and Sanchez, 2001; Tudela, 2004

36. Dolphins

Biomass 0.03 t km� 2 Forcada et al., 1994; GRUMM. 2002.

Non-published data.

Data from visual surveys around the area.

Units of individuals/km2 has been transformed


specie (Carwardine and Camm, 1998)



Q/B 13.49 years� 1 Innes et al., 1987; Trites et al., 1997

Trophic data Wurtz and Marrale, 1993; Blanco et al., 2001

Bycatch Tudela, 2004


M.Collet

al./JournalofMarin

eSystem

s59(2005)63–96

89



37. Fin whale

Biomass 0.39 t km� 2 Forcada et al., 1993 Data from visual surveys around the area.



specie (Carwardine and Camm, 1998)



Q/B 4.11 years� 1 Innes et al., 1987; Trites et al., 1997

Trophic data Pauly et al., 1998b

Migration movements Grannier, 1998

38. Detritus

Biomass 70. 0 t km� 2 Puig and Palanques, 1998 Used conversion factor to transform units

of carbon units to organic matter

(Parsons et al., 1977)

IFREMER=Institut Francais de Recherche pour l’Exploitation de la Mer.

GRUMM=Marine Mammal Research and Conservation Group (University of Barcelona, Spain).

M.Collet

al./JournalofMarin

eSystem

s59(2006)63–96

90

Table A2

Code Scientific name

Antomeg Antonogadus megalokynodon (Kolombatovic, 1894)

Aspicuc Aspitrigla cuculus (Linnaeus, 1758)

Aspiobs Aspitrigla obscura (Linnaeus, 1764)

Callmac Callionymus maculatus (Rafinesque-Schmaltz, 1810)

Caprape Capros aper (Linnaeus, 1758)

Ceporub Cepola rubescens (Linnaeus, 1766)

Chimmon Chimaera monstrosa (Linnaeus, 1750)

Chloaga Chlorophthalmus agassizii (Bonaparte, 1840)

Coelcoe Coelorhynchus coelorhynchus (Risso, 1810)

Deltqua Deltentosteus quadrimaculatus (Valenciennes, 1837)

Diplann Diplodus annularis (Linnaeus, 1758)

Eutrgur Eutrigla gurnardus (Linnaeus, 1758)

Gadiarg Gadiculus argenteus (Guichenot, 1850)

Gnatmys Gnathophis mystax (Delaroche, 1809)

Gobibuc Gobius bucchichi (Steindachner, 1870)

Gobinig Gobius nige (Linnaeus, 1758)

Helidac Helicolenus dactylopterus (Delaroche, 1809)

Hymeita Hymenocephalus italicus (Giglioli, 1884)

Lepicau Lepidopus caudatus (Euphrasen, 1788)

Lepicav Lepidotrigla cavillone (Lacepede, 1810)

Lepilep Lepidion lepidion (Risso, 1810)

Lesufri Lesueurigobius friesii (Malm, 1874)

Macrsco Macroramphosus scolopax (Linnaeus, 1758)

Maurmue Maurolicus muelleri (Cocco, 1838)

Molvdip Molva dipterygia (Rafinesque, 1810)

Myctpun Myctophum punctatum (Rafinesque, 1810)

Notabon Notacanthus bonapartei (Risso, 1840)

Ophibar Ophidion barbatum (Linnaeus, 1758)

Ophiruf Ophichthus rufus (Rafinesque, 1810)

Pageaca Pagellus acarne (Risso, 1829)

Pagebog Pagellus bogaraveo (Brunnich, 1768)

Pageery Pagellus erythrinus (Linnaeus, 1758)

Phycble Phycis blennoides (Brunnich, 1768)

Pomaspp Pomatoschistus spp. (Canestrini, 1861)

Scornot Scorpaena notata (Rafinesque, 1810)

Serrcab Serranus cabrilla (Linnaeus, 1758)

Serrhep Serranus hepatus (Linnaeus, 1758)

Spicspp Spicara spp. (Linnaeus, 1758)

Tracdra Trachinus draco (Linnaeus, 1758)

Tracsca Trachyrincus scabrus (Risso, 1810)

Triglas Trigloporus lastoviza ( Brunnich, 1768)

Triglyr Trigla lyra (Linnaeus, 1758)

Zeusfab Zeus faber (Linnaeus, 1758)

Epigden Epigonus denticulatus (Dieuzeide, 1950)


tion to S. Heymans. They also thank E. Morello and

L.J. Shannon for constructive comments on the draft

manuscript.

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