An Ecosystem Perspective on Re-establishing Native Deepwater Fishes in the Laurentian Great Lakes

—Herein we examine scientific questions related to successful re-establishment of native deepwater fish communities in the Laurentian Great Lakes, and we (1) propose a conceptual model for native deepwater fish communities; (2) review current research and identify research hypotheses for lake trout Salvelinus namaycush, pelagic ciscoes Coregonus spp., and sculpins (Cottus spp. and Myoxocephalus spp.); (3) pose research questions emerging at community and ecosystem levels; and (4) identify high-priority research topics related to population re-establishment. The conceptual model is based on a generalized life cycle nested within processes at the population, metapopulation, community, and ecosystem levels. The conceptual model assumes that variation in population abundance is a natural phenomenon and that biodiversity contributes to ecosystem stability. Key research topics related to lake trout re-establishment include understanding recruitment variation over space and time, identifying sources of early life history mortality, determining the level of genetic differentiation among morphotypes and populations, and comparing the life history and ecology of lean lake trout with those of other lake trout morphotypes. Key research topics related to re-establishing deepwater species of cisco include resolving uncertainties in species identifications, understanding processes maintaining distinctiveness among species, understanding processes leading to cyclic and erratic recruitment, and developing effective propagation methods. Key research topics related to re-establishment of sculpin species include comparing spawning ecology and early life history of each species, determining population structure, and evaluating the feasibility of live-transfer methods. Key research topics related to communityand ecosystem-level interactions include understanding large-scale directional influences on community function, expanding current views on ecological succession in large lakes, and determining the evolutionary role of diel vertical migration in phenotypic diversification of deepwater fishes. Finally, we propose that research in four topical areas are most pertinent to re-establishing native deepwater fishes: life history bottlenecks, population and metapopulation dynamics, matching fish phenotypes to stocking sites, and propagation and stocking methods. Entire communities of deepwater fishes were eliminated from nearly all five Laurentian Great Lakes by the mid-20th century. With few exceptions, deepwater fishes have remained absent from large volumes of deepwater habitat to the present day (Eshenroder and Burnham-Curtis 1999). The Great Lakes Fishery Commission (GLFC), a binational agency coordinating the research and management of Great Lakes fisheries, has stressed the importance of conserving biological diversity represented in the form of populations, species, and communities (GLFC 2001). Deepwater communities composed of lake trout Salvelinus namaycush, burbot Lota lota, ciscoes Coregonus spp., whitefish Prosopium spp., and sculpins (Cottus spp. and Myoxocephalus spp.) were once major components of this diversity. Present conditions offer promise for future re-establishment of native deepwater fishes. For example, potential source populations exist in Lake Superior and elsewhere that could be used for reintroduction into lakes where species are extirpated. Many variables contributing to the initial decline (i.e., effects of predation by sea lampreys Petromyzon marinus; overharvest) are now managed cooperatively by state, federal, and tribal agencies. Furthermore, rainbow smelt Osmerus mordax and alewives Alosa pseudoharengus are presently lower in abundance than when they were believed to have contributed to native species decline (O’Gorman and Stewart 1999). This paper identifies key scientific questions related to successful re-establishment of native deepwater fish communities in the Laurentian Great Lakes. Reestablishment refers to reintroduction followed by long-term persistence of populations through natural reproduction. The term ‘‘re-establishment’’ does not mean that previous conditions are recovered (i.e., ‘‘restoration’’) but rather acknowledges that native Great Lakes communities have been irreversibly altered and that native fish recovery must proceed * Corresponding author: [email protected] 1 Present address: Washington Department of Fish and Wildlife, 600 Capitol Way North, Olympia, Washington 98501, USA. Received August 29, 2008; accepted December 29, 2008 Published online September 3, 2009 1352 North American Journal of Fisheries Management 29:1352–1371, 2009 Copyright by the American Fisheries Society 2009 DOI: 10.1577/M08-194.1 [Article]