The Mid-Lake Reef Complex (MLRC), a large area of deep (> 40 m) reefs, was a major site where indigenous lake trout (Salvelinus namaycush) in Lake Michigan aggregated during spawning. As part of an effort to restore Lake Michigan's lake trout, which were extirpated in the 1950s, yearling lake trout have been released over the MLRC since the mid-1980s and fall gill net censuses began to show large numbers of lake trout in spawning condition beginning about 1999. We report the first evidence of viable egg deposition and successful lake trout fry production at these deep reefs. Because the area's existing bathymetry and habitat were too poorly known for a priori selection of sampling sites, we used hydroacoustics to locate concentrations of large fish in the fall; fish were congregating around slopes and ridges. Subsequent observations via unmanned submersible confirmed the large, fish to be lake trout. Our technological objectives were driven by biological objectives of locating where lake trout spawn, where lake trout fry were produced, and what fishes ate lake trout eggs and fry. The unmanned submersibles were equipped with a suction sampler and electroshocker to sample eggs deposited on the reef, draw out and occasionally catch emergent fry and collect egg predators (slimy sculpin Cottus cognatus). We observed slimy sculpin to eat unusually high numbers of lake trout eggs. Our qualitative approaches are a first step toward quantitative assessments of the importance of lake trout spawning on the MLRC.
|Original language||English (US)|
|Number of pages||15|
|Journal||Journal of Great Lakes Research|
|State||Published - 2006|
Bibliographical noteFunding Information:
This work was funded by the University of Wisconsin Sea Grant Institute under grants from the National Sea Grant College Program, National Oceanic and Atmospheric Administration, U.S. Department of Commerce, and from the State of Wisconsin, Federal grant number NA16RG2257, project number R/LR-89. Mapping was funded by the United States Fish and Wildlife Service Restoration Program, NOAA EXPLORE Program, and the Great Lakes Fishery Trust. Additional grant support and ROV support were provided by the National Underseas Research Program. We thank the crews of the R/V Neeskay (University of Wisconsin-Milwaukee) and R/V Blue Heron (University of Minnesota-Duluth) for their exemplary hospitality. Dave Lovalvo owns and operates the Eastern Oceanics ROV and was very inventive. We also appreciate the help of numerous assistants and volunteers for braving the gales of November. In particular, we appreciate the dedication of Kirby Wolfe and Michelle Luebke, Carolina Penalva, and Steve Hensler. Chris Houghton and Tom Hanson helped draft figures. This paper is dedicated to the late Ross Horrall, who showed the deep reefs to Janssen in 1976.
- Great Lakes
- Salvelinus namaycush