The Effectiveness of the Lake Trout Refuges in Lake Superior

Gull Island Shoal (GIS) refuge was created in 1976 in response to the lake trout population collapse in the Apostle Islands region of Lake Superior.  My objective was to determine if lake trout abundance, growth, maturity, and mortality differed inside and outside refuge boundaries, before and after GIS was created.  In GIS, wild adult lake trout abundance increased significantly whereas stocked adult lake trout abundance decreased significantly after the refuge was created.  Wild adult lake trout were more abundant inside GIS than outside and stocked adult lake trout were less abundant inside than outside after the refuge was created.  In GIS, wild juvenile lake trout abundance was significantly greater inside than outside, whereas stocked juvenile lake trout abundance did not differ significantly inside and outside.  Lake trout outside grew at an instantaneous rate of 0.098/year to an asymptotic length of 35.8 inches, whereas lake trout inside grew at a faster instantaneous rate (0.144/year) to a shorter asymptotic length (33.4 inches).  Lake trout inside were younger than outside the refuge.  Lake trout sampled inside GIS refuge suffered significantly lower mortality than lake trout sampled outside.  The GIS refuge is enhancing wild lake trout population growth in the Apostle Islands region.