Characteristics of an Introduced Walleye Population with Implications for Suppression

Abstract

The management of introduced fishes, including Walleye Sander vitreus, whether for control or enhancement, requires understanding of population dynamics at the invasion front. Walleye recently established in the Pend Oreille basin, Idaho, threaten the existing salmonid‐based fish community and associated recreational fishery. Therefore, the objectives of this study were to describe population growth and associated life history characteristics. Walleye were sampled in October of 2011, 2014, and 2017 using a standardized gill netting survey protocol to describe trends in relative abundance and evaluate population dynamics. Relative abundance increased exponentially from 1.4 to 4.3 fish/net over the 6‐year monitoring period. This population was characterized by fast somatic growth, robust body condition, and early age at maturity at or near the biological maxima for Walleye. Among the survey years, mean length at age 2 varied for female (359–441 mm) and male (358–426 mm) Walleye and relative weight varied from 91 to 98. The sampled Walleye matured at 1 to 4 years of age, and recruitment became more consistent as abundance increased. These density‐dependent metrics suggest that the Walleye population is still at low density relative to carrying capacity. The information that was gained from this study was used to better understand potential risks and guide management decisions related to experimental population suppression that is now underway. Suppression under these conditions must overcome the recruitment capabilities of the population. We conclude that natural mortality is likely regulated by density‐dependent processes. Therefore, at current (low) density, fishing mortality may be entirely additive and compensation is unlikely to further complicate management.

Forensic geochemistry identifies the illegal introduction of Walleye into Lake Cascade, Idaho

“…In Idaho, great effort has gone into preventing Walleye from spreading into new watersheds because once they are initially introduced, their population can rapidly increase and become difficult if not impossible to eradicate (Ryan et al 2021). Across the western United States, there are many examples of prized sport fisheries being disrupted by illegal Walleye introductions (e.g., McMahon and Bennett 1996;Baldwin et al 2003;Johnson et al 2017).…”

“…This popularity has led to their introduction into areas where they are not native, such as in the lakes and waterways of the intermountain western USA. In many of these locations where they become established outside of their native range, Walleye drastically alter the existing fisheries as prolific predators (Yule et al 2000;Baldwin et al 2003;Quist et al 2005;Ryan et al 2021). Lake Cascade is a reservoir that is known for providing a world-class recreational fishery for Yellow Perch Perca flavescens, which draws more than 250,000 h of angling effort each year (Idaho Fish and Game, unpublished data).…”

Simulated effects of imperfect sterile sport fish stocking on persistence of fertile fish in new exploited populations

“…Age 5 (sexes combined) represented baseline conditions (Hansen et al 1998), but maturation could occur earlier or later. Therefore, we simulated populations maturing (sexes combined to align with methods of Hansen et al 1998) as early as age 3—the most extreme scenario reflecting an invasive Walleye population at their invasion front (e.g., Ryan et al 2021)—to as late as age 7 to bracket the plausible range for Colorado reservoirs based on observed variation in growing degree‐days (Baccante and Colby 1996; Venturelli et al 2010).…”

An evaluation of the relative size, body condition, and survival of triploid Walleye in the wild

“…2009, 2017; Clancy and Bourret 2020; Ryan et al. 2021) may generate an increased interest in the stocking of triploid Walleye. However, there is a lack of basic information regarding the biology and poststocking performance of triploid Walleye—information that is essential for effective management and for guiding policy regarding their use.…”

“…This includes stocking triploids to (1) diversify recreational angling opportunities, (2) deter illegal fish stocking, (3) limit the possibility of new Walleye populations becoming established in sensitive areas, and (4) possibly interfere with reproduction in unwanted diploid populations (Johnson et al 2009;Feindel et al 2010;Farrell et al 2022a;Hansen et al 2023). Continuing invasions of Walleye throughout the western United States (McMahon and Bennett 1996;Rahel 2004;Johnson et al 2009Johnson et al , 2017Clancy and Bourret 2020;Ryan et al 2021) may generate an increased interest in the stocking of triploid Walleye. However, there is a lack of basic information regarding the biology and poststocking performance of triploid Walleyeinformation that is essential for effective management and for guiding policy regarding their use.…”