Size- and Sex-Specific Capture and Harvest Selectivity of Walleyes from Tagging Studies

Estimates of size- and sex-specific gear selectivity are important for making informed management decisions. Sex-specific selectivity curves may be needed for two-sex statistical catch-at-age models when information about sex ratios in the catch is unavailable. We used data from three tagging programs in Minnesota and Wisconsin to estimate the size- and sex-specific selectivity of angling and spearing for Walleyes Sander vitreus. We estimated capture selectivity (the relative catchability of each component of the population) and harvest selectivity (the combined effect of capture selectivity and the decision to retain or release a fish from a given component). These components are of interest because (1) the hooking mortality of released fish contributes substantially to total mortality, so that it is important to know how harvest and release vary by size; and (2) capture selectivity is likely similar across lakes, such that data from other lakes may provide information on capture selectivity for the lake of interest, while harvest selectivity is lake specific. Estimates were obtained using generalized linear models to determine the significance of the individual and interactive effects of length and sex on selectivity. Angling capture and harvest selectivity were both greater for females than males of every length. In contrast, spearing harvest selectivity was greater for males. For both sexes, harvest selectivity for angling and spearing peaked at around 400-450mm. The capture selectivity of anglers peaked at 350-375mm. The interaction between sex and size was significant for capture selectivity for angling, with the sex effect for small fish being less than that for large fish. Above 400mm, spearing selectivity did not appear to vary with length for either sex, but at lengths below that it was lower for males. Received March 20, 2013; accepted October 29, 2013