1 CONSERVATION OF AQUATIC ENVIRONMENT INTRODUCTION: What is a resource? Resource may be defined as a basic or primary material of the earth’s environment, which neither is manufactured nor processed product. Natural resource is often considered as a cultural appraisal. Because of the heterogeneity of human cultures, the value of resource may vary considerably in time and space. Categories of resource: Two categories of natural resources are renewable and non-renewable. (1) Renewable resources are living or biotic resources and other such as air, water and soil which are closely associated with and affected by living organisms. (2) Non-renewable resources are the non-living materials, minerals, fuels and similar things. The basic inherent distinction between these categories of resources is that renewable resources are able to reproduce or replace themselves or increase. For the renewable resources, management involves, as a minimum, practices that will result in a sustained yield. With proper forest management, trees can be cut every year, and yet there will always be trees in the future. With good soil management, land will always be able to grow agricultural crops. One can leave a breeding stock of a renewable resource and expect that with proper care it will generate the original supply. Improper use will results in impairment or exhaustion with adverse socio- economic consequences to man. Renewable resources are very much interrelated. For example, if a forest is cut and proper management practices are not followed, not only the timber is affected but also soil, climate, water regime, stream flow, fish life in water and animal life in Dr. Subhendu Datta Sr. Scientist CIFE, Kolkata Centre India
Stratagies to conserve aquatic environment from fisheries resources point of view is discussed. Conservation of fisheries resources and fish genetic resources are also described....
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CONSERVATION OF AQUATIC
ENVIRONMENT
INTRODUCTION:
What is a resource?
Resource may be defined as a basic or primary material of the earth’s environment,
which neither is manufactured nor processed product. Natural resource is often considered as a
cultural appraisal. Because of the heterogeneity of human cultures, the value of resource may
vary considerably in time and space.
Categories of resource:
Two categories of natural resources are renewable and non-renewable.
(1) Renewable resources are living or biotic resources and other such as air, water and soil
which are closely associated with and affected by living organisms.
(2) Non-renewable resources are the non-living materials, minerals, fuels and similar things.
The basic inherent distinction between these categories of resources is that renewable resources
are able to reproduce or replace themselves or increase. For the renewable resources,
management involves, as a minimum, practices that will result in a sustained yield. With proper
forest management, trees can be cut every year, and yet there will always be trees in the future.
With good soil management, land will always be able to grow agricultural crops. One can leave a
breeding stock of a renewable resource and expect that with proper care it will generate the
original supply. Improper use will results in impairment or exhaustion with adverse socio-
economic consequences to man. Renewable resources are very much interrelated. For example,
if a forest is cut and proper management practices are not followed, not only the timber is
affected but also soil, climate, water regime, stream flow, fish life in water and animal life in
Dr. Subhendu Datta
Sr. Scientist
CIFE, Kolkata Centre
India
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land are adversely affected. Virtually living resources are so intimately connected together
forming a system that when you touch one you touch them all.
The non-renewable resources can neither regenerate nor replace themselves. Once these
are used, they are gone and there is no hope for replacement. In such cases either we will have to
find a suitable substitute or do without it. For non-renewable resources, good management is
chiefly wise use with the avoidance of waste. It is possible to string out the supply for a longer
period and to use the resource only for worthwhile purposes, but if it is used at all, it will
eventually disappear.
A broad environmental approach to conservation is a necessity because physical
environment, biotic resources and the people form the whole.
What is conservation? From the foregoing discussion, conservation is thereby defined as the management of
human use of the natural resources so that it may yield the greatest sustainable benefit to present
generation while maintaining its potential to meet the needs and aspirations of future generations.
Conservation embraces preservation, maintenance, sustainable utilization and restoration of
natural environment.
NEED FOR CONSERVATION OF FISHERIES RESOURCES (threats to aquatic biodiversity)
The aquatic ecosystems have been subjected to various forms of environmental stress,
during the past few decades. Most of such environmental problems are man induced and not
normal. Some of such problems are discussed below:
(1) Anthropogenic activities: Increased human activities in the catchment area of the various
aquatic systems have affected the natural processes of the systems adversely thereby threatening
the normal growth of biotic communities. This is the main cause of all other problems. Changing
land use patterns with increasing demographic pressure has been identified as a potential threat
to natural resources including aquatic systems.
