Ecosystem-based fishery management

Many of the world’s fish populations are overexploited, and the ecosystems that sustain them are degraded (1). Unintended consequences of fishing, including habitat destruction, incidental mortality of nontarget species, evolutionary shifts in population demographics, and changes in the function and structure of ecosystems, are being increasingly recognized. Fisheries management to date has often been ineffective; it focuses on maximizing the catch of a single target species and often ignores habitat, predators, and prey of the target species and other ecosystem components and interactions. The indirect social and economic costs of the focus on single species can be substantial. For example, over 90% of the annual mortality of white marlin, a species petitioned for listing under the U.S. Endangered Species Act, occurs through incidental catch in swordfish and tuna longline fisheries. This threatens a recreational fishing industry worth up to U.S.$2 billion annually (2). To address the critical need for a more effective and holistic management approach, a variety of advisory panels (3–9) have recommended ecosystem considerations be considered broadly and consistently in managing fisheries. Ecosystem-based fishery management (EBFM) is a new direction for fishery management, essentially reversing the order of management priorities to start with the ecosystem rather than the target species. The overall objective of EBFM is to sustain healthy marine ecosystems and the fisheries they support. In particular, EBFM should (i) avoid degradation of ecosystems, as measured by indicators of environmental quality and system status; (ii) minimize the risk of irreversible change to natural assemblages of species and ecosystem processes; (iii) obtain and maintain long-term socioeconomic benefits without compromising the ecosystem; and (iv) generate knowledge of ecosystem processes sufficient to understand the likely consequences of human actions. Where knowledge is insufficient, robust and precautionary fishery management measures that favor the ecosystem should be adopted. We need to derive and develop community and system-level standards, reference points, and control rules analogous to singlespecies decision criteria (10–12). We may want to ensure that total biomass removed by all fisheries in an ecosystem does not exceed a total amount of system productivity, after accounting for the requirements of other ecosystem components (e.g., nontarget species, protected species, habitat considerations, and various trophic interactions). Maintaining system characteristics within certain bounds may protect ecosystem resilience and avoid irreversible changes. EBFM must delineate all marine habitats utilized by humans in the context of vulnerability to fishing-induced and other human impacts, identify the potential irreversibility of those impacts, and elucidate habitats critical to species for vital population processes. Protecting essential habitat for fish and other important ecosystem components from destructive fishing practices increases fish diversity and abundance (13, 14). Thus, ocean zoning, in which type and level of allowable human activity are specified spatially and temporally, will be a critical element of EBFM. The impacts of fisheries on endangered and protected species, including ecological processes that are essential for their recovery, should be managed through an EBFM approach. Single-species management has been successful at reducing incidental catch of protected species in some cases(e.g., with turtle excluder devices in trawls), but EBFM would also manage indirect effects (e.g., protecting forage fish near sea lion rookeries). Another goal of EBFM is to reduce excessive levels of bycatch (i.e., killing of nontarget species or undersized individuals of the target species), because juvenile life stages and unmarketable species often play important roles in the ecosystem (15, 16). Globally, discards in commercial fisheries have been estimated at 27.0 million metric tons, accounting for about one-fourth of the world’s marine fish catch (17). Bycatch problems can be ameliorated through ocean zoning that would prohibit use of nonselective or destructive gear in critical areas, as well as through the development and deployment of more selective and less damaging fishing technologies.