the program's call for ecosystem management. Multispecies management is now being explored. Whether multispecies management and ecosystem management are only distant goals or are imminently achievable are questions that the CBP will face as it attempts to reconcile the demands of multiple users with conditions required to restore a diverse, productive, and sustainable ecosystem.
Great Lakes fisheries and the fish communities on which they are based have changed dramatically in the past 150 years. These large lakes contain one-fifth of the surface fresh water on the earth; their drainage basins are heavily developed and contain large portions of the human populations of the United States and Canada. Changes in fish communities have resulted from invasions and stocking of exotic species; overfishing; pollution; and loss or damage of habitat, especially in bays, tributaries, and shallower basins. The usefulness of fish as human food has been reduced by bioaccumulation of anthropogenic toxic substances; those chemicals have probably affected a variety of fish populations directly, especially salmonids (e.g., Mac and Gilbertson 1990, Mac et al. 1993). Yet important commercial (e.g., lake whitefish [Coregonus clupeaformis], Ebener 1997) and recreational fisheries persist or have recovered. Indeed, recreational fisheries have become very important in the Great Lakes, involving both introduced species such as Pacific salmon (Oncorhynchus spp.) and native species such as walleye (Stizostedion vitreum) (Knight 1997, Lichtkoppler 1997) and lake trout (Salvelinus namaycush) (Schreiner and Schram 1997). The management paradigm for the Great Lakes has been to take an ecosystem approach to rehabilitation of the ecological systems on which the fisheries depend (Francis et al. 1979). Even though the problems have been catastrophic at times, such as the elimination or near-elimination of fish species (Kerr and Ryder 1997), there is some positive sentiment among fishery managers, because of some successes in reversing or coping with a number of serious problems and because of the important recreational fisheries.
Sea lamprey (Petromyzon marinus), alewife (Alosa pseudoharengus), and rainbow smelt (Osmerus mordax) have invaded the Great Lakes in the past, severely affecting the native pelagic fish species. A combination of biocides to kill larval sea lamprey, fisheries for alewife and rainbow smelt, and artificial propagation of lake trout and Pacific salmon have been used to rehabilitate native populations and provide sport fisheries. Problems continue in terms of fish health (disease) and stocking at levels that overexploit the prey base, and the assemblage of fish species in the Great Lakes today is enormously different from the preindustrial assemblage. In particular, species of Pacific salmon, sea lamprey, and rainbow smelt are common, and some species have been exterminated (Becker 1983, Kerr and Ryder 1997).
Sources of input to the lakes of toxic and carcinogenic compounds have been