Assessing Minnesota’s Changing Yellow Perch Populations Using Length‐Based Metrics

Abstract

Catch rates of Yellow Perch Perca flavescens in standard gill-net surveys conducted by the Minnesota Department of Natural Resources have declined since 1970, but it is unclear whether this trend was due to reduced abundance or to changes in size structure affecting catchability. Because the minimum capture length of standard gill nets may limit effective sampling of some populations, the objectives of this study were to determine if length-based metrics could be used to characterize populations and their susceptibility to standard gill nets, if these metrics were correlated with a suite of abiotic and biotic variables, and if temporal trends in these metrics were evident. Data were collected from a broad size distribution of Yellow Perch sampled with standard gill nets, boat electrofishing, and small-mesh gill nets in 17 lakes. Estimated length at 50% maturity (L50) for females varied up to 100 mm across lakes, with values as small as 70 mm documented in some populations. Female L50 from supplemental gears was significantly positively correlated with the average length of the 15 largest fish (L max ) from all gears, and both of these metrics were positively correlated with standard gill-net catch. Exploratory analysis of female L50 indicated that this metric was positively correlated with latitude and lake size and negatively correlated with water clarity. Additionally, a statewide analysis of L max conducted with standard gill-net data from over 1,000 lakes found significant declines during the past 25 years, indicating that populations in Minnesota have likely shifted towards a smaller size structure, reducing catchability in standard gill nets. These results indicate that standard gill nets were ineffective for sampling some Yellow Perch populations and that length-based metrics such as L50 and L max can be used to infer catchability in standard gear and to monitor populations through time.Yellow Perch Perca flavescens are a percid species of management interest in the Upper Midwest region of the United States, occupying diverse lentic systems from the Great Lakes to glacial ponds. Yellow Perch fulfill dual ecological roles as a primary forage species for top predators, such as Walleye Sander vitreus (Johnson and Hale 1977) and Northern Pike Esox lucius (Pierce 2012), but are also piscivorous and targeted for harvest at larger

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

“…2014), and the importance of such data sets was demonstrated in many symposium presentations (Holbrook et al. 2022; Lawson et al. 2022; Whitinger et al.…”

“…), Rainbow Smelt Osmerus mordax, and Round Goby Neogobius melanostomus, have altered food webs and energy flow, with significant-and often detrimental -ramifications for percid populations in many North American ecosystems (Barbiero and Tuchman 2004;Mercado-Silva et al 2007;Bunnell et al 2014;Sass et al 2014;Hansen et al 2020;Whitinger et al 2022, this special section; Zorn and Kramer 2022, this special section). Historical anthropogenic habitat degradation and subsequent remediation efforts have resulted in changes in water quality in many freshwater ecosystems, with implications for percid populations and the sampling methods used to monitor population status (Hayward and Margraf 1987;Stapanian et al 2009;Bacheler et al 2011;Gibson-Reinemer et al 2017;Hansen et al 2019;Holbrook et al 2022, this special section). In addition, warming water temperatures, changing water quality, and future climate projections have influenced and may continue to influence freshwater fish communities through alterations in physical habitat availability (Magnuson et al 1990;Ferguson 2004;Dippold et al 2020;Blackwell et al 2022, this special section;Skolte et al 2022, this special section;Smith et al 2022, this special section).…”

“…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). Long-term data sets, such as those collected as part of routine agency monitoring programs, can be used to identify the effects of and interaction between multiple stressors of fish communities (Ivan et al 2014), and the importance of such data sets was demonstrated in many symposium presentations (Holbrook et al 2022;Lawson et al 2022;Whitinger et al 2022;Zorn and Kramer 2022).…”

“…2022; Holbrook et al. 2022) and consideration of expanding standard sampling techniques (Holbrook et al. 2022).…”

“…Stocking to rehabilitate and support Wisconsin Walleye fisheries has yielded mixed success (Lawson et al 2022). Additionally, the importance of Yellow Perch as prey for larval Walleye in northern Wisconsin lakes (Gostiaux et al 2022) and indications of declining Yellow Perch populations in Minnesota (Bethke and Staples 2015) have led to increased efforts to sample and characterize Yellow Perch populations in both states (Brandt et al 2022;Holbrook et al 2022) and consideration of expanding standard sampling techniques (Holbrook et al 2022). While this research has helped to reduce the number of viable hypotheses for Walleye recruitment declines, the direct mechanisms have yet to be determined.…”