Lake Trout Rehabilitation in the Great Lakes: an Evolutionary, Ecological, and Ethical Perspective

Abstract

We reviewed key features of the evolutionary biology of lake trout (Salvelinus namaycush) and their significance for rehabilitation programs in the Great Lakes. Despite repeated transloca-tion by glacial advances during the Ice Age (the Pleistocene) that eliminated most populations, lake trout have genetic diversity comparable with other North American salmonines. Various embryological and adult features suggest lake trout had a long reproductive history in lakes, although river spawning may be a primitive feature of the species and may have been important in glacial refugia. Observations that hatchery-reared lake trout select mostly mainland shoals for spawning in the Great Lakes are interpreted by us to be a result of evolution in smaller lakes where the main source of spawning gravels is shoreline erosion. We hypothesize that longevity in lake trout (a record among chars) may have evolved because of a near absence of predation on adults in contrast to predation on juveniles that survived less well, in part, because of cannibalism. Longevity, a physiological ability to colonize the coldest of waters during deglaciation, and an ecological role as a dominant piscivore in unperturbed systems all indicate that lake trout should fare best under conditions of low adult mortality and high biomass. Although the Great Lakes fish community is enriched compared with when lake trout populations were abundant or with where lake trout evolved, the species has the potential to suppress other fishes to its benefit. We provide ecological and ethical reasons why lake trout rehabilitation should be a priority for the Great Lakes: lake trout are particularly suited for the deepwater food chain, they are the only salmonine (among those currently stocked in the lakes) that have the potential to become self-sustaining at their current levels of abundance, and emphasis on stocked exotics reflects adherence to a scientifically obsolete philosophy of “wise use” that ignores evolutionary-ecological relationships. For fishery management, we recommend greater use of genetic diversity and of life stages capable of being imprinted, maintenance of high adult survivorship and biomass, and expanded communication with a wider array of clients. We also advocate lines of research that will test our management recommendations, including assessing the implications of attempting to keep the Great Lakes fish community in an early stage of succession.