Current Research

Can Angler Harvest Be Used to Reduce Largemouth Bass Populations in Northern Wisconsin Lakes?
Principal Investigators: Daniel Isermann, Michael Hansen, Jonathan Hansen (WDNR)
Graduate Student: Kaitlin Schnell

Catch and ReleaseLargemouth bass Micropterus salmoides abundance has increased in many northern Wisconsin lakes over the last decade and this has caused some concern for anglers and biologists due to potential negative interactions with other popular sportfish such as walleyes Sander vitreus.  The Wisconsin DNR has liberalized black bass harvest regulations on some northern Wisconsin lakes in an effort to reduce bass abundance. However, available information suggests that exploitation of largemouth bass is generally low (i.e., < 10%) and it is unclear whether angler harvest will be sufficient to actually affect bass abundance in these lakes. Furthermore, several recent studies suggest that anglers voluntarily release most of the black bass they catch, so liberalization of harvest regulations may not result in substantial increases in bass exploitation. Our primary objectives for this study are to determine if: 1) angler harvest can be used to effectively reduce largemouth bass populations in some northern Wisconsin lakes and 2) certain harvest regulations are more likely to result in reduced largemouth bass abundance in these lakes. Currently, we are obtaining population estimates and demographic information for largemouth bass populations in several northern Wisconsin lakes; this information will be used in stage-structured modeling exercises to address our two research objectives. Additionally, we are collecting scales, otoliths, dorsal spines, and anal spines from largemouth bass to examine differences in age estimates and associated precision among structures. This project is funded by the Wisconsin DNR and sampling will continue through the summer of 2014.

Largemouth Bass in Wisconsin Lakes: Factors Regulating Recruitment and Potential Dietary Interactions with Walleyes
Principal Investigator: Daniel Isermann, Jonathan Hansen, and Joe Hennessy (WDNR)
Graduate Student: Craig Kelling

LargemouthLargemouth bass Micropterus salmoides abundance has increased in many northern Wisconsin lakes over the last decade and this has caused some concern for anglers and biologists due to potential negative interactions with other popular sportfish such as walleyes Sander vitreus.  A previous FAC analysis (Repp 2012), showed evidence of negative interactions between largemouth bass and walleyes, but the mechanisms behind these interactions remain unknown, Furthermore, it is unclear as to what environmental factors may have contributed to increased bass abundance in many lakes. Our primary objectives for this study are to determine if: 1) hatch timing affects growth and survival of age-0 largemouth bass in Wisconsin lakes; 2) determine if timing of piscivory could affect growth and survival of age-0 bass and 3) determine if largemouth bass prey on walleye or if diet overlap occurs between the two species. Currently, we are obtaining largemouth bass and walleye diets from two northern Wisconsin lakes and we are collecting age-0 largemouth bass from several lakes across the state for estimation of hatch dates. Sampling will continue through the summer of 2014. This project is funded by the USGS and represents a collaborative effort among the FAC, Wisconsin DNR, the Center for Limnology at UW-Madison and the Wisconsin Cooperative Fishery Research Unit at UWSP.

Stock Characteristics of Lake Whitefish in Lake Michigan
Principal Investigators: Daniel Isermann, Brian Sloss, Justin VanDeHey, Michael Hansen
Graduate Student: Matt Belnap


WhitefishLake whitefish Coregonus clupeaformis support the largest remaining commercial fishery on Lake Michigan and serve an important role in food web dynamics and energy transfer within the lake. Previous work conducted by the Wisconsin Cooperative Fishery Research Unit demonstrated that six distinct genetic stocks of lake whitefish exist in Lake Michigan and that a mixed fishery for lake whitefish does exist within the lake. However, it is not fully known whether population dynamics and demographics vary among these stocks, which could make some stocks more susceptible to overfishing than others. Our objectives for this project are to: (1) determine if capture location during October accurately delineates genetic stock structure of lake whitefish in Lake Michigan in relation to genetic stock, sampling period, gender, or status of gametes; 2) determine if body condition, growth, age structure, gonadosomatic index (GSI), fecundity, egg size, and maturation schedules differ among genetic stocks of lake whitefish in Lake Michigan and 3) determine if stocks would likely respond differently to exploitation based on differences in biological characteristics. Fish for the project will be obtained from commercial and tribal fishers from around the lake. This project is funded by the Great Lakes Fishery Commission and represents a collaborative effort between the FAC, the Wisconsin Cooperative Fishery Research Unit, the Wisconsin and Michigan Departments of Natural Resources, and several tribal organizations around Lake Michigan. Sampling for this project will begin in October 2012 and will continue through October 2013.

