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Floating aquaculture cages
Floating aquaculture cages
FAO/2537/D.Marotiana

Most inland capture fisheries that depend exclusively on natural production are exploited above or close to their sustainable maxima and as a result global inland capture fisheries production is increasing only at a slow rate. Increasing pressure on the fishery resources, environmental degradation of aquatic habitats and poor fisheries management have contributed to this situation. Conventional fisheries management measures such as regulation of minimum mesh sizes, closed areas and closed seasons are used to counteract this situation, but these measures can be difficult to enforce and do not always offer the possibility to increase or maintain production levels in situations of high fishing pressure or in degraded environments. In such cases, techniques that can be collectively termed as enhancements are used. Enhancements are activities to raise productivity of selected species above natural levels. They include various possibilities to intensify fishery production. These possibilities are:

  • Introduction of new species to exploit under-utilised parts of the food chain or habitats not colonised by the resident fauna;
  • Stocking natural waters to improve recruitment, bias fish assemblage structure to favoured species or maintain productive species that would not breed naturally in the system
  • Fertilization to raise the general level of productivity and hence growth of the fish
  • Engineering of the environment to improve levels of reproduction, shelter, food resources and vital habitat; This also includes the establishment of sanctuaries to protect endangered fish species, to use the protected stock for enhancement and to protect the genetic purity of selected fish species
  • Elimination of unwanted species that either compete with or predate upon target species
  • Constituting an artificial fauna of selected species to increase the degree of control and the yield from the system
  • Modification of water bodies to cut off bays and arms to serve for extensive and intensive fish ponds to increase control and nutrient flows
  • Introduction of cage culture and parallel intensification of effort of the capture fishery
  • Aquaculture through management of the whole system as an intensive fish pond
  • Genetic modification to increase growth, production, disease resistance and thermal tolerance of the stocked or cultured material

Introductions and stocking that are the most commonly used techniques are mainly applied to lakes, reservoirs and rivers. There exist also a large number of small water bodies such as village ponds, and small irrigation tanks that have potential for enhancement. Stocking of fish in these smaller water bodies has been generally more successful because these are easier to manage, do not require large amounts of stocking material and are often more productive. In contrast, introductions of new species with the aim to establish self-reproducing populations (auto-stocking) have been more effective to enhance fisheries in the larger water bodies.

In general, the techniques chosen depend on the attitude of societies at different levels of economic development. The range of enhancement techniques involves increasing levels of human input and control that raise productivity significantly but also raise costs. The objective of many developed countries' stock enhancement programmes is to correspond to the preferences of sport fishermen or to maintain a quality of life and a fishery profession that is of historical significance but is being threatened by the various processes that make the country "developed". More recently, aquatic resource use is becoming increasingly subordinated to conservation. In developing countries, however, there is a large food deficit, especially of animal protein, and inland fisheries are being called upon to maximize supplies for human consumption. This leads to the increased use of enhancement techniques. In many cases, there is a close integration between capture and culture through extensive and semi-intensive management of artificial water bodies and rice paddies.

Sound environmental assessment of the potential impacts of the various enhancement techniques to be used under the given circumstances must be carried out prior to any intervention to make enhancement environmentally compatible and acceptable.

 
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