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close this bookEnvironmental Handbook Volume II: Agriculture, Mining/Energy, Trade/Industry (GTZ, 1995, 736 p.)
close this folderAgriculture
close this folder32. Fisheries and aquaculture
View the document1. Scope
View the document2. Environmental impacts and protective measures
View the document3. Notes on the analysis and evaluation of environmental impacts
View the document4. Interaction with other sectors
View the document5. Summary assessment of environmental relevance
View the document6. References

2. Environmental impacts and protective measures

2.1 Artisanal small-scale fisheries

The actual fishing activities have the greatest bearing on the environment, as the long-term availability of the resources depends on the extent to which these activities are geared to the resource situation and to the conditions prevailing in the ecosystem fished. Through centuries of experience, traditional artisanal small-scale fisheries based in a specific location have made sure that they do not over-fish the available resources. Any attempt to increase production can jeopardise this well-established equilibrium.

It may nevertheless be possible to increase production without endangering the resources. Such an opportunity exists in cases where the stocks fished are utilised at a level below that guaranteeing optimum yield and sustainability. The same applies if fishing activities are extended to those components of the biocoenoses within the ecosystem that were previously utilised very little or not at all.

However, utilisation of additional species may be limited by the food relationships between various components of a biocoenosis. If the prey of a predatory fish starts to be utilised in addition to the fish itself, the potential yield that can be derived from the predatory fish is automatically reduced, as the food supply has been curtailed. Since many such relationships exist, it is essential that they should be carefully reflected in the management models if it is intended to simultaneously utilise a variety of different organisms within a single ecosystem.

In management of fishery resources, a key role is played by the nature of the gear used as well as by when and where it is used. Modern fishing gear can be highly efficient (i.e. may jeopardise the existence of stocks if no restrictions are imposed on its use) and highly selective. Fishing gear is considered selective if it catches only particular species or size categories of organisms. Its selectivity can be determined by net mesh size, hook size, or the depth of water or depth zone in which it is used. The most important fishery management measures include closed seasons, protected areas, minimum mesh and hook sizes, limits on the number of sets of gear, boats or ships and on the times when they may be used, and stipulation of catch quotas and size categories for the organisms to be caught.

Stock management calls for a high level of training in fishery biology and adequate knowledge of fishery economics. Stock regulating measures should be discussed, agreed upon and implemented by the local fishermen acting on a collective basis.

Apart from the need to conserve the resources themselves, it is also essential to protect their living environment against influences that could raise problems in the short or long term; to this end, the physical, chemical and biological condition of fishing areas must be monitored. Product quality depends on the chemical and biological conditions of the water and on the sanitary conditions prevailing ashore (village hygiene). The destructive effects of using wood resources for smoking fish can be curbed in two ways: by employing energy-saving kilns which permit more rational use of wood and by ensuring appropriate management of the forest resources concerned. The amount of wood required for boat-building can be reduced by replacing dugout canoes with boats made of planks and by using alternative construction materials.

Where it is likely that infrastructure for landing places used in artisanal fishery can be modified or removed only with difficulty, such facilities should not be constructed unless their necessity and expediency have been thoroughly reviewed. Concrete structures can also mar the aesthetic value of their surroundings (tourism).

2.2 Small-scale aquaculture

Aquaculture offers considerably greater options than capture fishery as regards both the type of organisms to be produced and the production sites. The natural stocks of organisms suitable for aquaculture can be most effectively conserved if aquaculture controls the entire life cycle, beginning and ending with the reproductive stage, and does so not just for one or two generations but on a long-term basis. As yet, however, this is possible only in the case of a few aquatic organisms. The only way of overcoming this problem is to promote applied basic research in the fields of reproductive physiology and reproductive ecology.

The production site should be chosen with the aim of conserving natural ecosystems and scarce water resources. The choice of the type of organism to be produced can contribute to conserving heavily used food resources if preference is given to species whose food requirements can be met by waste products or by-products from other sectors. Such products can either be fed directly to the fish or be used to fertilise the water and thereby promote the multiplication of food organisms (algae, microfauna). This could, for example, reduce demand for fish meal as a constituent of fish food. However, producers have a tendency to concentrate on expensive organisms (e.g. certain species of predatory fish) which generally require food of extremely high quality.

Water quality within and downstream of an aquaculture facility is determined by management practices. Efforts must be made to ensure that as little leftover food as possible remains in the water and that the quantities of nutrients and pollutants washed out of the installation are kept to a minimum. The amount of leftover food can be minimised by gearing the quantities of food given and the frequency of feeding to the absorption capacity and appetite of the fish. If sizeable quantities of waste are nevertheless discharged (e.g. from intensively operated through-flow ponds), they can be caught in settling ponds and thus largely prevented from entering rivers and lakes.

