Factors influencing the hooking mortality of walleyes caught by recreational anglers on Mille Lacs, Minnesota

Recent implementation of size-based regulations in recreational fisheries for walleye Sander vitreus have led to more released walleyes and presumably to more losses of released fish. We conducted this study to estimate hooking mortality in Mille Lacs, Minnesota, and to determine factors that influence the survival of released walleyes. Volunteers and Minnesota Department of Natural Resources employees sampled walleyes with common angling methods in 2003 and 2004 on Mille Lacs (n 1,246). Simple hooking mortality rates ranged from 0% (95% confidence interval = 0-1.8%; n 204) in May, when lake water temperatures were less than 20 degrees C, to 12.2% (9.2-15.9%; n 392) in the July-August period, when lake water temperatures were at least 20 degrees C. We used logistic regression within generalized linear or additive models to determine influential variables. Hooking mortality was most associated with water temperature, bleeding, fish length, hook location, and fish floating upon release. Mortality increased as the water warmed above 18 degrees C and was higher for fish that bled at temperatures less than 24 degrees C but similar for both bleeding and nonbleeding fishes at temperatures of 24 degrees C or more. Fish hooked in the throat or stomach died at higher rates than fish hooked in the jaw, inner mouth, or gills and those that were externally foul-hooked, especially when they were smaller. Although fish of medium length (300-600 mm) were more likely to be deep hooked, they died less frequently than walleyes of other lengths. Cutting the line did not significantly improve survival in deeply hooked fish. Mortality was similar between live bait jigs and live bait regular hooks. Most observed hooking mortality was caused by damage to major internal organs. Hooking mortality is minimized when anglers fish in cool water, use active fishing methods, and catch medium-length walleyes.