Fish Resources; Threats and Protection

Abstract

The status of fish species and fish resources is reviewed. Actual and potential threats are identified and, as far as possible, quantified in terms of their potential to cause local or general extinction. Excessive depletion by fishing alone has rarely, if ever, caused extinction, but the circumstances in which unrestrained fishing could potentially do so are identified. The harm to fish arising from deterioration of water quality caused by toxic pollutants and acidification is well documented and, for the most part, well understood. More subtle and potentially more dangerous conditions arise from excessive organic enrichment in low-energy systems such as deep lakes and semi-enclosed seas, which may lead to the creation or enhancement of an anoxic layer and its spead into shallower regions. The majority of introduced fish species have proved either non-viable or ecologically neutral. A small proportion have been beneficial, mainly in man-made water bodies. Some, notably general colonisers and powerful predators, have seriously harmed the native fish fauna. Most serious, because the fish have little or no natural protective response, is disruption of water flow or loss of habitat. Significant loss of genetic diversity can be caused even when these factors are not so serious as to cause total extinction. In reality, it is usual for two or more of the above threats to operate together; it is shown how the result may be more dangerous than the sum of their independent effects. In conclusion, it is suggested that a more rigorous and uniform definition of threat is needed. The established criteria and methodology of risk assessment could be used with advantage. Complete protection, except in special circumstances, is unattainable. A better strategy is to intensify efforts to convince the users of fish resources, whether for food, sport or the aquarium trade, that sustainable harvesting is to their long-term advantage as well as that of the fish. Above all, the need is to convince the general public that the conservation of fish is just as important as that of other more visible fauna and flora.