Origins of hatchery-reared lake trout Salvelinus namaycush to Lake Michigan’s sport fishery reflect trends in regional relative survival

Abstract

Fisheries management depends on understanding fish movements, especially in large systems. In Lake Michigan, lake trout are stocked for rehabilitation and to support a diverse, multi-million dollar sport fishery. We described the contributions of lake trout stocked at offshore and onshore locations to Lake Michigan’s sport fishery at multiple spatial scales. We also assessed lake trout relative survival and age-related seasonal movements. Offshore reefs, which historically were important sources of lake trout recruitment and are currently fishery refuges, served as source-populations for nearshore fisheries, as offshore-stocked lake trout comprised 58% of recoveries lakewide and were predominant in fisheries from 9 of 13 management units. By contrast, lake trout stocked onshore primarily had local importance, consistent with the management aim to directly benefit nearshore fisheries. Lake trout relative survival significantly differed among stocking regions but not between the two genetic strains compared. Lake trout stocked at two of the three offshore regions, Julian’s Reef and Southern Refuge, had higher relative survival (0.022–0.038 fish/sampling day/100,000 fish stocked) compared to the three onshore stocking regions (0.001–0.013) and the offshore Northern Refuge (0.011), which helps explain the predominance of offshore-stocked fish in fisheries at most locations. In addition, offshore-stocked fish were most available to sport fisheries in multiple regions during summer, while mature fish generally returned to their stocking region in fall, presumably to spawn. This study demonstrated that stocking at offshore locations in Lake Michigan supported both lake trout rehabilitation efforts and sport fisheries, and illustrates how spatial ecology can help inform fisheries management.