Genetic Assessment of Strain-Specific Sources of Lake Trout Recruitment in the Great Lakes

Abstract

Populations of wild lake trout Salvelinus namaycush have been extirpated from nearly all their historical habitats across the Great Lakes. Efforts to restore self-sustaining lake trout populations in U.S. waters have emphasized the stocking of coded-wire-tagged juveniles from six hatchery strains (Seneca Lake, Lewis Lake, Green Lake, Apostle Islands, Isle Royale, and Marquette) into vacant habitats. Strain-specific stocking success has historically been based on estimates of the survival and catch rates of coded-wire-tagged adults returning to spawning sites. However, traditional marking methods and estimates of relative strain abundance provide no means of assessing strain fitness (i.e., the realized contributions to natural recruitment) except by assuming that young-of-the-year production is proportional to adult spawner abundance. We used microsatellite genetic data collected from six hatchery strains with likelihood-based individual assignment tests (IA) and mixed-stock analysis (MSA) to identify the strain composition of young of the year recruited each year. We show that strain classifications based on IA and MSA were concordant and that the accuracy of both methods varied based on strain composition. Analyses of young-of-the-year lake trout samples from Little Traverse Bay (Lake Michigan) and Six Fathom Bank (Lake Huron) revealed that strain contributions differed significantly from estimates of the strain composition of adults returning to spawning reefs. The Seneca Lake strain contributed the majority of juveniles produced on Six Fathom Bank and more young of the year than expected within Little Traverse Bay. Microsatellite markers provided a method for accurately classifying the lake trout hatchery strains used for restoration efforts in the Great Lakes and for assessment of strain-specific reproductive success.

Effects of coancestry on accuracy of individual assignments to population of origin: examples using Great Lakes lake trout (Salvelinus namaycush)

“…The SMD and Isle Royale (SIW) strains were selected as the low F st case (F st [ 0.01). Details on hatchery strains may be found in Page et al (2003). Spawning of adults were conducted by U.S.…”

“…We then summarized results characterizing the importance of gene correlations and apportionment of genetic variation on assignment error rate. We estimated accuracy of individual strain classification using multilocus genotype frequencies of each lake trout broodstock as described previously (Page, 2001;Page et al, 2003) using the leave-one-out procedure (Efron, 1983). We assigned progeny from low coancestry and high coancestry groups of unknowns for each inter-strain comparison to determine whether accuracy of individual assignments was random across samples.…”

Heritage strain and diet of wild young of year and yearling lake trout in the main basin of Lake Huron

“…A previous genetic study of lake trout from Lake Huron showed that these three strains accounted for the majority of wild lake trout captured (Page et al 2003). In addition, these strains accounted for the majority (N80%) of the stocking in the areas were sampled and tagging data indicated that most lake trout stocked into northern Lake Huron remained in that area (Madenjian et al 2004).…”

“…Since their introduction into Lake Huron, Senecastrain lake trout made up the majority of spawners found in the Drummond Island Refuge and on Six Fathom Bank between 1991 and 1995 even though equal numbers of each strain were stocked (Table 1). In the Drummond Island Refuge, Seneca-strain lake trout made up nearly 100% of spawning sized lake trout captured between 1991 and 1995; on Six Fathom Bank, over half of the spawning-sized lake trout captured were of the Seneca strain (Page et al 2003).…”

“…Numerous genetic and tagging studies on lake trout strain performance in Lake Ontario (Marsden et al 1989, Grewe et al 1994, Lake Michigan (McKee et al 2004), and Lake Huron (Page et al 2003, Stott et al 2004 suggest that the Seneca Lake strain has been most successful in the Great Lakes. Although stocked fish support substantive recreational, commercial, and subsistence fisheries, the goal of self-sustaining lake trout populations remained elusive, primarily because of chronic recruitment failure of naturally reproduced fish as evidenced by predominance (N96%) of marked hatchery fish in agency surveys.…”