(2) Water abstraction: Encroachment or abstraction of natural water bodies for various usage
such as agriculture, urban expansion, industrial growth and so on has become the order of the
day (Pl. see table 1).
Table 1. Water use (India) 2000 AD (in million cubic meter/year)
Uses Taken Consumed Returned
Irrigation 869 783 86
Power 150 5 145
Industry 35 10 25
Domestic 38 8 30
Total 1092 808 286
(Available water 1900 million cubic meter/year)
(3) Siltation: Siltation in natural water bodies is one of the major problems affecting the
biodiversity. Deforestation, intensive agriculture and other anthropogenic activities have
accelarated the pace of soil erosion causing higher rates of siltation. The resultant impact of (2)
and (3) is shrinkage in effective water area, both in terms of physical extension and water depth,
leading to stress on fish abundance and biodiversity. The original germplasm is available only in
river. Higher sedimentation of Ganga riverbed up to Patna from Haridwar due to deforestation in
the catchment areas reduces the productivity. The denuded catchment washing are responsible
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for textural deformities. Wetland ecosystems in the country are the worst sufferer and may be
cited as the best example. Siltation also results in destruction of natural spawning/breeding and
feeding grounds.
(4) Pollution: Water pollution has assumed a serious proportion in recent years affecting the
aquatic resources adversely, both physically as well as biologically. The natural water bodies
have been subjected to an indiscriminate ingress of domestic sewage, factory effluents, oil
spillage, waste heat and solid wastes. Agricultural runoff containing fertilizer and pesticides has
added to the complexities. The net out comes of such developments ends up in excessive nutrient
enrichments leading to Eutrophication and as a result impairment in biotic growth. Pollution also
affects adversely the migration, behaviour, many physiological processes, life cycle, disease
incidence, nutrition, food chain and genetic make up. It also affects fishing and fishery products.
Emergence of algal blooms or massive invasion of macrophytes is some of the symptoms
indicating habit imbalance and creation of unfavourable aquatic regime, non-conducive for
normal distribution of biota.
(5) Weed infestation: Presence of aquatic macrophytes in reasonable quantity provides stability
to an ecosystem. However, its excessive colonization assuming the status of weed is highly
detrimental to ecological balance and hence the aquatic biodiversity and fish abundance. In each
ecosystems locking of necessary nutrients in the hydrophytic chain takes place and the
phenomenon of survival for the fittest operates as a result of which many sensitive and fragile
organisms are either eliminated completely or at least become endangered.
(6) River course modification: Fish and their habitats are considerably affected by river valley
projects. The problems, which arise for fishery due to the construction of a reservoir, are
unfavourable physico-chemical conditions of water, unavailable food and feeing areas,
restriction of fish migration, destruction of spawning grounds, excessive growth of aquatic weeds
and change in the species composition of fish. The decline of hilsa fishery above Farakka barrage
is due to the higher pollution level in the middle stretch of Ganga and impaired migration due to
Farakka barrage.
(7) Irrational fishing: The fishery resource of riverine sector is being subjected to intensive
exploitation by traditional fishermen and other communities with disastrous consequences to the
biodiversity and fish abundance of the system. Due to the over-exploitation of the fish stock, fish
production of many river systems has decreased considerably. This along with various
destructive methods of fish catching e.g. use of unselective gears, catching of juveniles and
brooders, poisoning, dynamiting, electro fishing have resulted decreased fish abundance in the
conventional fishing grounds in inland open waters.
Example-1: Huge quantity of both commercial and non-commercial prawn and fish seed is being
destroyed (9139.5 to 19294.5 million in five months from February to June) during selective
collection of Bagda seed (P. monodon) from Sunderbans region. It is recorded that Bagda seed
constitute only 5-10% of the total catch of the nets.
