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1588 of living aquatic resources, and thus ensuring ecosystem sustainability. Our definition focuses. on overall objectives that are ecosystemic. However, typical conservation activities focus on populations of single species without direct reference to ecosystem consequences. This is partly because such pop- ulations are usually more obvious and easier to study than communities, landscapes, or genes (Noss 1990). As Magnuson (1976) noted, interactions between populations (e.g., predation and competition) form the heart of the functional aspects of community ecology. Without a reliable methodology that can be applied directly at the ecosystem level, population-based conservation may be the most prac- tical way "to begin to cope with the issue of whole system viability" (Soule 1987). Significant, but indirect, protec- tion for the entire ecosystem may be provided by actions designed to preserve the viability of populations that fill key functional roles in the system. This approach, founded on such familiar concepts as keystone predators, indicator organisms, and integrator species may be the most effective way currently available to achieve ecosystem sustainability. A population-level focus is particularly applicable to fisheries management because human exploitation of fish resources has traditionally focused on populations of par- ticular species, which tend .to be managed in isolation. What modern conservation ideas demand from manage- ment practice is explicit consideration of the ecosystem context that underlies the sustainability of any population (Andrewartha and Birch 1984). Classical practice treated an exploited population as an isolated entity, cut off from its past (i.e., its evolutionary history and consequent genetic heterogeneity), and independent of the abiotic and biotic components of its supporting ecosystem. Modern practice must explicitly recognize the essential roles that all of these components play in determining the sustainability of indi- vidual populations, and consequently of entire ecosystems. The particular importance of genetic heterogeneity to management practice has been the focus of much recent work (Allendorf and Ryman 1987; Ryman and Utter 1987; Hindar et al. 1991). Such considerations, embodied under the rubric of the stock concept, now playa significant role in many fisheries management actions. Stocks are repro- ductively isolated subunits of populations that may, over time, become genetically differentiated. If the number of stocks involved in a fishery and their relative abundance is not known, the possibility of overfishing will always exist (see Loftus and Regier 1972, for examples drawn from North American Great Lakes fisheries). Even if stock com- position is known, allowable harvests must be kept well below values considered as optimal given the history of fisheries exploitation (Larkin 1977; Peterman 1977; Ludwig et al. 1993). In the long term, population sustainability requires stock sustain ability and thus stock-specific man- agement. For all of the reasons outlined above, we have made fish stocks the primary focus of the principles espoused in this paper. Fundamental principl~ The primary goal of fisheries management is to ensure the perpetuation of self-sustaining stocks of indigenous aquatic Can. J. Fish. Aquat. Sci. Vol. 52, 1995 species and, where possible, to allow their sustainable use. A commitment to resource maintenance is essential to pre- serve the biological base for such use. The principle can be stated as . aquatic ecosystems should be managed to ensure long-term sustainability of native fish stocks. Despite efforts to shift the focus of fishery management from species' stocks to multispecies assemblages, most fish- ery management practice is still stock oriented (Mercer 1982). In an evaluation of New Zealand's approaches to conserva- tion, Towns and Williams (1993) argue that species-, or stock-, oriented approaches must be viewed as comple- mentary to community- or guild-oriented and habitat-oriented approaches. Rich (1939) foresaw that conservation and reha- bilitation of salmon (and we would argue other species), if it were to be successful, would have to occur at the stock level. Thus, the key to conservation is sustainability of nat- urally reproducing wild stocks of native fish. These stocks embody thousands of years of evolutionary adaptations to local environments. The unique biological suitability of native stocks to their resident water bodies ensures that they are best able to withstand significant human use with- out serious deterioration in their long-term sustainability. These small, spatially isolated stocks are important guar- antors of the genetic diversity of a species. In particular, stocks that occur in marginal habitats that may be active sites of natural selection may be of adaptive significance to the species as a whole (Scudder 1989; Northcote 1992). The role of hatcheries and stocking in conservation must be re-evaluated. Hatchery programs intended to sup- plement existing wild, native stocks may have the opposite effect. The artificial selection process in hatcheries favours domestic, as opposed to wild, traits. Subsequent inbreeding with wild !;tocks can quickly undo thousands of years of natural selection and lead to loss of local stocks (Nehlsen et al. 1991; Hilborn 1992). Recruitment overfishing of wild stocks, stimulated by the planting of hatchery fish, can have the same effect (Evans and Willox 1991). The stocking of hatchery fish to mitigate stock declines, caused primarily by other factors such as habitat degradation and dam construction, can also accelerate the loss of wild stocks (Nehlsen et al. 1991), while failing to address the pri- mary causes of population decline. The overall effect is a loss of genetic diversity. The reliance on technological solutions such as the stocking of hatchery fish to redress man-made problems has been at the expense of ethical, ecological, and genetic considerations (Scarnecchia 1988; Hilborn 1992; Meffe 1992). Meffe (1992) has called this "techno-arrogance," an attitude that has clearly undermined conservation efforts. Artificial fisheries, which rely wholly on stocking for their continued existence, are not sustain- able and thus have no part in a conservation ethic. Even while the inadequacies of fisheries management strategies based on hatcheries and stocking are becoming evident, investments in intensive aquaculture are growing rapidly. Aquaculture is not based on conservation principles and, when practiced in natural systems, it may enhance