the incidental catch by fishing gear of adult and juvenile fish that are not the target of the fishery (Alverson et al., 1994). Bycatch and habitat loss not only may have deleterious effects on fishery yields, but also may degrade the ability of marine ecosystems to support biological diversity. Therefore, effective regulation of fishing activity in the oceans is not just a fishery management issue. For example, unique features and habitat such as coral reefs need prohibitions on fishing, as well as protection from shipping, diving, recreational boating, and destructive coastal development. Ecosystem approaches, including marine reserves, will have to be added to the conventional management toolbox to conserve biodiversity, maintain biocomplexity, and ensure that ecosystem services are maintained for posterity. The public's interest in ecosystem approaches in part represents the existence values that the public places on preserving the diverse biota and habitats of the sea (see Chapter 4). To ensure the future of living resources and habitats in many stressed marine ecosystems, some areas of the ocean could be zoned in MPAs for limited access and use. This chapter describes conventional fishery management tools, noting both limitations and failures, to provide a context for evaluating MPAs and reserves as complementary or alternative tools.
In general, conventional fishery management seeks to maintain high, yet sustainable, yields by regulating the number or weight of fish caught, the size of fish caught, or the time and space (area) within which fishing is allowed. The intent in each case is to control fishing mortality rates. Conventional approaches to fishery management in the United States can be succinctly characterized by three main components: (1) an underlying fishery science and management paradigm, (2) a set of conventional management tools, and (3) the fishery management system.
Fishery management relies on estimates of the population size of a target species to determine how many fish or what fraction of the population's biomass can be caught without damaging its reproductive potential. To make these determinations, management depends on a conceptual model of a fishery that makes three simplifying assumptions: (1) the fishing fleet targets and exploits a single-species stock, (2) the stock of interest is segregated temporally or spatially from other stocks, and (3) the individuals are perfectly mixed so that the effects of fishing are well spread over the whole stock. These assumptions, which are far from true in most situations, can have serious consequences for the effectiveness of fishery management.