CONCEPTS AND ISSUES IN MARINE ECOSYSTEM MANAGEMENT

Ecosystem management means different things to different people, but t he underlying concept is similar to that of the long-standing ethic of conservation. Current interest in marine ecosystem management stems f rom concerns about overexploitation of world fisheries and the perceiv ed need for broader perspectives in fisheries management. A central sc ientific question is whether the effects of harvesting (top down) or c hanges in the physical environment (bottom up) are responsible for maj or changes in abundance. Historically, ecology, fisheries biology, oce anography, fisheries management and the fishing industry have gone som ewhat separate ways. Since the 1980s, increasing attention has been gi ven to multispecies aspects of fisheries, the linkages between oceanog raphy and fish abundance and more holistic approaches to fisheries man agement. Sorting out the causes and effects of fluctuations in fish ab undance is complicated by the lack of reliability of fisheries statist ics. Discards, dishonesty and the inherent logistic difficulties of co llecting statistics all combine to confuse interpretation. The overcap acity of fishing fleets and their unrestricted use are widely recogniz ed as a contributing cause to overfishing and declines in fish stocks in many parts of the world. Ecosystem management, as shorthand for mor e holistic approaches to resource management, is, from a fisheries man agement perspective, centred on multispecies interactions in the conte xt of a variable physical and chemical environment. Broader perspectiv es include social, economic and political elements which are best cons idered pragmatically as a part of the context of fisheries management. Objectives in marine ecosystem management are varied. From a biologic al perspective, an underlying principle of management is commonly assu med to be a sustained yield of products for human consumption. Whether that should be taken to mean that the yield should always be of the s ame products is less certain. Fishing commonly changes the relative ab undance of species of fishes. Thus, a biological objective should spec ify the species mix that is desired. Concern for the maintenance of gl obal diversity has generated a substantial literature on threatened an d endangered species. In general, it has not been considered likely th at marine fish species could be rendered extinct and greatest attentio n has been given to marine mammals, sea birds and sea turtles. The pro vision of marine parks and sanctuary areas are obvious first steps in providing a measure of protection, at least for the less widely rangin g species. Related to the current concepts of ecosystem management are expressions such as ecosystem health and ecosystem integrity which ar e given a wide range of different meanings, none of which are readily translated into operational language for resource management. These an d similar expressions are best assessed as rhetorical devices. The ess ential components of ecosystem management are sustainable yield, maint enance of biodiversity and protection from the effects of pollution an d habitat degradation. Theory for marine ecosystem management has a lo ng history in fisheries and ecological literature. Ecological models s uch as Lotka-Volterra equations, ECOPATH, trophic cascades and chaos t heory do not give practical guidance for management. Fleet interaction and multispecies virtual population analysis models hold more promise for fisheries managers. Alaska provides particular opportunities for developing new concepts in fisheries management. Statistics of catch a re good, stock assessments are at the state-of-the-art level and manag ement has been prudent. Debate is active on the causes of substantial changes in abundance of many species including marine mammals, because substantial changes in the fisheries have been accompanied by major c hanges in oceanographic conditions. As elsewhere, the resultant change s may be a consequence of top-down and bottom-up effects. The bottom p art is beyond human control, and ecosystem management is centred on ma naging the top-down or fisheries component in the context of special m easures of protection for particular species. Whether that is a realis tic goal depends in part on how much special protection is to be affor ded to which species. Marine mammals, for example, are given high prio rity for special protection, but like fisheries they too may have sign ificant roles in shaping the structure of marine ecosystems. Eventuall y, ecosystem management must come to grips with the question of how mu ch protection of particular species is desirable in achieving optimal use of living marine resources.