AUTHORS: Braden Lensing, Wisconsin Cooperative Fishery Research Unit, University of Wisconsin-Stevens Point; Daniel Dembkowski, Wisconsin Cooperative Fishery Research Unit, University of Wisconsin-Stevens Point; Joshua Raabe, University of Wisconsin-Stevens Point; Jason Breegemann, Wisconsin Department of Natural Resources; Daniel Isermann, U.S. Geological Survey, Wisconsin Cooperative Fishery Research Unit, University of Wisconsin-Stevens Point
ABSTRACT: Previous research indicates that lake sturgeon Acipenser fluvescens recruitment is limited in the Lower Fox River below De Pere Dam. Habitat enhancements in the form of an offshore reef have been proposed to potentially improve the recruitment of lake sturgeon. However, identifying spawning habitats for other species could help to ensure that restoration efforts for lake sturgeon do not result in loss of spawning habitat for other species. The Lower Fox River supports spawning runs of walleye Sander vitreus and lake whitefish Coregonus clupeaformis, both of which support important fisheries in southern Green Bay. Our objectives are to 1) describe spatial variation in walleye and lake whitefish egg densities in the LFR below De Pere Dam to inform placement of the lake sturgeon spawning reef; 2) determine if spatial variation in egg densities are related to a suite of environmental variables (e.g., flow, depth, and substrate), 3) determine if spatial distributions of eggs are similar for walleye and lake whitefish, and 4) describe the timing (e.g., start, peak, end, and duration) of walleye and lake whitefish spawning. Heat maps generated from relative egg densities illustrate the spatial distribution of walleye and lake whitefish egg densities and reveal significant overlap in egg deposition between the two species, as well as notable overlap with three of four proposed reef locations. The 2023 lake whitefish spawning period spanned 14 days, beginning on November 8 and concluding around November 21. In contrast, the 2024 walleye spawning season lasted 38 days, commencing on March 18 and ending about April 25.
AUTHORS: Kayla Lenz, Great Lakes Indian Fish and Wildlife Commission; Aaron Shultz, Great Lakes Indian Fish and Wildlife Commission; Adam Ray, Great Lakes Indian Fish and Wildlife Commission; Carl Klimah, Mille Lacs Band of Ojibwe
ABSTRACT: Mille Lacs Lake located in the 1837 Ceded Territory in central Minnesota offers a unique site for assessing the movement of fish throughout a large temperate lake. The relative shallowness of the lake and resultant lack of a thermocline allows ogaawag (walleye Sander vitreus) to forage throughout the lake, thus maximizing their range. Ogaawag , have been impacted by the many changes happening in this system over the past several decades, resulting in a variable but overall decreasing population between 1980 and 2016, when the population seems to have plateaued. This decrease has largely been attributed to a decrease in annual recruitment from hatching to age-2, but the root cause of that recruitment problem is yet unclear. In other large lake systems, ogaawag frequently display spawning site fidelity, making them especially reliant on a relatively small spawning area. Disturbances and changes in these areas may decrease overall reproduction and decrease fry survival. Identifying and protecting these critical sites may maintain annual recruitment of Mille Lacs ogaawag. The purpose of this study was to identify ogaawag spawning sites across years, characterize habitat type, and quantify spawning site fidelity of adult ogaawag in Mille Lacs Lake. Here we examine the movements of 70 tagged adult ogaawag during the spawning periods of 2019, 2020, and 2021 to determine the proportion of ogaawag that display spawning site fidelity and which areas of the lake were “hotspots” for spawning. Using an acoustic telemetry array, we examine the relationships between sex, length, detection depth, average residence time at each receiver, and spawning site fidelity to establish patterns of behavior among ogaawag. We found that ogaawag in Mille Lacs display spawning site fidelity at high rates (96%) and identified areas with rocky and/or hard substrate, lots of wind/wave action, and that are near undeveloped shoreline to be hotspots of ogaawag activity during the spawning season. We also observed what is likely an occurrence of skipped spawning in a female ogaa. Findings from this study should be used to create new stewardship plans to protect in-lake, shoreline, and upland habitats near spawning aggregation sites in Mille Lacs Lake. These approaches may be applicable to other large lake ecosystems.
