Lake Trout in the Great Lakes: History, Molecular Genetics, Physiology, Strain Comparisons, and Restoration Management

This paper reviews historical differences among native lake trout (Salvelinus namaycush) populations, genetic comparisons of populations, heritability of physiological traits, performance of strains after stocking, and the role of genetics in management. Differences among lake trout were historically recognized by aborignal people, Jesuit missionaries, and French voyageurs, and later by naturalists and biologists. Lean trout represented trout that typically spawned on shallow rocky shoals. Exceptions included river spawning populations in Lake Superior and stocks reported to spawn over beds of algae in Lakes Superior and Michigan. Sisco wets had high fat content, were caught in deep water, and likely spawned year-round. Humpers resembled the siscowet but had thin ventral body walls, intermediate fat content, and small size at maturity. The siscowet form and different stocks of lean trout were reported from all the Great Lakes except Lake Ontario. Data from chromosomal banding, allozyme data, and mitochondrial DNA analysis confirmed that genetic differences occur among the three forms. Genetic data also provided evidence for distinctive populations within forms. Fat content, swimbladder gas retention, and developmental rates of eggs were different among some populations and appear to be heritable. Differences among strains after stocking have occurred in survival, dispersal from stocking location, depth distribution, and reproduction. Genetic considerations have been incorporated in species restoration plans but full use has not been made of available genetic information about lake trout. Reproductive performance of different strains should be a central focus in the evaluation of stocking programs. In Lake Superior, high priority should be given to the conservation of native stocks, the last remaining gene pools of Great Lakes lake trout. Goals for management should embrace a vision that restoration is accomplished only when some level of diversity has been re-established. Achievement of restoration should require the existence of naturally-reproducing, self-sustaining populations of different lake trout forms that use a variety of habitats. INDEX WORDS: Siscowet, reproduction, stocking, mitochondrial DNA, genetics, lake trout, Great Lakes.