Drugs for preventing and treating disease and for combating parasites should not be used in running water (through-flow ponds) for reasons of effectiveness and economy and should not be used at all in open systems (cages, pens), even if the fish then have to be transferred to special containers for treatment and are thereby exposed to stress situations.

The main way of saving energy in aquaculture is to obviate the necessity of pumping for the purpose of water renewal. Introducing new water benefits the oxygen supply and helps to wash out wastes, besides compensating for evaporation and seepage losses. The extent of the necessary water replacement depends largely on the stocking density. Pumping energy can be saved wherever natural gradients can be used to create a water flow. Artesian springs are sometimes also available.

Considerable ecological advantages are offered by ponds in which wastes can be utilised by plants and microfauna which for their part are suitable as food for productive aquatic organisms. Such ponds can be fertilised by livestock (poultry, pigs) kept above or next to them. The profitability of this type of integrated aquaculture depends on the ecological appropriateness of the aquatic organisms kept, their popularity with consumers, the production costs and market prices. A role is also played by the way in which aquaculture is integrated into the overall production system, which usually involves other forms of production requiring labour. It is important, however, to know what constitutes the basis of the microfauna's food supply (there is a risk that pesticide residues could find their way into the food chain).

When setting up ponds in tropical countries, it is essential to bear in mind the risks originating from diseases whose pathogens spend at least one stage of their life cycle in water or in aquatic organisms (malaria, schistosomiasis etc.).

Cage farming not only involves high feeding costs, but also gives rise to problems in procuring the necessary materials for making the cages, as nets, support rods and floats are expensive. Only in forested regions is the use of wood unlikely to present any problems.

Elimination of potential health risks attaching to consumption of aquaculture products must be given particular attention wherever human excrement and domestic wastewater are used for fertilising ponds. In wastewater aquaculture systems, the critical factors in this respect are the number of pond stages, the degree of dilution and the period for which the water is retained before it enters the fish ponds. Accurate management, along with regular checks on sanitary conditions and water quality, are essential in such cases.

2.3 Use of artificial lakes in fisheries and aquaculture

As use of artificial lakes involves a combination of fish farming and fishing (and can thus be placed in the category of "culture-based capture fisheries"), the environmental protection measures described in both 2.1 and 2.2 above are of relevance in this connection. However, the fact that an artificial lake is a man-made entity creates a substantially different situation, both in limnological and ecological terms as well as from the sociological and economic viewpoints. Man-made lakes

differ from natural ones by virtue of their artificial nature, the fact that they are subject to continuous management to enable them to fulfil their primary purposes (drinking-water supplies, energy generation, irrigation), their initial biological "void" which - depending on the actual and to some extent random sequence of colonisation by flora and fauna - can offer scope for a variety of biological development possibilities, and last but not least the new options which this may offer in terms of fisheries and aquaculture. While an artificial lake thus allows man a considerable degree of freedom in shaping ecological conditions, it nevertheless confronts him with far-reaching social and economic problems when it comes to developing and establishing the ways in which it is to be used.

Two important principles should be observed when determining how a new artificial lake is to be used:

- Organisms that are foreign to the ecosystem and region concerned should be introduced only with strict observance of internationally recognised precautionary measures or not at all.
- No attempt should be made to regulate fishery activities until local traditions have been studied in detail; regulation measures should be realised in consultation with existing local fishermen and those willing to settle in the area.

When a new dam is being planned, consideration should be given to the various options for fisheries and aquaculture which the newly created lake will offer. Where appropriate, such aspects should be taken into account when deciding on dam design.

2.4 Fishery in the 200-mile exclusive economic zone

Optimum fishing of the 200-mile exclusive economic zone (EEZ) calls for use of advanced technology. This will inevitably lead to conflicts in the transition area between industrial deep-sea fishing and artisanal inshore fisheries unless depth conditions and coastline configuration create a natural division between the two. Such conflicts are often to the detriment of the available resources, causing them to be over-exploited or even destroyed. They may also adversely affect the economic and social position of the artisanal inshore fishermen, who usually come off worst in such conflicts if their interests are not effectively safeguarded through government intervention.

While old-established, traditional fishing communities have developed fishing practices designed to ensure that resources are preserved in the long term, the technical potential of modern deep-sea fishing - which can totally exhaust resources within a short time - means that use of resources must be strictly limited and monitored. Minimum mesh and hook sizes must be laid down to make sure that the gear does not catch young organisms which are not yet mature enough to reproduce and thereby preserve the existence of the fish stocks. Such regulations can also reduce the pointless destruction of small food organisms caught in the nets together with the fish.

