Effectiveness of the Gull Island Refuge for Lake Trout in Lake Superior

Johnson, Melissa

The Gull Island refuge was created in 1976 in response to overfishing of the lake trout population in the Apostle Islands. My objective was to determine if lake trout abundance, growth, maturity, and mortality differed inside and outside the refuge, before and after the refuge was created. To address my objective, I compared abundance, growth, maturity, and mortality between lake trout captured inside and outside the refuge during spring large-mesh and summer graded-mesh gill-net surveys. Wild adult lake trout abundance increased significantly, while stocked adult lake trout abundance decreased significantly after the refuge was created. Wild adult and juvenile lake trout were significantly more abundant inside than outside the refuge, and stocked adult lake trout were less abundant inside than outside the refuge. Lake trout grew faster to a shorter asymptotic length inside the refuge than outside the refuge. Lake trout matured at an older age inside the refuge than outside the refuge. Lake trout suffered significantly lower mortality inside the refuge than outside the refuge. I conclude that the Gull Island refuge enhanced wild lake trout population growth in the Apostle Islands region and should be retained in the future to sustain conditions that favor population growth.