Michigan Department of Natural Resources
Fisheries Research Report No.1871, 1979
Utilization of Traditional Spawning Reefs by Hatchery Lake Trout in the Upper Great Lakes
James W. Peck
Abstract.-Large-mesh gill nets, fished during the spawning seasons in 1973-76, demonstrated that lake trout abundance was sufficient for natural reproduction on 17 of 32 traditional spawning reefs in Lake Superior and 2 of 19 in Lake Michigan. Spawning lake trout also were abundant on six of eight reefs in Grand Traverse Bay, Lake Michigan, that were not traditional reefs. Hatchery fish that strayed from the planting sites comprised 84% of the spawners in Lake Superior and at least 99% in Lake Michigan. Spawning occurred on most reefs as evidenced by the presence of ripe to spent lake trout. On certain reefs, additional evidence of spawning was the occurrence of lake trout eggs in piscine predators and in the substrate.
Male and female spawner lake trout averaged 8 and 9 years old, respectively, in Lake Superior and about 2 years younger in Lake Michigan. Males outnumbered females on spawning reefs in both lakes by a ratio of about 3:1. Spawning lake trout in 1973-76 matured at a younger age and grew faster than natural spawning populations in Lake Superior in 1953, but spawning period and sex ratio were similar.
A list was made of the 123 traditional spawning reefs that were identified in the study.