AUTHORS: Jeston Hassler, South Dakota State University; Maxwel Wilkinson, University of Wisconsin-Stevens Point; Quinnlan Smith, University of Wisconsin-Madison Center for Limnology; Joseph Mrnak, Wisconsin Department of Natural Resources-Escanaba Lake Research Station/University of Wisconsin-Madison Center for Limnology
ABSTRACT: In recent decades, some lakes in the Ceded Territory of Wisconsin (approximate northern third of the state) have experienced increasing largemouth bass Micropterus salmoides abundance coupled with declining walleye Sander vitreus abundance. These shifts in abundance have become of management concern, as largemouth bass have been hypothesized to negatively influence walleye populations through potential competitive or predatory interactions. Yet, a mechanistic understanding of these ecological interactions remains relatively unknown. As climate change continues to alter thermal habitat in northern Wisconsin lakes, understanding how warming water temperatures may influence largemouth bass and walleye interactions, specifically their consumption rates of prey items, could assist in the future management of the two species. Thus, our objectives in this study were to 1) calculate diet overlap and consumption rates of common prey items for largemouth bass and walleye in a northern Wisconsin lake and 2) simulate consumption rates of largemouth bass and walleye in predicted climate change scenarios. Our study site, Little John Lake located in Vilas Co., Wisconsin, contains a naturally recruiting walleye population and fish assemblage similar to many other northern Wisconsin lakes. We intensively sampled diets of largemouth bass and walleye in Little John Lake from May-October in 2024 and took a bioenergetics approach to estimate and simulate consumption rates of these species under climate-change scenarios. Increased rates of consumption were apparent for both species, notably of yellow perch Perca flavescens and Lepomis spp., yet walleye consumption rates slowed when water temperature began reaching their thermal tolerance. Understanding how largemouth bass and walleye consumption rates may differ under climate-change scenarios may give valuable insight into future interactions between these species in northern Wisconsin lakes.
AUTHORS: William J. Radigan, University of Nebraska; Dr. Mark Pegg, University of Nebraska; Christopher Longhenry, South Dakota Department of Game, Fish, and Parks, Dr. Cameron Goble, Alberta Environment and Protected Areas; Dr. Kevin Pope, United States Geological Survey—Nebraska Cooperative Fish and Wildlife Research Unit
ABSTRACT: Walleye Sander vitreus and Sauger Sander canadensis are both socioeconomically important sportfish species in Lewis and Clark Lake, an interjurisdictionally managed mainstem Missouri River reservoir fishery. Adult Walleye (n=136) and adult Sauger (n=82) movement patterns were assessed from March 2021 to September 2024 among four management zones corresponding roughly to quarters of Lewis and Clark Lake using acoustic telemetry. We used a multistate live-dead model approach to assess survival, detection, and movement probabilities. Walleye survival probabilities (mean 85%) varied over time. Detection (mean 81%) and movement (mean 14%) probabilities varied by zone. Sauger detection probabilities varied by zone (mean 58%), and transition probabilities varied by sex, with female Sauger more likely (mean 14%) to transition among zones than male Sauger (mean 6%). Approximately 34-44% of all Walleye and Sauger were site residents, moving less than 10 km from their tagging location over the study duration. Non-site resident male and female Sauger utilized 44-47 km of the reservoir. Female Walleye utilized more of the reservoir (58 km) than male Walleye (45 km). Walleye tagged near Fort Randall Dam utilized more of the reservoir (69-72 km) than Walleye tagged elsewhere (47 km). Exploitation estimates were derived from angler-reported tags and entrainment estimates were based on detections recorded on receivers placed downstream of Gavins Point Dam. Annual exploitation (0-19%) and entrainment (0-5%) are considerable sources of loss for adult Walleye and adult Sauger in Lewis and Clark Lake. Examination of Walleye and Sauger movement patterns and sources of loss enables fisheries managers to focus management on areas identified to be important for spawning and validates the appropriateness of maintaining current harvest regulations.
AUTHORS: Thomas S. Jones, Minnesota Department of Natural Resources Mark Luehring, Great Lakes Indian Fish and Wildlife Council Heidi Rantala, Minnesota Department of Natural Resources John M. Hoenig, Virginia Institute of Marine Sciences Patrick J. Schmalz, Minnesota Department of Natural Resources
ABSTRACT: Abundance of Walleye in Mille Lacs Lake, Minnesota, has decreased since the 1990s. Two important environmental changes likely contributed to these declines. First, water clarity increased abruptly in the mid-1990s and increased clarity continues through the present day. Second, zebra mussels and spiny waterflea invaded in the late 2000’s, leading to a 90% reduction in zooplankton. Efforts to rebuild the stock through low harvest since 2013 have met with limited success. This study used multiple approaches to compare Walleye productivity changes associated with three time periods (pre-water clarity, post-water clarity, and post-invasive species). First, we estimated annual harvestable surpluses by summing Walleye fishing mortality and the resultant change in population size estimated from statistical catch-at-age models. These data were fit to surplus production models making various assumptions about the shape of the sustainable yield curve. Second, we estimated total annual Walleye production using an instantaneous growth model. All models showed reduced production after each ecological event. Recognition of reduced productivity may have ramifications for future Walleye management in Mille Lacs Lake.
