Minnesota’s Mille Lacs Lake is a famous and productive walleye fishery, one managed with complex and varying length limits. Regulations are set to limit total angler harvest, as the available catch must be divided between them and commercial fishermen of the Mille Lacs Band of Ojibwe and other tribes. Since anglers catch many walleyes in protected length ranges, hooking mortality must be counted in the annual allotment of total catch.

To fine-tune estimates of walleyes that died following release, the Minnesota DNR undertook a major study, involving 7,400 angling hours and a catch of 1,246 walleyes.* As suspected, mortality was lowest at cool water temperatures—virtually nil in May and October, then rising to 12 percent for July through August. When water exceeded 68°F, mortality was substantially higher.

In addition to water temperature, the type of lure used also impacted mortality: The biologists found it was lowest with crankbaits. Walleyes that were hooked deeply or bled also died at higher rates. Size of fish mattered, too: Walleyes from 12 to 24 inches were toughest, with mortality significantly higher for smaller and larger fish. Because regulations typically protect much of this midsized group, the DNR reduced its estimates of annual hooking mortality, resulting in lower annual estimates of angler take. The estimate total for the year was revised to 4 percent for 2002, 3 percent in 2003, and 4 percent in 2004, based on monthly water temperatures and the length distribution of the catch.

In this study on Mille Lacs, depth of capture didn’t seem to affect outcome—though all fish were caught in less than 33 feet and most much shallower. Mortality might be higher in waters where deeper bites prevail. Although bait hooks tended to hook walleyes deeper in the mouth than jigs, mortality was similar. Also, hook type and whether or not the line was cut did not affect mortality, though the authors noted that line-cutting may have come as a last resort, when fish were bleeding or hook removal failed.—Steve Quinn

Reeves, K. E., and R. E. Brusewitz. 2007. Factors influencing the hooking mortality of walleyes caught by recreational anglers on Mille Lacs, Minnesota. N. Am. J. Fish. Mgmt. 27:443-452.