Example-2: The indigenous carp L. fimbriatus and large catfish (M singhala and S. childreni),
which together contributed about 70 tones in 1963 reduced to insignificance due to over fishing
in Godavari river system.
(8) Introduction of exotic fish species: About 300 species of fishes have been introduced into
India for the development of sports and cultural fishery, control of weeds and aquatic insects and
for recreation. However, exotic fish species have been reported to affect the native fish fauna
adversely either directly or indirectly.
Direct effects:
Through predation: Example 1: Brown trout (Salmo trutta fario) introduced in Beas river
affected the snow trout (Scizothorax plageostomus) by predation, which was used to be major
fishery of the river.
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Example 2: In Punjab, Gambusia affinis, has reduced the population of many species as it has
natural tendency to feed on fish eggs and hatchlings.
Through competition for niche: Example 1: Introduction of silver carp in the Govindsagar dam is
responsible for drastic decline of catla catla, both being plankton feeder.
Example 2: Cyprinus carpio has also affected the Cirrhina mrigala due to common feeding
habit.
Example 3: In the Dal lake of Kashmir, C. carpio is attaining predominance over valuable
endemic mahseers and Schizothoracids, due to its early maturity, prolonged spawning period and
higher fecundity.
Example 4: Tilapia mosambica has wiped out most of the naturally occurring fishery of Puntius
spp, in the Amaravatty reservoir in Coimbatore district.
Both common carp and Tilapia spp also affect the culture fishery (in composite fish culture) due
to their prolific and wild spawning.
Indirect effects: (Through parasitism, niche modification and hybridization): Introduced fish
species may transfer and spread parasitic disease across the countries. In the lake Victoria, fish
introduction is reported to result in change in fish community, which ultimately caused
Eutrophication and algal bloom. Hybridization between exotic and native species has profound
effect on the genetics of original fish species.
(9) Insufficient legislation and willingness from Government: Legislations limiting effort,
declaring closed seasons and sanctuaries, regulation of mesh size and minimum size for catch
have not made any impact. Enforcing legislations in riverine fisheries is a daunting task for
obvious regions. Many fishermen communities are migrating with families from one place to
another in search of good fishing. Without the willing co-operative of fishermen, implementation
of various conservatory measures is extremely difficult. This is possible only with the
improvement of socio-economic conditions of fishermen community. They should be helped to
settle permanently at once place and weaned away from river fishing by providing alternate
avenues such as leasing the water bodies to them for reasonably long periods and developing
fisheries in tank and reservoirs. Present legislations on fisheries are not sufficient. For
management of fishery resources strong effective enforcement of existing regulation are needed.
However, most important is educating the user group of the resources and prosecutation should
be regarded as the best resort. The users of fisheries resources should be made familiar with
regulations and reasons for their imposition. However, all these things required good willingness
from Government, which is lacking at present.
All the above factors viz. water abstraction, deforestation leading to land and soil erosion,
pollution from domestic sewage and industrial effluents, intensive agricultural practices which
are responsible for sedimentation in river bed, weed infestation, eutrophication, destruction of
feeding and breeding grounds, river course modification, irrational fishing, insufficient
legislation and lack of willingness from legislator and politicians had led to the habitat
destruction of fishery ecosystem and thereby decline the fish abundance and fish production in
the conventional fishing grounds in inland open waters and pose severe threats to aquatic
biodiversity. All factors that are responsible for depletion of fishery resource are supposed to
intensify during 21st century. Such a scenario calls for proper management of fishery resources
without curtailing the economic growth. Hence, the need for conservation of fishery resources
arises.
CONSERVANCY MEASURES FOR RIVER AND RESERVOIR FISHERIES
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In view of the diverse nature of the perturbations causing degradation of inland fishery resources,
several strategies are adopted to stabilize the status of fisheries and to prevent their further
decline. These strategies include following measures:
1. Habitat manipulation
2. Fish population manipulation
3. Fishing regulation
4. Aquaculture
5. Research and monitoring
6. Public awareness
1. Habitat manipulation: It pertains to enhance the fish yield without actually increasing its
population or altering the community structure. It is required to provide favourable
environmental conditions in order to sustain fish life particularly of desirable species and to
increase the total carrying capacity of the water body. Habitat manipulation includes protection
and restoration/improvement of the habitat.