AUTHORS: Maxwel Wilkinson, Wisconsin Cooperative Fishery Research Unit, University of Wisconsin - Stevens Point; Stephanie Shaw, Wisconsin Department of Natural Resources, Escanaba Lake Research Station; Joseph Mrnak, Wisconsin Department of Natural Resources, Escanaba Lake Research Station and University of Wisconsin - Madison, Center for Limnology; Greg Sass, Wisconsin Department of Natural Resources, Escanaba Lake Research Station; Daniel Dembkowski, Wisconsin Cooperative Fishery Research Unit, University of Wisconsin - Stevens Point; Daniel Isermann, U.S. Geological Survey, Wisconsin Cooperative Fishery Research Unit, University of Wisconsin - Stevens Point
ABSTRACT: The Ceded Territory of Wisconsin is a lake-rich region that supports important tribal subsistence and recreational fisheries for multiple species. Recently, declines in walleye Sander vitreus production and recruitment, coupled with increases in centrarchid abundance (e.g., largemouth bass Micropterus salmoides and bluegill Lepomis macrochirus) have created challenges for managers in terms of maintaining desired fish community structure amidst changing environmental conditions and angler preferences. Competitive and predatory interactions between centrarchid species and walleye have been hypothesized to influence walleye natural recruitment, notably in small lakes (
ABSTRACT: Walleye (Sander vitreus) is a popular sportfish whose populations are often supported by maintenance or supplemental stocking, with most fish stocked as fry, fingerlings, or advanced fingerlings. Evaluation of stocking efficacy is important to inform decisions regarding fish stocking rates and sizes and allocating hatchery fish to locations where maintenance or supplemental stocking is most needed. Several types of artificial tags or marks can potentially be used to identify stocked fish, but many have various drawbacks. Natural chemical markers in otoliths or eye lenses offer several advantages compared to conventional tags or marks and can be used to identify stocked fish when differences between hatchery-reared and wild fish are present. However, the accuracy of these approaches for identifying Walleye stocked at either fry or fingerling sizes has not been evaluated. Thus, the objectives of this study are to assess identification accuracy for Walleye stocked as fry or fingerlings using otolith microchemistry and eye lens stable isotope analysis. Known stocked fish and fish moved between chemically distinct locations to simulate stocking were obtained from several sources. Results to date indicate that otolith microchemistry can identify Walleye stocked as fingerlings with high accuracy and that the source hatchery signature can be detected in fish stocked as early as three days post-hatch. Results of this study will provide guidance regarding applications of otolith and eye lens chemistry techniques to assess contributions of stocking and natural reproduction to Walleye populations and relative efficacy of stocking fish at varied sizes.
AUTHORS: Levi Suchla, University of Minnesota; Lynn Waterhouse, University of Minnesota/U.S. Geological Survey
ABSTRACT: Mille Lacs Lake is an economically, recreationally, and culturally significant fishery, with Walleye being one of the the main targets for anglers. Over the past 30+ years, numerous biotic and abiotic changes have occurred within the lake and have had an impact on the fishery. This project aims to explore what factors have had the biggest influence on the body condition of walleye, understand the impact of some aquatic invasive species that are present in the lake, and determine the trends and shifts in walleye body condition and growth over time in relation to changing conditions.
AUTHORS: Caleb J. Branam, Michigan State University; Holly S. Embke, Midwest Climate Adaptation Science Center, U.S. Geological Survey; Chris L. Cahill, Michigan State University
ABSTRACT: A key challenge in inland fisheries is assessing numerous lakes across vast landscapes within an agency’s jurisdiction given limited resources. To reconcile this, a variety of data-limited methods have been developed to assess the status of inland fish populations. However, these tools often do not explicitly address the potential for population dynamics, or they make strong assumptions that a given population or stock is at equilibrium. Furthermore, these assessment tools are rarely simulation tested in inland fishery settings to determine their efficacy. Without knowing how these methods perform when confronted with simulated dynamics where truth is known, the effectiveness of such tools remains uncertain. Our objective was to evaluate how commonly used assessment methods for Walleye Sander vitreus performed when tested against simulated data. To achieve this, we developed an age-structured simulation model for Walleye and then evaluated the performance of the following commonly used assessment methods: mark-recapture, catch per unit effort as an index of relative abundance, size-structure indices as an index for population status, and production-based dynamics as an index of population status. This presentation will lay out the research plan for our study, present initial results for at least one assessment method, and touch briefly on the implications of potential results.
