Benthic Habitats and the Effects of Fishing

Using Laser Technology to Characterize Substrate Morphology and Geology of Selected Lake Trout Spawning Habitat in Northern Lake Michigan

Peter W. Barnes, Guy W. Fleischer, James V. Gardner, and Kristen M. Lee

doi: https://doi.org/10.47886/9781888569605.ch15

Abstract. As part of a strategy to reestablish native stocks of lake trout Salvelinus namaycush, six areas of offshore and coastal Lake Michigan benthic habitat were mapped with a bathymetric laser system. This allowed us to visualize and map morphologic detail by at least an order of magnitude over existing data. Decimeter elevation–bathymetric data, referenced to the International Great Lakes datum of 1985, were obtained on a 4-m grid over a total area of about 200 km2 in water depths from 0 to 30 m. Based on the laser-derived morphology, regional geology and sparse samples, three geologic regimes were used for substrate–habitat classification: (1) bedrock carbonates of Silurian through Devonian age, indicated by bedding scarps and lineations at or near the surface at all of the mapped areas; (2) glacial deposits that appear as compacted clay till lineations and cobble and boulder moraines with outwash features; and (3) modern sand deposits seen in thin down-drift (to the east) bedforms, sand sheets, and depositional lobes. Preferred spawning substrate—clean cobble and gravel deposits with adjacent deep water—is present in sections of all mapped areas. However, laser data cannot discern cleanliness, and video data indicate the cleanliness on this substrate may be compromised by recent algal and mussel growth.