Statewide Evaluation of Calcified Structures Used for Walleye Age Estimation
Principal Investigators: Daniel Isermann, Ron Bruch, and Connie Isermann

WalleyeBiologists in Wisconsin and elsewhere still employ a variety of calcified structures (e.g., scales, spines, otoliths) to estimate the age of walleyes, despite several studies suggesting that certain methods are imprecise or inaccurate. In an effort to provide guidance to biologists regarding the potential use of these structures, the Wisconsin DNR’s Fish Age Task Group solicited samples of walleyes from all over the state. Currently we have collected scales, otoliths, dorsal spines, and anal fin spines from more than 300 walleyes from 5 different locations in the state of Wisconsin. All structures will be photographed and interpreted by a panel of readers to assess precision of age estimates and to determine the extent to which ages from other structures reflect sectioned otolith ages, the method considered to be most reliable for estimating the age of walleyes and many other species of fish. Additional samples of fish will be collected in 2012-13 and images of all structures will be available on the FAC website as they are completed.

Predicted Effects of Exploitation and Length-Based Harvest Regulations on Lake Sturgeon in the White Rapids Section of the Menominee River, Wisconsin
Principal Investigators: Daniel Isermann, Mike Donofrio (WDNR), and Ed Baker (Michigan DNR)

SturgeonOverharvest is a persistent concern for lake sturgeon Acipenser fulvescens stocks that support recreational fisheries. Consequently, selecting harvest regulations for these fisheries is an important process for fishery managers. The Menominee River that borders the states of Wisconsin and Michigan currently supports some of the largest stocks of lake sturgeon associated with Lake Michigan and some of these stocks have supported hook-and-line fisheries for decades, but fishery managers are still uncertain as to how angler harvest and changes in harvest regulations affect the sustainability of these stocks. Our objectives were to: 1) determine if current and historic levels of exploitation significantly affect lake sturgeon recruitment and population demographics in the White Rapids section of the Menominee River and 2) determine the potential effects of length-based harvest regulations on lake sturgeon exploitation and recruitment. Lake sturgeon were captured using pulsed DC boat electrofishing on 9 different dates between 12 April 2012 and 9 May 2012 (Table 1). Both the Wisconsin and Michigan Departments of Natural Resources assisted with this sampling. During April-May 2012 we captured 228 lake sturgeon that ranged in total length from 13.5 to 62 inches. We are currently in the process of estimating the population size of lake sturgeon in the White Rapids section using Program MARK. After estimates of population size and age structure are complete, we will begin age-structured simulation modeling to determine the effects of exploitation and length limits on lake sturgeon in this section of the river. This project is funded by Wisconsin Energies-Wilderness Shores Mitigation and Enhancement Fund. The project is a collaborative effort between the FAC, the Wisconsin Cooperative Fishery Research Unit, and the Wisconsin and Michigan DNR.

Evaluation of Harvest Regulations for Crappies and Yellow Perch in Wisconsin
Principal Investigators: Daniel Isermann, Michael Hansen, Nancy Nate, Jonathan Hansen (WDNR)
Graduate Student: Kyle Mosel