(a). Protection of the habitat: Native fish habitat can be protected by creating specific reserves
and refuges where habitat conditions are suitable for target species and which are protected from
further loss and degradation. Whenever possible, rivers should be protected from further
deterioration by checking development in the floodplains and catchment areas, dredging,
straightening and revetting of the banks of the main channels, siltation and disposal of untreated
sewage and industrial effluents.
(b). Restoration/improvement of the habitat: Lost or degraded habitat can be restored or
improved to increase fish abundance, diversity, and overall environmental quality. It involves the
management of water level and its flow, protection and improvement of water quality. In stream
habitat is improved by using devices that impound or modify the river flow (e.g. current
deflectors), provide cover and improve the spawning areas. Bank side environment (riparian
environment) of streams and rivers can be protected and restored by fencing the riverbanks to
prevent loss of vegetation through cattle grazing. Off channel habitats such as side channels,
back channels, ponds, marshes and wetlands, which are important habitat for fish, should be
recreated and restored.
Recreation of suitable hydraulic regime in the water bodies is also very important step for
the habitat improvement. In standing water bodies (ponds, lakes and reservoirs) water quality can
be improved by the application for fertilizers, control of aquatic vegetation, desiltation, aeration
etc. Large rivers are difficult to manage because of size, current and variations in discharge.
However, water quality can be improved through soil and water management in the catchment
area, treatment of domestic and industrial waters before their discharge and control of water level
by planned storage and release from reservoirs.
2. Fish population manipulation (Regulation of species): It pertains to the alterations in the
population density of fishes and their composition in the water body. It involves reduction of
existing population of undesirable fish species and stocking of individuals of new or already
established species.
(a). Population reduction: It is desirable when lake or pond becomes contaminated by species of
no value for angling or fish production. Even if this undesirable species are present in small
numbers, they are always a danger to the desirable fish species because of their prolific breeding
habits. Population of undesirable species is controlled through netting, trapping or electro
fishing. In cases, where these species are present in abundance and it is not possible to remove
them partially, then eradication of fish community is carried out by using toxicants, by draining,
or by both the methods.
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(b). Stocking: It is one of the most popular management techniques. It pertains to stocking or
introduction of fish in lakes and reservoirs where natural breeding has been restricted by dam
construction or where fishery are on the decline because of over fishing and poor water quality.
Stocking/introduction involves following practices:
Stocking of resident species to support existing stocks.
Introduction of species that might have been present but are threatened or eliminated by
anthropogenic activities.
Introduction of additional species native to the catchment area.
Introduction of additional species native to catchment area.
Introduction of exotic species to support or enhance its existing fishery
Creation of fish community in newly constructed or redeveloped water body.
Native fish translocation or introduction should be done carefully because it has adverse
ecological and genetic effects on the recipient native stock. No introduction should be carried out
where there is no apparent niche for the species. When a niche is vacant, the introduction of new
species can support large fisheries. In India, several indigenous fish species (Catla catla, Labeo
rohita, Cirrhina mrigala, Labeo kalbasu) have been transferred from one river system to another
in order to improve local fish fauna and to increase fish production.
3. FISHING REGULATION: Various methods are there to regulate the fishing such as:
(a). Mesh regulation: This implies the restriction on mesh size of the net. The use of mesh
selective gear usually entails a consideration of the mesh sizes to be adopted which can only be
viewed relative to the characteristics of the stock to be exploited. As has been described, the
fishing-up process usually involves a drift downwards in the mesh size, which needs
considerable enforcement of legislation to stop. If the objective of the fishery is to exploit only
the large species of the community, the imposition of mesh limits, which protect the immature
fish, is probably the only way to do it effectively. If the mesh size is lowered to take the
advantage of the smaller species, then almost automatically the larger ones will disappear. As
number of species caught increases progressively as the size of the mesh decreases. One possible
solution to the dilemma is the limitation of mesh size in major gears such as seine nets, gill nets,
etc. The minimum mesh size for nets permitted under Indian Fisheries act (1897) is 30 mm so
that smaller fish are not caught.
