Stable Isotopes and Movement of Walleye Change Following Ecological Shifts Driven by Dreissenid Mussels

Abstract

The Great Lakes support some of the most productive fisheries for Walleye Sander vitreus in North America, although system-level change from overexploitation, pollution, and invasive species has dramatically changed these fisheries over time. More recently, the widespread establishment of dreissenid mussels (zebra mussel Dreissena polymorpha and quagga mussel D. bugensis) has strongly altered energy flow by sequestering nutrients in nearshore benthic habitats, thereby influencing primary, secondary, and prey fish production with implications for Walleye. While the impacts of dreissenids on the open-water food web are well established, little is known about their influence on fish populations occupying nearshore or embayment habitats. In this study, we tested the hypothesis that ecosystem changes resulting from dreissenid mussels have altered the stable isotope ratios and displacement of Walleye in Little Bay de Noc, an embayment of Lake Michigan. Retrospective isotope analysis of fin spines over a 31-year time series coincident with the invasion of dreissenid mussels suggests that alterations in energy dynamics have increased Walleye reliance on nearshore benthic energy. From reports of jaw-tagged Walleye caught over the same time period, we found significant temporal changes in Walleye displacement distances from the tagging site that were strongly size dependent following the invasion of dreissenid mussels. These results potentially suggest that the spatial distribution of large Walleye shifted in response to prey availability or habitat conditions. Additionally, sex-specific differences in Walleye displacement indicate that females move greater distances than males, possibly driven by higher energetic and reproductive demands. Our findings suggest that the largest Walleye are seasonally leaving Little Bay de Noc, potentially altering the dynamics of the sport fishery in Green Bay and impacting management programs that occur across state lines.Walleye Sander vitreus are an economically and ecologically important apex predator throughout the Great Lakes (Schmalz et al. 2011;Pothoven et al. 2017). Historically, the most productive Walleye fisheries in North America came from the Great Lakes, including Lake Michigan (Schneider and Leach 1976;Schmalz et al. 2011), but the combined effects of overexploitation, pollution, and invasive species led to large population declines

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

“…Multiple symposium presentations (e.g., Brandt et al 2022;Lawson et al 2022;Whitinger et al 2022; all in this special section) highlighted the complexities of multifaceted ecosystem changes and their challenge to percid management, which were also apparent in the review completed by Hansen et al (2022). Several presentations chronicled trends in the Great Lakes and tributaries where multispecies introductions (both intentional and unintentional), exploitation, water quality and habitat degradation, and remediation efforts have led to a complex interaction of food web, habitat, and harvest changes and their effects on percid populations (Fielder and Baker 2019;Skolte et al 2022;Whitinger et al 2022;Zorn and Kramer 2022).…”

“…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.…”

“…and Cyprinus spp. ), 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).…”

“…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; Whitinger et al. 2022; Zorn and Kramer 2022). The unprecedented decline in the Walleye population of Mille Lacs Lake, Minnesota, related to water clarity, water temperature, and harvest (Hansen et al.…”