Plasticity in Abundance and Demographic Responses of Walleye to Elevated Exploitation in a North Temperate Lake

Abstract

Knowledge of density-dependent responses of fish populations to exploitation is important for the sustainable management of fisheries and in structuring fish populations to meet angler desires. To better understand the densitydependent responses of Walleye Sander vitreus to exploitation, we conducted a 10-year, 50% annual exploitation experiment on Sherman Lake, Wisconsin, during 2007-2016. In the following order, annual exploitation goals were met through liberalized recreational angling regulations, tribal spearfishing, and physical removals (if necessary). Response variables included total and sex-specific adult density, age-0 and age-1 relative abundance, age-0 to age-1 survival, length at maturity, individual growth, and population size structure. To control for environmental and interannual influences on adult density and recruitment, unexploited Escanaba Lake, Wisconsin, was used as a reference system. Total and sex-specific adult density and age-0 relative abundance did not differ between Sherman and Escanaba lakes. Age-1 relative abundance was significantly higher and more variable under elevated exploitation compared with the reference lake. Age-0 to age-1 survival significantly increased between pretreatment and elevated-exploitation time periods. Sex-specific length at maturity significantly declined between pretreatment and elevated-exploitation time periods. Mean juvenile length at age increased, male asymptotic length declined, and the proportional size distribution of quality-sized Walleye declined between pretreatment and elevated-exploitation time periods. Our results suggest that compensatory age-0 to age-1 survival and declines in length at maturity interacted to offset elevatedexploitation effects on adult density. Likewise, density-dependent growth responses were most evident in juveniles. Although the Sherman Lake Walleye population appeared resilient to elevated exploitation, we caution that this level of long-term exploitation is likely not sustainable for most Walleye populations due to the findings of previous exploitation studies and observations of depensatory recruitment dynamics in Walleye.

Black Crappie Influences on Walleye Natural Recruitment in Northern Wisconsin Lakes

“…In addition, for three CTWI lakes with no or limited Black Crappie populations and a long‐time series of Walleye data, natural recruitment of Walleye has been consistent in the long term (Sass and Shaw 2018; Sass et al. 2021; Sass et al. 2022b).…”

Density‐dependent and environmental influences on juvenile walleye Sander vitreus (Mitchill) survivorship in northern Wisconsin lakes

“…For example, natural mortality was high for age‐0 and age‐1 walleye in naturally recruiting populations (Hansen et al, 2011; Tsehaye et al, 2016). Likewise, age‐0 to age‐1 mortality declined when a walleye population was experimentally subjected to 10‐years of 50% annual exploitation, thus releasing density‐dependent constraints on mortality (Sass, Shaw, et al, 2021). Walleye growth has also been shown to be density‐dependent, but the strength of this association has been variable among populations (Lester et al, 2014; Pedersen et al, 2018; Sass et al, 2006, 2019; Sass, Shaw, et al, 2021; Venturelli et al, 2010).…”

“…Likewise, age‐0 to age‐1 mortality declined when a walleye population was experimentally subjected to 10‐years of 50% annual exploitation, thus releasing density‐dependent constraints on mortality (Sass, Shaw, et al, 2021). Walleye growth has also been shown to be density‐dependent, but the strength of this association has been variable among populations (Lester et al, 2014; Pedersen et al, 2018; Sass et al, 2006, 2019; Sass, Shaw, et al, 2021; Venturelli et al, 2010). Often, density‐dependent growth in walleye has been most evident in juveniles (Sass, Shaw, et al, 2021; Venturelli et al, 2010), as for other species (Ridgway, 2002).…”

“…Walleye natural recruitment in some lakes in the Ceded Territory of Wisconsin (CTWI, northern third of the state) has significantly declined over time (Hansen et al, 2015, 2018; Sass, Feiner, et al, 2021; Sass, Shaw, et al, 2021), although little is known about factors influencing age‐0 to age‐1 walleye mortality. Therefore, all available age‐0 and age‐1 walleye relative abundance estimates from the CTWI during 1986–2019 were used to test for mechanisms influencing age‐0 to age‐1 mortality.…”

Special Section Overview: Effects of Ecosystem Change on North American Percid Populations

“…Symposium participants emphasized the importance of adaptive approaches to managing for resilience in the face of ecosystem changes (Blackwell et al 2022;Lawson et al 2022;Sass et al 2022; all in this special section), in which data-driven actions are taken, realistic management goals are set, uncertainties are communicated to stakeholders, and management actions are revised using an adaptive framework. Participants noted that, when possible, incorporation of appropriate experimental designs to assess novel management and/or monitoring approaches, such as replication and incorporating reference ecosystems, was important for informing adaptive management (Hansen et al 2015b).…”