Dynamics of Lake Trout Recruitment in Michigan Waters of Lake Superior

Abstract

Lake Superior has been the site of an extensive restoration plan focusing on the lake trout (Salvelinus namaycush). Historically, the lake trout was a dominant top predator in the lake and during 1913-50 supported a commercial fishery with an average annual harvest of 2-million kg. In the 1950s, the lake trout population crashed due to overfishing and sea lamprey (Petromyzon marinus) predation. The restoration process · began in the 1950s with the stocking of juvenile, hatchery-reared lake trout and controls on sea lampreys and fisheries. In March 1996, after 3 5 years of effort, fishery managers declared victory in their pursuit of lake trout restoration and decided to cease stocking. The objectives were to quantify the contribution of wild and stocked lake trout to contemporary recruitment of wild lake trout and to quantify the effects of large-mesh (114-mm stretch measure) gill net effort on wild lake trout recruitment in Michigan waters of Lake Superior. For the first objective, Ricker stock-recruitment models were used to quantify the contribution of wild and stocked lake trout to recruitment of wild fish. Density of wild lake trout generally increased, whereas density of stocked lake trout generally decreased in all Michigan management units of Lake Superior during 1970-1998. The density of wild and stocked parents best described recruitment of wild lake trout during 1970-1990, but stocked parents were only 52.2% as effective as wild parents. Recruitment rates of wild and stocked parents declined significantly with density in all Michigan management units. Peak recruitment was similar for wild and stocked fish, but the stocked fish parental density needed to reach peak recruitment was twice as high for stocked parents as for wild parents. I conclude that both wild and stocked fish have contributed to recruitment of lake trout in Michigan waters of Lake Superior, but that wild fish were twice as reproductively effective as stocked fish. For the second objective, I used a Ricker stock-recruitment model to quantify the effect of large-mesh (114-mm stretch measure) gill net effort on lake trout recruitment. Large-mesh gill net fishing effort varied differently in all Michigan management units, but did not account for significant variation in wild lake trout recruitment. I conclude 'that current levels of large-mesh gill net fishing effort are consistent with lake trout restoration goals in Michigan waters of Lake Superior.