Reef Utilization By Lake Trout and Progress Toward Rehabilitation in Southern Lake Michigan

Before their collapse in the 1950s, Lake Trout was the top predator in Lake Michigan. Since 1965 a variety of stocking strategies have been implemented to facilitate reestablishment.  All Lake Trout stocked in Lake Michigan have been marked with fin clips or adipose fin clip and coded-wire tag (CWT); Julian’s Reef, a designated Lake Trout stocking area in Illinois waters, has been stocked since 1981. To evaluate rehabilitation success we monitored the spawning population at Julian’s Reef with annual (1999-2014) October-November gill net surveys and compared this to the success of a nearby undesignated location, Waukegan Reef. There was no difference in catch per unit effort between the spawning sites (P = 0.18). Unmarked fish have increased exponentially at both locations with 50% of the recent catch having no fin clips. Information from CWTs indicated that a greater proportion of fish sampled on both reefs were stocked outside of southern Lake Michigan (90-680 km away), and these fish were significantly older (P’s<0.01) compared to those stocked on Julian’s reef. Trends in age, origin, and abundance offer valuable insight into the populations utilizing designated and undesignated reefs, and should be considered in a lake wide monitoring context by Lake Michigan managers.