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US Fish & Wildlife Service FieldNotes

Understanding Lake Trout Population Diversity at Lake Superior's Isle Royale National Park

Region 3, October 18, 2012
Ashland FWCO fish biologist Henry Quinlan compares notes and personal accounts about Isle Royale lake trout with retired commercial fisherman Stewart Sivertson.
Ashland FWCO fish biologist Henry Quinlan compares notes and personal accounts about Isle Royale lake trout with retired commercial fisherman Stewart Sivertson. - Photo Credit: n/a
The R/V Chub docked outside the Sivertson Fish Camp. Wooden boats, like the ones at left, were rowed out to lake trout spawning reefs before modern boats, motors, and electronics became available.
The R/V Chub docked outside the Sivertson Fish Camp. Wooden boats, like the ones at left, were rowed out to lake trout spawning reefs before modern boats, motors, and electronics became available. - Photo Credit: n/a
Ashland FWCO fish biologist Josh Schloesser measures lipid content of lake trout, testing the hypothesis that the different stocks of Isle Royale lake trout can be distinguised by their lipid content.
Ashland FWCO fish biologist Josh Schloesser measures lipid content of lake trout, testing the hypothesis that the different stocks of Isle Royale lake trout can be distinguised by their lipid content. - Photo Credit: n/a

In the late 1800s, commercial fisherman of Lake Superior’s Isle Royale would set out in wooden boats from their fish camps tucked away inside the protected harbors of the island, and row to their favorite fishing grounds of the open waters in hopes of catching lake trout and other species. Back then, 350 to 400 foot cotton twine nets, weighed down with stones and kept afloat by wooden floats, were set and retrieved by hand on the shallow reefs adjacent to deeper water – the spawning grounds for lake trout.

With the National Park Service, the Ashland Fish and Wildlife Conservation Office is working to delineate and describe the genetics and morphological characteristics of the spawning lake trout populations around Isle Royale National Park. Based out of one of the historic fishing camps of the Sivertson Fishery, Ashland FWCO biologists set out in the aluminum-welded R/V Chub, powered by twin 200 HP Mercury outboard engines, outfitted with radar, marine radios, and other electronics, to set gangs of multi-filament nets, weighed down with metal weights and kept afloat with plastic floats. Retrieval of these nets is with a diesel-powered, hydraulic lifter.

Biological information such as length, weight, sex, and maturity is collected for each lake trout captured. A digital photograph of each lake trout collected is also taken, which will later be used back in the lab along with computer software to help describe the morphological (i.e., body size and shape) differences of spawning lake trout. Lastly, a tissue sample is taken from each fish and preserved for later examination of the genetic makeup of each spawning lake trout population.

The lake trout has long been an iconic species at Isle Royale National Park, supporting a thriving commercial fishery prior to the establishment of the park, and for decades since a popular recreational fishery within park boundaries. Populations of lake trout from Isle Royale very likely support recreational fishing outside of park boundaries, as well. Information gathered from this project will allow U.S. Fish and Wildlife Service, National Park Service and Michigan Department of Natural Resources managers to assess the potential impacts of fishing pressure and harvest, environmental changes, or catastrophic decline due to stressors such as habitat change, invasive species, and pathogens. In addition, a greater understanding of the aquatic landscape features contributing to the diversity of lake trout populations around Isle Royale National Park will contribute greatly to lake trout restoration efforts elsewhere across the Great Lakes.

Contact Info: Mark Brouder, 715-682-6185 x11, mark_brouder@fws.gov