(b). Restriction on size of the fish to be caught: The minimum size of the fish to be caught
vary in different states from 225 to 305 mm so that every fish get a chance to breed at least once
in its lifetime. Restrictions are also imposed on the sale of undersized fishes.
(c). Restriction on types of gear (Gear regulation): Gear is often prohibited for reasons other
than those bearing directly on the fish stock. Long lines, for instance, are regarded with disfavour
by users of cast nets, which may become entangled in the hooks. Barriers, which completely
block the river channel, thus stopping fish migrations, are as likely to be removed for reasons of
navigation as for fisheries. However, there are restrictions on the type of gears to be used for
catching desirable individuals of commercial fishes. In Delhi, since 1948 restriction have been
imposed on fishing except with rod and line, hand line and long line from July 1 to August 30,
every year.
(d). Restriction on total catch: The total catch is related to the number of fishermen operating
on the river. Furthermore, the individual artisanal fisherman seems to have a limited fishing
power in that he is physically capable of removing only a certain quantity of fish from the system
in any one year. Because of this, the solution that seems most appealing in this type of fishery is
a simple restriction on the number of fishermen operating in a certain region. Such control of
access through licensing remains one of the most important managerial tools, particularly in
commercial or recreational fisheries. An allied technique, the fixing of catch quotas for
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individual fishermen poses enforcement problems in artisanal fisheries but may be practical
where industrialized practices which are more intensive are adopted.
(e). Closed season: This means restriction of fishing in certain periods. By nature, most river
fisheries have built-in closed seasons. In the floodplain this lasts from just after bank full on the
rising flood to peak floods when the fish population is too dispersed and individual fish are too
small in size for them to be readily available to the majority of methods of capture. In the
torrential upper reaches, flows are frequently too high for effective fishing during some of the
year. This effective closed season makes biological sense in that it allows the fish to reproduce
relatively undisturbed and for the young to grow to a reasonable size before they are exposed to
the fishery. However, restrictions on the overly heavy fishing of migrating adult fish to the
spawning grounds may be necessary in some places. Under Indian Fisheries act (1897), fishing is
prohibited during spawning season or during any season of poor quality of fish.
(f). Declaration of sanctuaries or protected waters: As fishing of the floodplain and river
channel in the dry season becomes more intensive, there is a risk of local over-exploitation of the
stock. For this reason, traditional fisheries have long been based on the designation of certain
floodplain depression lakes and reaches of the river as reserves, which remained unfished. In
larger systems, there are actually inaccessible areas, which from reserves as they are infrequently
exploited. As a management measure the conservation of certain areas is probably a wise move
and gains force when other pressure are being applied to the system. Under Indian Fisheries act
(1897), certain parts of the river and reservoirs, which constitute breeding and nursery grounds of
fishes are declared as sanctuaries and are closed for fishing for certain periods or all the year
round.
(g). Leasing of lakes and reservoirs in alternate years: This is done in order to give the fish
a chance to breed and to make up the natural stock of these water bodies.
(h). Prohibition on indiscriminate fishing: Fishing by means of fixed engines (fixed engine
means net, cage, trap or other contrivances fixed in the soil for tracing the fish) or construction of
weirs is prohibited.
(i). Ban on the use of explosives or poisonous substances: The restriction or complete
outlawing of fishing practices that are more destructive is most important. However, even such
methods may be appropriate in some circumstances. Poisoning of watercourse liable to damage
the stocks of fish when carried out in the main channel of the river, whereas its use for removing
fish from temporary floodplain pools or for eradicating undesirable species may be quite
permissible. Unfortunately was the use of poisons allowed in one habitat it would rapidly extend
to others. Under Indian Fisheries act (1897), for fishing use of explosives or poisonous
substances is prohibited [For details of the Indian Fisheries act (1897) and rules framed there
under in various states is given at the end of this chapter].
