Latent mortality of walleye and lake whitefish discarded from commercial and recreational fisheries in Green Bay, Lake Michigan

LMORT

January 2025 - December 2028

The Wisconsin waters of Green Bay support an important commercial trap net fishery for lake whitefish with effort that typically exceeds 2,500 pot lifts per season. In addition to other species, bycatch in the commercial fishery includes sublegal lake whitefish (< 432 mm) and walleye, which must be discarded. Lake whitefish of legal size are also discarded as high-grading is a common practice in the commercial fishery. Increases in lake whitefish abundance in Wisconsin waters of Green Bay over the last decade, coupled with declines in whitefish stocks in Wisconsin waters of Lake Michigan proper, have led to more commercial quota being allocated to Green Bay and has resulted in increased trap net effort and subsequent increases in bycatch and discard rates of whitefish and walleye. Understanding the extent of latent mortality after trap-net capture has important implications for informing upcoming management decisions regarding commercial fishing effort and quota allocation to minimize fishery impacts on nontarget species or sizes. Furthermore, lake whitefish and walleye support popular recreational fisheries and targeted annual effort for the combined fisheries typically exceeds 800,000 angler hours. Understanding the extent of latent mortality of walleye and lake whitefish discarded after recreational hook-and-line capture would help inform harvest management approaches and potential regulation changes for the recreational fisheries. Multiple user groups (i.e., commercial and recreational fishers) “competing” for the same resources has resulted in perceived conflicts and concerns over potential adverse impacts on fishery resources through high mortality of discarded fish. Wisconsin DNR fishery managers’ ability to respond to these concerns and mitigate user group conflict is limited as little information exists regarding mortality of lake whitefish and walleye released after capture from either fishery type. We propose to use acoustic telemetry to estimate latent mortality of walleye and lake whitefish discarded from commercial and recreational fisheries and determine if species-specific latent mortality rates differ between fishery types in Wisconsin waters of Green Bay. A telemetry-based approach is advantageous for addressing these questions in Green Bay because receiver infrastructure for detecting fish affixed with transmitters is already in place at a bay-wide scale in support of other GLFWRA-funded projects. Furthermore, findings from a pilot study conducted during August-September 2022 suggest that using acoustic telemetry with our proposed tagging and monitoring methods is a viable approach for addressing our research objectives. This is a tag-only project.

• Provide estimates of latent mortality for walleye and lake whitefish discarded from commercial and recreational fisheries in Wisconsin waters of Green Bay.
• Determine if estimates of latent mortality for walleye and lake whitefish vary between commercial and recreational fisheries.

• Daniel Dembkowski (University of Wisconsin Stevens Point) - dan.dembkowski@uwsp.edu

• Wisconsin Cooperative Fishery Research Unit
• Wisconsin Department of Natural Resources