Walleye Population Responses to Experimental Exploitation in a Northern Wisconsin Lake

Abstract

Understanding how fish populations respond to exploitation is critical for sustainable fisheries management. Walleye Sander vitreus have been exploited by tribal spear and angling fisheries in the Ceded Territory of Wisconsin (CTWI) since 1985, and harvest in individual lakes has been regulated using a 35% adult exploitation limit reference point since 1990. We conducted a 35% annual adult Walleye exploitation experiment (1993–1997: baseline exploitation at ~13%; 1998–2008: 35% exploitation) on Big Crooked Lake, Wisconsin, to test for responses in adult, male, female, age‐0, and age‐1 density and sex‐specific mean length at age and proportional size distribution (PSD) indices. Adjacent Wolf Lake was used as the reference system. Adult Walleye density in Big Crooked Lake declined significantly between exploitation periods and was due to the experiment. Adult Walleye density declined from about 16 to 10 fish/ha and was about 7 fish/ha during 2001–2008. Male density declined significantly between exploitation periods, whereas female density did not change. Age‐0 and age‐1 density did not change as a result of the experiment. Male and female mean length at age across several age‐classes increased significantly over time. The PSD indices did not change over time for males, but female PSD‐Quality and PSD‐Preferred increased significantly. Our results suggest that sustained 35% annual exploitation on the Big Crooked Lake Walleye population led to an undesirable adult density (≤7.4/ha) but improved growth. Walleye recruitment did not change in Big Crooked Lake under sustained exploitation; however, we caution that other CTWI populations may respond differently to this level of targeted exploitation. Based on our results, long‐term declines in CTWI Walleye natural recruitment and productivity, and as suggested by other independent studies, we recommend that the limit reference point be lowered to reduce exploitation and be protective of all Walleye populations in the CTWI.

Production dynamics reveal hidden overharvest of inland recreational fisheries

“…Under such a management regime, harvest limits would likely be lower for most walleye stocks but may increase for others (37). Balancing population and production parameters may improve overall stock management, not only in cases where harvest might be reduced but also in cases where a certain level of production overharvest may be desirable to reduce density and increase growth of individual fish to better achieve management objectives (39). Given that walleye stocks have undergone widespread declines (22)(23)(24) and that our assessment reveals that walleye stocks have been production-overharvested, we find that overharvest has contributed in part to the observed walleye declines.…”

Effects of Angler Harvest on Adult Muskellunge Growth and Survival in Escanaba Lake, Wisconsin, 1956–2016

“…; Schmalz et al. ; Sass and Shaw ). In general, we did not observe strong evidence for changing growth rates between the types of fishery for adult Muskellunge on Escanaba Lake.…”

“…; Sass and Kitchell ; Arlinghaus et al. ; Sass and Shaw ). Thus, we used TL (cm) and age (years) data to test whether the age structure and growth rates of the Escanaba Lake Muskellunge population differed with a potential change in the prevalence of high and low harvest.…”

Characterizing the Angling and Tribal Spearing Walleye Fisheries in the Ceded Territory of Wisconsin, 1990–2015

“…). Standardized surveys are intended to represent the range of available lake types and designed to survey all exploited populations at least once per generation time (Sass and Shaw ). Lakes were sampled in a stratified random manner, with some trend lakes identified and sampled more frequently, while others were randomly sampled across key strata (e.g., region, recruitment source).…”