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

Differentiation of deep-water lake charr Salvelinus namaycush in North American lakes

“…Of the lakes known to harbor deep-water lake trout, only Lake Superior was divided during deglaciation into separate sub-basins (glacial Lakes Duluth and Minong) (Hough 1963). Eshenroder et al (1995) proposed a variant of Hypothesis 2 especially relevant to differentiation of deep-water lake charr in the Great Lakes. Under their concept, shallow-water spawning sites at low-water stages become deepwater sites as lake levels returned to modern elevations.…”

“…Although one of the six named species (Todd and Smith 1992), C. zenithicus, may predate the proglacial lakes (Turgeon et al 1999), all of the species had traits, such as high lipid levels or long paired fins (Koelz 1929;Krause et al 2002), of vertically migrating deep-water planktivores. If Eshenroder and Burnham-Curtis (1999) were correct in surmising that M. relicta, a vertically migrating, lipid-rich food of deepwater ciscoes (Koelz 1929), was important in their evolution, then functional deepwater ciscoes, unlike M. relicta, are postglacial in origin. I use ''functional'' to account for the possibility that C. zenithicus colonized the proglacial lakes along with C. artedi (its sister species) and M. relicta.…”

The significance of man-made structures for lake trout spawning in the Great Lakes: are they a viable alternative to natural reefs?

“…Kelso et al (1995) reported shoreline spawning by mixed stocks of wild and stocked lake trout in depths of < 5 m along the north shore of Lake Superior indicating that this behaviour may be an innate characteristic of the species. Eshenroder et al (1995) suggested that shallow water spawning by lake trout was the result of evolution in small inland lakes where the main source of spawning substrate was shoreline erosion.…”

Contribution of lake trout stocked as fry to an adult population in Lake Superior

“…Lake trout are the native top predator in Lake Superior, and they are particularly suited to the cold deepwater food chain (Eshenroder et al, 1995b), but populations suffered severe declines in the 1950s due to an intense fishery and sea lamprey Petromyzon marinus predation (Hansen et al, 1995). The Great Lakes Fishery Commission (GLFC) has promoted reestablishment of lake trout in all the Laurentian Great Lakes (GLFC, 2001), and efforts to reestablish lake trout by stocking yearlings (marked with a fin clip) into the Great Lakes have met with varying success.…”

“…Lake trout stocked as yearlings, regardless of stocking location, tend to spawn in shallow water along shorelines where wave action, ice scour, and siltation limit egg survival (Eshenroder et al, 1995a;Krueger et al, 1986;Peck, 1979). Stocking of eggs or sac fry directly onto historical spawning reefs where natural reproduction is low or absent, in the season when that life stage would normally be found in the wild, has been recommended to promote imprinting and survival of lake trout and their progeny (Eshenroder et al, 1995b(Eshenroder et al, , 1999Horrall, 1981;Marsden et al, 1995). Citing these reasons, recent lake trout rehabilitation plans for most of the Great Lakes include the stocking of early life history stages to reduce time to rehabilitation (Bronte et al, 2008;Ebener, 1998;Hansen, 1996;Markham et al, 2008), though evidence of successful fry stocking has been lacking.…”