Movements of Lake Trout in U.S. Waters of Lake Superior During 1973-2001

Abstract

Fisheries managers presently manage lake trout Salvelinus namaycush populations in Lake Superior using models for management areas that assume lake trout do not move between management units. Mean distance traveled by lake trout tagged in Lake Superior has been shown to vary from 9 miles to 67 miles, but effects of length, gender, origin (wild-born or hatchery-reared), age, and time at liberty on distance moved have not been determined for lake trout in Lake Superior. Therefore, I: quantified movement rates of lake trout between management units in U.S. waters of Lake Superior, calculated the mean distance traveled by lake trout, and determined whether length, gender, origin, age, and time at liberty influenced the distance moved by lake trout tagged in six different U.S. management units of Lake Superior. Of 46,407 lake trout tagged at 195 sites in Lake Superior during spring, summer, and fall, 1973-2000, 2,763 were recaptured in assessment, angling, and commercial fisheries. One thousand eight hundred and four recaptures were standardized by recapture effort for movement rate analyses. Most lake trout remained in the management unit in which they were tagged for all tagged populations, and emigration to other management units generally decreased with distance from the management unit where the lake trout were tagged. Lake trout tagged in WI-1 and MI-3 emigrated at equal rates to the east and west, while lake trout tagged in WI-2 and MI-5 emigrated at greater rates to the west than east, and lake trout tagged in MI-2 and MI-4 emigrated at greater rates to the east than west. On average, lake trout traveled 32.70 miles while at large. The average distance moved by lake trout tagged in six different management units differed significantly among management units. Distance moved did not differ significantly with length, age, time at liberty, gender, or origin for five of six tagged populations. Distance moved varied significantly with time at liberty for lake trout tagged in MI-5. Fishery managers can use my results to: (1) account for emigration and immigration of lake trout between management units in Lake Superior in statistical catch-at-age models, (2) determine that 90% of lake trout spawning less than 91.76 miles (147.67 km) from a jurisdictional boundary are moving across that jurisdictional boundary between spawning events, (3) determine that lake trout stocks that spawn on reefs less than 91.76 miles (147.67 km) apart from each other are mixing between spawning events, (4) assume that movements of lake trout tagged in WI-I, WI-2, MI-2, MI-3, and MI-4 are undirected, and (5) predict movement distances of lake trout tagged in MI-5 based on time at liberty.