Interaction Between Fishery Management and Environmental Protection

Abstract

Assessment of the need to take account of fishery and environmental parameters in management depends on the precision with which it is possible to predict fishery yields from fishery and environmental data. Earlier attempts to demonstrate simple correlations of yield with various fishing and environmental indices were frustrated by variability in statistical data, poor definition of oceanographic and population systems, and ignorance of the responsible mechanisms. Recent research has overcome some of these difficulties. The results support earlier hypotheses that environmental fluctuations are major factors controlling year-class success. There is also evidence for strong density-dependence of survival of larval fishes, and of growth in juveniles and adults, all of which tend to stabilize population production under a wide range of environmental and fishery "stresses." There is recent evidence, however, that in some populations, effects of the recent and highest sustained rates of fishing have exceeded the "adaptative" capacity of the production-compensating mechanisms so that the carrying capacity of the environment is now unsaturated. There is thus a higher probability that a "normal" succession of "poor" years will lead to fishery collapse. While we do not understand why the effects show in certain species and areas and not in others that are equally heavily fished, there can be little doubt of the reality of these symptoms of interaction of fishing and environmental effects.The main mechanism controlling fishery productivity fluctuations within areas appears to be the degree of vertical mixing in oceanographic systems, with the associated nitrogen supplies and food resources for the early life-history stages of fishes. There still exist major unexplained differences between areas in the structure of the producing communities and the yields from them. Explanation will require detailed study of particular areas. In parts of the Northwest Atlantic, it appears that the control of production is geographically sited along the coastlines, where the risk of concentrations of pollutants also appears highest. In other areas, such as the Northeast Atlantic the oceanographic processes underlying production may be different.Assessment of the risk of pollution concentration, and its importance in reducing density-dependent compensatory production responses, is still frustrated by high-frequency variability in samples of both biological and physical parameters. Recent studies have demonstrated that this variability may be associated with particular types of generating mechanisms and suggest means for interpreting it. Further research in this area is required before meaningful environmental and biological monitoring programs can be undertaken.Recent knowledge of natural variability, and its interaction with density-dependent mechanisms controlling production, implies that a new approach involving "discontinuous" models appears necessary to prediction of ecosystem responses to fishing and pollution. But whatever their precise form, it is now clear that both the predictive models and the management systems built upon them, must necessarily take account of both fishing and environmental quality parameters if the management is to be effective.