Black CrappieBlack crappie Pomoxis nigromaculatus and yellow perch Perca flavescens support popular, harvest-oriented fisheries across most of their range, including Wisconsin. Harvest in these fisheries is typically regulated using daily creel limits and, in some cases, minimum length limits. Several previous evaluations have suggested that the effectiveness of these harvest regulations in meeting management objectives varies among fisheries. Harvest regulations for black crappies and yellow perch in Wisconsin have not been thoroughly evaluated. The objectives of this project were to determine if: 1) species-specific reductions in daily creel limits or statewide minimum length limits could reduce harvest of yellow perch and black crappie in Wisconsin and 2) reductions in daily creel limits or implementation of minimum length limits might improve yield, harvest, and size structure of black crappie and yellow perch fisheries within the state. We used existing data on harvest and growth rates along with Beverton-Holt equilibrium yield models to address these objectives. Current harvest data suggests that to effectively reduce harvest, daily creel limits would need to be 5 fish a day or less for both black crappies and yellow perch. However, drastically reducing the daily creel limit from 25 to 5 fish per day may be socially unacceptable. Minimum length limits are most likely to be effective if natural mortality is low for black crappie and yellow perch populations in Wisconsin, but most black crappie populations had natural mortality estimates greater than 0.30. To effectively reduce harvest using statewide minimum length limits, length limits would need to be 229-mm or greater for black crappies and 203-mm or greater for yellow perch. However, length limits may not be reasonable on a statewide scale due to the large variation in growth rates for both species and the prevalence of high natural mortality within crappie populations.  Download Thesis.

Investigating interactions between walleye and black bass in northern Wisconsin lakes.
Principal Investigators: Daniel Isermann, Michael Hansen, Jonathan Hansen (WDNR)
Graduate Student: Andrew J. Repp
 
Abstract–Walleye and black bass are popular game fish, walleye being the most intensively stocked and harvested fish species in Wisconsin, while black bass are the most popular game fish species in the nation. Current management practices in Wisconsin often seek to simultaneously enhance populations of these species in likes where both occur. Past studies have indicated that this may not be a feasible goal, because the species may interact negatively. My objective was to determine if available evidence supported the conclusion that walleye and black bass interact in northern Wisconsin lakes. I used data collected from 1,862 northern Wisconsin lakes over 74 years to create indices of abundance, growth, population size structure, and recruitment. I used rank correlation and measurement error ratio regression to test for relationships between these population demographics to determine if black bass and walleye populations may interact. I determined whether a high abundance of one species is significantly related to any population demographic of the others. I found a significant negative relationship between largemouth bass abundance and walleye abundance, a significant positive relationship between largemouth bass abundance and walleye growth and size structure, and a significant negative relationship between largemouth abundance and walleye recruitment. These results may be indicative of largemouth bass preying on juvenile walleye. I found no clear or consistent relationship between walleye and smallmouth bass. These findings suggest that management practices for all three species may need to be changed to account for the impossibility of enhancing populations of walleye and largemouth bass in one lake simultaneously. I recommend further study to more precisely determine the extent of the interactions between walleye and largemouth bass.  Download Thesis

Age Estimation Survey

Abstract.– An online survey was created to assess current protocols, practices, and needs related to estimating fish age and applying knowledge of fish population age structure to fisheries management decisions.  The survey was available online to Wisconsin Department of Natural Resources (WDNR) Fisheries Management and Research staff from September 29–November 7, 2010 and covered topics such as techniques, quality assurance protocols, inventories of existing hard structures, inventories of populations of known-age fish, equipment needs, and research priorities. The Fisheries Analysis Center (FAC) at UW-Stevens Point will be coordinating activities related to the development of educational materials and training modules, building reference collections, and creating a website to facilitate the exchange of information on current age estimation techniques, quality assurance practices, literature, as well as the development of a library of images of known-age fish.  An age estimation workshop is planned for June 2011.  The results of this survey will also be used to suggest prioritization of equipment purchases and upgrades in regional offices.  Download full report

Trout Regulations Evaluation

Abstract.– Wisconsin trout stream regulation categories based on a stream classification system have been used in Wisconsin since the early 1990s, but these regulations have not been thoroughly evaluated.  We used electro-fishing survey data collected from 2,879 sites on 1,102 Wisconsin trout streams during 1992–2010 to determine if brook and brown trout relative abundance of different length groups differed among streams with different harvest regulations and stream size categories (small, medium, and large).   Download full report