The only way to prevent trawls with "ploughing" structures from causing serious damage to entire communities of sea-bed organisms is to ban the use of such gear. Depending on local conditions (sea-bed conditions, reproductive cycle and migration of fish or other organisms), use of such nets must be banned either completely, or in specific areas or at certain times of year.

Complete bans must be imposed on catching certain types of organism while they are still going through their development phase in the "nursery areas". As such bans are often impossible to enforce, efforts are being made in many places to create artificial refuges - in the form of submerged concrete blocks, for example - to which fish and other aquatic organisms can retreat and from which they can repopulate areas which have been subject to adverse influences or whose stocks have been exhausted. However, the effectiveness and cost-benefit ratio of these "artificial reefs" are still the subject of considerable debate.

The death of numerous fish and large marine fauna (dolphins, turtles, birds etc.) in lost drift nets made of plastic that does not decompose in water can be prevented by using degradable thread to attach the net sections to the floats. The net sections would then collapse after a time and sink to the bottom. However, this method appears to be too complicated for general use and it is not known what damage the nets might cause on the sea bed.

Considerable problems are still posed by the question of what to do with the "by-catch" (of non-target species), in other words the organisms with little financial value that are caught together with the highly lucrative species (e.g. prawns or shrimps) constituting the intended catch. These organisms are large or bulky enough to be retained by the net together with the main catch even if the minimum mesh sizes are adhered to. However, their market value is so low by comparison with that of the main catch that it is not worthwhile landing them, despite the fact that a considerable proportion of this "by-catch" would often be suitable for human consumption. If a worldwide solution to this problem could be found, for example by having the by-catch continuously collected by special boats at sea or by means of other methods, several million additional tonnes of fish would become available as food each year.

As is generally the case with motorised seagoing shipping, deep-sea fishing vessels' high consumption of fossil fuel necessitates special measures to dispose of residues on land. Environmental problems on land as a result of fishing stem primarily from industrial processing of the catch. Mandatory standards regarding disposal of solid wastes and wastewater must be observed; in some places such standards have still to be introduced. Some of the solid wastes can be made into fish meal, while valuable constituents of liquid waste can be recovered in the form of extracts and used as feed additives (cf. environmental briefs Inland Ports, Shipping on Inland Waterways, Wastewater Disposal and Solid Waste Disposal).

2.5 Use of mangrove swamps in fisheries and aquaculture

The traditional ways of using the flora and fauna in mangrove swamps can be viewed in the same light as artisanal small-scale fisheries in other areas: they take into account the regeneration capacity of the resources and are thus ecologically sound. However, this is not true of modern aquaculture on large fish farms whose construction necessitates complete clearance of the mangrove vegetation. One example of this type of operation is the large-scale raising of brackish-water prawns. As production of these much sought-after crustaceans can yield high profits, the potential suitability of mangrove swamps as sites for brackish-water ponds has given rise to dangerous pressure on these areas. Since mangrove areas are subject to the daily ebb and flow of the tide, the water has the necessary salt content and water replacement can be achieved at relatively little expense because the tidal cycle can be used to minimise the amount of energy required for pumping.

Efforts should be made to counter the pressure on the mangrove swamps in as realistic and flexible a manner as possible. The paramount principle should be that no form of use is to be permitted without thorough advance planning. The principal purpose of such planning is to completely rule out non-traditional use of areas which are irreplaceable as nature reserves, genetic resources, nursery areas for important aquatic organisms or protective belts guarding against coastal erosion. Clearance of mangrove swamps for the purpose of aquaculture can also be prevented by making areas immediately upstream of the mangrove belt available for the creation of ponds. Provided that the installations are well-managed, the necessary pumping costs could be offset by earnings.

Where use of mangrove swamps appears unavoidable for economic reasons, activities should be concentrated in areas with clayey soils. In such areas the mangrove vegetation can easily re-establish itself if the ponds (or swamp-rice fields) are abandoned at a later date, whereas areas with sandy and peat soils will be nothing more than wasteland for a long time afterwards. Continuing efforts should also be made to find ways of utilising the natural productivity of suitable mangrove areas for semi-intensive small-scale aquaculture, without clearing them of all vegetation

and without major additional expenditure on feed or fertiliser. The success of such experiments will depend on whether or not it proves possible to keep costs down to a level ensuring that even low yields per unit of area offer attractive economic prospects.