Siscowet lake trout: Everything you need to know

This unique fish can only be found in the deepest parts of Lake Superior.

Lake trout morphotypes, including the siscowet, lean and humper lake trout. Shawn Sitar | Michigan Department of Natural Resources
Lake trout morphotypes, including the siscowet, lean and humper lake trout. Shawn Sitar | Michigan Department of Natural Resources

Lake trout, the most abundant predator in Lake Superior, is comprised of three principal forms or morphotypes that include the lean lake trout, humper lake trout, and siscowet lake trout. Siscowet can be distinguished from other forms of lake trout by their physical characteristics and presence in the deep-water region of Lake Superior.

Siscowet have a convex snout, small head, a deep body, a short, thick caudal peduncle, and high lipid content in the muscle. Siscowet typically inhabit waters greater than 250 feet in depth, feeding primarily on bottom fishes, while lean lake trout are mostly found in waters less than 250 feet deep, with some overlap in their distributions. Siscowet are most abundant in waters 300 to 600 feet deep, but have also been captured from the deepest points of Lake Superior at over a 1,000 feet. Humper lake trout are less commonly encountered than the other two forms and are mostly associated with isolated offshore reefs.

Siscowet were historically harvested for food and oil by Native Americans and early settlers. In Michigan, except for a brief period in the 1980s, siscowet have never been targeted for a fishery. Between the 1880s to present, siscowet were captured incidentally as part of the lean lake trout fishery and in the last century were targeted in deep water gill net fisheries. With successful control of sea lamprey and low fishing mortality both lean and siscowet lake trout forms have increased. In fact, the number of siscowet has increased many times more in numbers than the lean lake trout. There are now concerns that the increasing demands on prey fish by siscowet will affect the more economically valued lean lake trout.

The fat content in siscowet flesh are comprised of omega-3 fatty acids (eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]), which have significant health benefits and economic value. Fish oils are widely used in supplement capsules and added to certain food items. Michigan Sea Grant and Michigan State University Extension recently completed a study on fatty acid content in siscowet. Interest in renewed commercial harvest of siscowets for the extraction of fatty acids has initiated an effort to determine the sustainability of a fishery.

Thus the Lake Superior Technical Committee of the Great Lakes Fishery Commission has been working on a Technical Report “Synthesis of deepwater (Siscowet) lake trout in Lake Superior.” The report reviews siscowet genetics, fatty acid content, ecology, population dynamics and management in Lake Superior. A combination of literature review, recent fisheries data and modeling are used to provide an updated perspective on the ecological role of siscowet in Lake Superior, and to provide recommendations for siscowet management and research. Michigan Sea Grant and Michigan State University Extension have contributed to the section on fatty acids content of siscowet lake trout in this technical report.

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