Lake Trout Movements in Northwestern Lake Michigan

Abstract

We quantified the distance that lake trout Salvelinus namaycush moved in northwestern Lake Michigan and examined (1) the directional preference and (2) the effect of population density on movement. Lake trout were captured in spring and fall 1983–1996, tagged with Floy anchor tags, and recaptured during subsequent agency sampling and by commercial fishers and anglers during 1983–1997. Angler recaptures were used to quantify movements; these recaptures were standardized to 10,000 salmonid angler-hours (giving recaptures per effort (RPE)) to account for the spatial and temporal variation in recapture effort. Movement was inferred from the spatial and temporal differences in the distribution of RPE. The dispersal radius, an index of the area occupied by tagged lake trout, was defined as the area containing 90% of the total RPE. It was estimated by fitting the cumulative proportion of RPE versus distance from the tagging location to an exponential sigmoid model and using inverse prediction. We used linear regression to test for density dependence in movement. Lake trout tagged in spring occupied a larger area than those tagged in fall and increased their range as population density increased. Directional movement differed for spring- and fall-tagged fish. Spring-tagged fish showed no directional tendencies in movement, but fall-tagged fish tended to move more to the south than to the north. There was no significant difference in directional movement between recapture seasons. Our results will be useful for the management and restoration of lake trout in Lake Michigan by providing information that can be incorporated into population models and management decisions about refuges and management zones within the lake.