Spawning by Stocked Lake Trout on Shallow, Near-Shore Reefs in Southwestern Lake Michigan

Abstract

Restoration of self-sustaining populations of lake trout in the Great Lakes has been a goal of state, provincial, and federal agencies for over three decades. Juvenile lake trout have been stocked into Lake Michigan since 1965, but to date there has been limited evidence of spawning by adult feral fish on natural reefs. Although the restoration effort has focused on historically-used offshore spawning reefs in the last decade, the only study of spawning on a deep reef in Lake Michigan failed to find any evidence of egg deposition. Working on the hypothesis that stocked lake trout may be spawning on shallow reefs, the nearshore area of southwestern Lake Michigan was surveyed to locate areas of cobble substrate. The few areas of cobble substrate which were found appeared to provide marginal habitat for overwinter egg incubation, due to the lack of interstitial depth. Egg nets and traps were set on several reefs in the fall; eggs were recovered from four of six sites in 1991 and from three of four sites in 1992. The highest numbers of eggs 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 shore. Despite the recent focus of stocking and management efforts on deep, 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 in southern Lake Michigan.