Assessing abundance of centrarchids and juvenile Yellow Perch in northern Wisconsin lakes with different Walleye recruitment histories

Abstract

Walleye Stizostedion vitreum recruitment in some northern Wisconsin lakes has declined because of recruitment bottlenecks occurring at or before mid-July and these declines have coincided with increases in adult Largemouth Bass Micropterus salmoides abundance. Increased abundance of adult Largemouth Bass may be an indicator that abundance of juvenile Largemouth Bass and other centrarchids has increased. However, standard sampling gears used by the Wisconsin Department of Natural Resources do not effectively sample fish < 100 mm total length (TL) making it difficult to evaluate trends in juvenile centrarchid abundance. These small centrarchids may interact with larval Walleye through predation or competition. Yellow Perch Perca flavescens are another important component of these fish communities, yet data needed for indexing trends in perch recruitment are not available because targeted sampling is not conducted. Consequently, the objectives of my research were to determine if: 1) sampling precision, efficiency, and length and age frequency distributions of centrarchids and juvenile Yellow Perch varied among multiple sampling gears that might be used to target fish < 100 mm TL; 2) a qualitative index of small fishes based on visual assessment during electrofishing accurately reflected overall abundance of fish ≤ 75 mm TL; 3) Walleye recruitment success was related to current relative abundance estimates for centrarchids and juvenile Yellow Perch; and 4) Walleye recruitment success was related to historical measures of centrarchid and juvenile Yellow Perch relative abundance. In 2019 and 2020, eleven lakes in northern Wisconsin were sampled using mini-fyke nets, cloverleaf traps, modified boat electrofishing, and electrofishing from a boat using a hand-held probe. Modified boat electrofishing is similar to standard boat electrofishing except boat speed was reduced and netters focused on capturing small fish (≤ 150 mm TL) and used dip nets with finer mesh (4.76-mm). No gear was effective at sampling Black Crappie Pomoxis nigromaculatus, Rock Bass Ambloplites rupestris, and Pumpkinseed Lepomis gibbosus. Mini-fyke nets were the only gear that were able to catch ≥ 50 Smallmouth Micropterus dolomieu and Largemouth Bass in more than two lakes. For Bluegill Lepomis macrochirus and Yellow Perch, modified boat electrofishing had the most precise catch per effort (CPE) and required the fewest number of samples to detect a 50% change in mean CPE; however, cloverleaf traps required fewer 8-h workdays to detect a 50% change in mean CPE. These gears may be effective to index year-class strength of these species, but future research will need to determine if relative abundance of fish captured in these gears can accurately predict year-class strength. A qualitative approach for estimating abundances of small fish (≤ 75 mm TL) using observations made by netters while boat electrofishing did not significantly correlate with summed CPE estimates for overall abundance of small fish, but did significantly correlate with individual estimates of Yellow Perch and Lepomis spp. Probability of Walleye recruitment success was not related to relative abundance of centrarchids or Yellow Perch in contemporary sampling (2019–2020). Probability of historical Walleye recruitment success from 1997–2006 was positively related to relative abundance of Yellow Perch and Smallmouth Bass in mini-fyke net sampling conducted from 2000–2006. Our results indicate that additional effort to understand Yellow Perch and Walleye relationships and Yellow Perch recruitment trends is warranted and this information could contribute to a better understanding of Walleye recruitment trends and fish community shifts in north temperate lakes.