GLIFWC survey crews and partners assess walleye hatch on 105 lakes
By Mark Luehring, GLIFWC Inland Fisheries Biologist
Oodenaang (Odanah), Wis.—Shortly after walleye hatch in the spring, walleye fry move out to the open water zones in inland lakes and feed on plankton for the first few weeks of their lives. About the time the leaves change, the small walleye have moved to near-shore habitats to feed at night on invertebrates and small fish. During this time, GLIFWC survey crews conduct electrofishing surveys to gauge the strength of the walleye year-classes on each lake.
Electrofishing boats use electrical current to temporarily stun fish, so that survey crews can net them, collect length information, and release them alive. Crews target mostly walleye under 12 inches, specifically young-of-the-year and one-year-old walleye.
Biologists use the information gathered here to evaluate year-class strength and long-term trends in natural reproduction. These surveys also provide the first look at the future of the adult walleye populations. Natural reproduction varies widely by year even on lakes with large adult walleye populations, but if fall surveys show a number of consecutive years with poor or low reproduction, biologists have advance warning that the adult population may decline.
While most of the surveys focus on lakes with natural reproduction, some fall surveys are also used to assess the contribution of stocked fish to the year-class. Stocked fish can be marked with oxytetracycline (OTC), and fish can be examined for marks to determine the percentage of stocked fish in the year-class. Survey
crews collected OTC samples from Portage Lake in Michigan and Lac Vieux Desert on the Wisconsin/Michigan border.
This fall, crews from GLIFWC, Bad River, Mole Lake, St. Croix, and USFWS surveyed 105 lakes including 13 surveyed in cooperation with Wisconsin DNR, one surveyed in cooperation with Michigan DNR, and Mille Lacs Lake surveyed in cooperation with the Fond du Lac Band. All lakes surveyed were in the 1837 and 1842 ceded territories, including 95 lakes in Wisconsin, 9 in Michigan, and Mille Lacs Lake in Minnesota. Lakes ranged in size from the 123-acre Sherman Lake to 132,516-acre Mille Lacs Lake.
A "chi miigwech" (thank you) goes to electroshocking crew members who spent their nights over a six-week time period on ceded territory lakes collecting this valuable information!