(4). Aquaculture: Aquaculture in lakes and reservoirs is the best way of utilizing the natural
resources, easing the pressure on capture fisheries and meeting the rising demand of fish.
(5). Research and monitoring: There is urgent need for more research on threatened fish
species to provide more information on their habitat needs, pattern of distribution and abundance
and various aspects of biology particularly breeding and developmental biology.
(6). Public awareness: Awareness should be created among general public, fishermen and
anglers about the value of native fishes, threats to fishes due to various human activities and
various adaptive measures to conserve the inland fishery resources.
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FISH BIODIVERSITY OF INDIA: PRESENT STATUS AND
CONSERVATION STRATEGIES
India is fortunate to possess vast and varied fish germplasm resources distributed widely in vivid
aquatic ecosystems. The aqua resources of the country include 2.02 million square Km area of
Exclusive Economic Zone (EEZ) of surrounding seas, more than 29,000 Km length of rivers,
about 1,13,000 Km of canals, about 1.75 million ha of existing water-spread in the form of
reservoirs, about 1 million ha in the form of tanks and ponds and about 0.6 million ha of
stagnant, derelict, swampy water-spread area.
What is biodiversity (Biological diversity)?
The most accepted definition, propounded at Rio Conference reads as:
“Biological diversity means the variability among living organism from all sources including
inter alia, terrestrial, marine and other aquatic systems and the ecological complexes of which
they are part; this includes diversity within species, between species and of an ecosystem”.
The definition in question suggests that biodiversity does not mean only the variability of
species and the conservation of threatened biota but it covers the whole range of natural
environment, from microbes to landscape. It is suggestive, therefore, that the conservation of
biodiversity must be viewed in its totality rather than restricting our observation to living ones
only.
Need for biodiversity: Maintenance of fish biodiversity along with the other biotic resources
can be viewed as prerequisite for the well being of even the human beings. While several reasons
can be ascribed to the need, there are four basic reasons for the maintenance of biotic resources:
1). Diversity or variability seems aesthetically pleasing in most environments. This is not only
true in general but often applies to the specific species frequently encountered by man.
2). There is often local pride in population or species that characteristic of an area. People often
become disturbed when some local form of animal is threatened by extinction and this concern is
an important region for conservation of at least some species.
3). It is generally agreed by ecologists and evolutionary biologists that species diversity and
genetic variability are necessary for the long-term maintenance of stable complex ecosystem and
species.
4). All the living being co-evolves for their mutual benefits during the evolutionary process in an
ecosystem. Any species getting extinct upsets the ecological balance to the detriment of each
species and community as a whole.
Indigenous fish biodiversity: About 2,200 finfish species have been recorded by the NBFGR
(National Bureau of Fish Genetic Resources), Lucknow form different ecosystems of India
which is 10% of the total fish species as more than 20,000 species (approx. 22,000 till date)
reported worldwide. Out of these 2200 species, about 400 species are commercially important
which includes cultured, culturable and wild species. The approximate break-up of fishes
inhabiting different ecosystems is given below:
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Table 2: Approximate break-up of fishes inhabiting different ecosystems
Ecosystems No. of fish
species
found
Percentage
of total
Examples
Cold water 73 3.32% Masheers, Trouts, Bolla, Kalabans etc.
Warm fresh water 644 29.27% Carps, Fresh water Catfishes,
Airbreathing fishes, Minnows etc.
Brackish water 43 1.50 % Mullet, Hilsa, Bhetki, Prawns etc.
Marine water 1440 65.45% Sardines, Marckerel, Bombay duck,
Tunas, Pomfrets, Marine water Catfishes,
Crustaceans, Molluucks, Pearl, Oysters,
Clams, Mussels etc.
Exotic fishes in Inland ecosystem: (a). Sport fishes: Brown trout, Rainbow trout, (b). Food