Genetic profiles of selected brook trout Salvelinus fontinalis populations from Lake Superior, Lake Huron and selected hatcheries

Burnham- Curtis, Mary

In the Lake Superior drainage basin, brook trout are the only extant indigenous stream salmonid since the loss of several populations of river-run lake trout in the last century. Recent field investigations have shown evidence that brook trout populations in some Lake Superior tributaries are self-sustaining, and in some populations significant genetic diversity is still present. Some Lake Superior tributaries contained populations of “coaster” brook trout, a form of brook trout which spends a majority of its adult life in the open water of Lake Superior and returns to shoreline reefs or some upstream sites to spawn. Populations of coasters throughout the Lake Superior basin have suffered severe declines, and only a few streams are thought to still harbor remnant stocks. From throughout the Lake Superior basin, brook trout populations were sampled that represented suspected remnant wild populations, historical “coaster” populations, and populations with counterparts in above-barrier sections of streams. Much of the genetic diversity present among Lake Superior brook trout is partitioned among individual populations. Populations of brook trout in the Lake Superior basin show levels of genetic variability in the mitochondrial DNA genome that suggest that some populations are still sustained by wild fish. The combined effects of population declines and hatchery supplementation are reflected in the mtDNA profiles of several populations in this survey for which only the most common mtDNA haplotype was detected. No unique genetic markers were found in the mitochondrial DNA to correlate with samples identified as coasters, but sample sizes of known coasters were small. Further work with more known coasters and nuclear markers such as microsatellite DNA loci may shed more light on how the coaster phenotype is produced.