Temporal and spatial variability of allozyme and mitochondrial DNA markers among samples of naturally produced lake trout (Salvelinus namaycush) fry collected from Lake Ontario

The reproductive success of lake trout strains stocked into Lake Ontario was evaluated through examination of temporal and spatial variability of allozyme and mitochondrial DNA (mtDNA) markers. First, mtDNA variation was examined among the primary strains of lake trout stocked into Lake Ontario (Clearwater, Jenny, Killala, Manitou, Seneca, and Superior) using the restriction enzymes AvaI, BamHI, HinfI, and TaqI. Significant differences among the six strains indicated that mtDNA haplotype information could be used in addition to allozymes as baseline data for mixed stock analysis (MSA) of samples of lake trout fry collected from Lake Ontario. Second, the temporal stability of allozyme and mtDNA data was evaluated among three year classes (1988, 1989, and 1990) of lake trout propagated from gametes obtained from adults captured in Seneca Lake, New York. Cluster analysis of genetic distances of allozyme data grouped all Seneca Lake samples together and revealed a much lower level of differentiation than observed among the other strains stocked into Lake Ontario. Frequencies of mtDNA haplotypes were not significantly different among the 1988, 1989, and 1990 year class samples. MSA estimates of strain contribution to a mixture of wild fry from Lake Ontario were similar, regardless of which year-class sample from the Seneca Strain was used to create the baseline data. Thus, these samples were pooled to provide the Seneca strain baseline data for MSA of mixture samples of fry from Lake Ontario. Third, reproductive success of different hatchery strains was compared among four year-classes of naturally produced lake trout fry collected at Stony Island reef, three year classes of naturally deposited eggs from Stony Island, and a single year-class of naturally deposited eggs collected from Yorkshire Island reef (21 km west of the Stony Island site), Lake Ontario. MSA revealed a predominance (68 to 80%) of reproduction by the Seneca strain in all Stony Island samples. In contrast to the results at Stony Island reef, the Seneca strain contributed less than 12% of the gametes to the Yorkshire Island sample, with the balance of progeny due to reproduction by Killala, Manitou, and Superior strains (35, 28, and 23% respectively). The reproductive success of the Seneca strain over several years at the Stony Island site indicates the high suitability of this strain for the rehabilitation program at some locations in Lake Ontario. However, reproductive contributions made by Killala, Manitou, and Superior strains to naturally deposited eggs collected from Yorkshire Island suggests that other strains also have potential for fry production in Lake Ontario. Thus, management decisions should not be made that would eliminate stocking of other strains based on the apparent success of the Seneca strain at a single reef location.