Recruitment Dynamics of the 1971–1991 Year-Classes of Lake Trout in Michigan Waters of Lake Superior

Abstract

In the 1950s, populations of lake trout Salvelinus namaycush in Lake Superior collapsed because of excessive exploitation and predation by sea lampreys Petromyzon marinus. Restoration began in the 1950s with the stocking of juvenile, hatchery-reared lake trout and controls on fisheries and sea lampreys. Partial restoration was declared in 1996 because wild fish made up most of the populations in many areas, especially in Michigan waters, so stocking was dramatically curtailed in most areas. We evaluated the production of age-7 lake trout (recruits) by age-8 and older wild and stocked parental lake trout (spawners). Using Ricker stock–recruitment models, we also evaluated the effects of large-mesh (114-mm stretch measure) gill-net effort on wild lake trout recruitment in Michigan waters of Lake Superior during 1970–1998. In general, the density of wild lake trout spawners increased, whereas that of stocked lake trout spawners decreased in all management areas investigated. The density of recruits was best described by the combined density of wild and stocked parents, which suggested similar reproductive contributions for both. Recruitment rates declined significantly with increasing spawner density in four of the five management areas and suggested that carrying capacities were reached and exceeded, which may serve as an indicator of population restoration. We conclude that both wild and stocked lake trout have contributed to the recruitment of lake trout in Michigan waters of Lake Superior. Large-mesh gill-net fishing effort varied in all Michigan management areas but did not account for the significant variation in wild lake trout recruitment. We conclude that levels of large-mesh gill-net fishing effort during 1970–1998 were not having an appreciable effect on wild lake trout recruitment in Michigan waters of Lake Superior.