Population Dynamics of F1 Splake (Salvelinus fontinalis × S. namaycush) in Lake Huron

Ninety-eight percent of 5391 F1 splake recovered from a 1966 planting of 49,000 yearlings in Burnt Island Bay (45°50′N, 82°57′W) on the south shore of Manitoulin Island were taken within 32 km (20 miles) of the planting site. Remaining recaptures were made at distances up to 322 km (200 miles).Growth rates of the hybrids in Lake Huron exceeded those reported for native and planted lake trout. A commercial size of 0.9 kg (2 lb) round weight was attained by the fall of their 2nd year in the lake. The splake grew rapidly through the winter months. Yearlings fed mainly on invertebrates and 2- to 4-year-olds fed almost entirely on fish.Eight percent of 3054 hybrids examined had one or more lamprey marks. Fish less than 30 cm (12 inches) bore no evidence of lamprey attack; larger hybrids showed frequencies of lamprey marks increasing from 5.4% for 30- to 40-cm fish to 11.6% for those larger than 40 cm. The incidence of fresh lamprey marks was minimal in spring and early summer and reached a peak in September when more than 20% of the specimens bore fresh marks.Of the 2- and 3-year-old splake recovered, 50 and 40%, respectively, were males. The onset of sexual maturity in both sexes occurred at age II. By age III, 86% of the males and 58% of the females were mature. Ripe 3-year-old hybrids of both sexes were captured over former lake trout spawning grounds. Fecundity of 3-year-old females averaged 2512 eggs. Although survival to age IV was low, a substantial number of the hybrids attained sexual maturity.A total of 8.4% of the planting of 49,000 yearling hybrids was reported taken by sport and commercial fisheries during a 3-year period.