HATCHERY ORIGINS OF NATURALLY PRODUCED LAKE TROUT FRY CAPTURED IN LAKE-ONTARIO - TEMPORAL AND SPATIAL VARIABILITY BASED ON ALLOZYME AND MITOCHONDRIAL-DNA DATA

Stocking of juvenile lake trout reared in hatcheries has been one of s everal management actions used to restore self-sustaining populations of lake trout Salvelinus namaycush in the Great Lakes. Since 1973, Lak e Ontario has been stocked predominately with Clearwater, Jenny, Killa la, Manitou, Seneca, and Superior strains. Reproductive success of the se strains was assessed by using allozyme and mitochondrial DNA (mtDNA ) characters with mixed-stock analysis. Parental origins of wild fry w ere compared over several years at Stony Island reef and between Stony Island reef and Yorkshire Island reef in 1990. Strain origins at Ston y Island reef were examined among four year-classes (1986, 1988, 1989, and 1990) of wild fry and among three year-classes (1988, 1989, 1990) of fry reared from eggs collected in late autumn. Allelic frequencies were not different among year-classes within the wild fry and egg col lections from Stony Island reef (P 0.05). Frequencies of mtDNA haploty pes also were not different among the 1988, 1989, and 1990 fry samples (mtDNA data were unavailable for the 1986 sample). Allozyme compariso ns between fry and egg samples over the three year-classes indicated t hat embryos collected in autumn were genetically similar to fry the ne xt spring. Based on mixed-stock analysis, 67-90% of parental contribut ions were from the Seneca strain; the remaining contribution was attri buted to Killala and Superior strains. At the Yorkshire Island site, o nly eggs were sampled and analyzed (no fry). In contrast to Stony Isla nd, strain contributions to this sample were 35% Killala, 28% Manitou, and 23% Superior. Hatchery strains identified at the Yorkshire Island site fertilized and deposited eggs but do not appear to produce fry ( only two fry were collected over a 3-year period). Thus, the suitabili ty of strains other than Seneca in producing wild fry remains in quest ion. The consistent reproductive success of the Seneca strain over 5 y ears at Stony Island reef relative to their low level of stocking indi cates the suitability of this strain for restoration of lake trout pop ulations at shallow-water reef locations in Lake Ontario.