SPAWNING BY STOCKED LAKE TROUT ON SHALLOW, NEAR-SHORE REEFS IN SOUTHWESTERN LAKE-MICHIGAN

Restoration of self-sustaining populations of lake trout in the Great Lakes has been a goal of state, provincial, and federal agencies for o ver three decades. Juvenile lake trout have been stocked into Lake Mic higan since 1965, but to date there has been limited evidence of spawn ing by adult feral fish on natural reefs. Although the restoration eff ort has focused on historically-used offshore spawning reefs in the la st decade, the only study of spawning on a deep reef in Lake Michigan failed to find any evidence of egg deposition. Working on the hypothes is that stocked lake trout may be spawning on shallow reefs, the nears hore area of southwestern Lake Michigan was surveyed to locate areas o f cobble substrate. The few areas of cobble substrate which were found appeared to provide marginal habitat for overwinter egg incubation, d ue to the lack of interstitial depth. Egg nets and traps were set on s everal reefs in the fall; eggs were recovered from four of six sites i n 1991 and from three of four sites in 1992. The highest numbers of eg gs were collected on a breakwall in Indiana (1 egg/net/day). All sites where eggs were found were less than 12 m deep and within 4 km of sho re. Despite the recent focus of stocking and management efforts on dee p, offshore reefs in Lake Michigan, lake trout spawn in shallow water. Imprinting to spawning sites does not explain this behavior. Spawning on the breakwall suggests that there is a paucity of good substrate i n southern Lake Michigan.