Current Research

Principal Investigators: Daniel Isermann and Justin VanDeHey
Graduate Student: Nick Rydell
The objectives of our study are to determine if: 1) 2, 4-D herbicide treatments used to control EWM affect the abundance, diversity, and size structure of fish at different life history stages; 2) herbicide treatments affect feeding, survival, growth, and reproductive investment of selected fish species, and 3) if herbicide treatments affect diversity, abundance, and size of zooplankton. 

Principal Investigators: Daniel Isermann, Michael Donofrio (WDNR), and Ed Baker (Michigan DNR)
Our objective is to use a portable ultrasound to determine the sex and maturation status of lake sturgeon in order to improve lake sturgeon assessment, management, and research activities in the White Rapids section and other portions of the Menominee River. Specifically, we will combine the use of passive integrated transponder (PIT) technology with the ultrasound which will allow biologists to better determine population sex ratios and maturation history of individual lake sturgeon.

Principal Investigators: Daniel Isermann, Michael Donofrio (WDNR), Steve Cooke (Carleton College), Ed Baker (Michigan DNR), Rob Elliott (USFWS)
Graduate Student: Josh Schulze
Our research objectives are to determine: 1) if adult lake sturgeon passed upstream return downstream to the lower Menominee River or Green Bay within 1 or 2 years of passage; 2) if adult lake sturgeon have the opportunity to spawn at least once above Park Mill Dam within 1-2 years after passage; 3) if spawning opportunity, downstream return rates, and use of the downstream fishway at Park Mill Dam are related to timing of passage, time elapsed since passage occurred, month of year, flow or temperature conditions, or in relation to fish attributes such as sex, length, and maturation status and 4) if the number, length, and sex of fish passed upstream and timing of passage can be manipulated to maximize the number of eggs deposited above Park Mill dam by fish that were passed upstream.

Principal Investigators: Daniel Isermann, Jonathan Hansen (WDNR), Joe Hennessy (WDNR), Jared Myers (WDNR), Janice Kerns 
Over the past several years, we have been assessing TRAFx ® Vehicle Counters buried at Wisconsin boat ramps as alternative means of estimating angler effort.  

Principal Investigators: John Lyons (WDNR), Daniel Isermann, Kaitlin Schnell, Connie Isermann
Our objective is to determine if abiotic and biotic variables affect growth rates, recruitment patterns, and the age and size structure of cisco populations in Wisconsin.

Principal Investigators: Daniel Isermann, Nancy Nate, Gretchen Hansen (WDNR)  
We determined if variation in biological performance indicators (BPIs; ω, mean total length (TL) at age 3, mean age at 50 cm TL, age classes present, age class diversity [H], catch-per-effort [CPE] of age-0 walleyes, coefficient of variation in age-0 CPE, targeting angler catch rate, and the mean TL of the 10 smallest mature females) observed for walleye populations in northern Wisconsin could be explained by exploitation rates while also considering adult density, lake surface area, recruitment category (naturally-reproducing or stocked), latitude, and longitude as additional explanatory variables.  We also determined if BPIs could be used to identify walleye populations that have experienced relatively high exploitation rates (i.e., rates ≥ upper quartile values) in each recruitment category. 

Principal Investigators: Daniel Isermann and Michael Donofrio (WDNR)
Graduate Student: Joshua Schulze
Our objectives are to determine if: 1) smallmouth bass freely move among river sections within an impoundment; 2) smallmouth bass occupy relatively small overlapping home ranges during fall and winter periods and 3) more stringent harvest regulations are predicted to improve the number of smallmouth bass ≥ 16 inches total length (TL).

Principal Investigators: Daniel Isermann, Ryan Koenigs (WDNR), Ron Bruch (WDNR)
Graduate Student: Zachary Snobl
Our objective is to determine if sub-adult lake sturgeon selectively occupy certain habitats in the lower Wolf River based on substrate, depth, and presence of coarse woody debris.  

Principal Investigators: Daniel Isermann, Gretchen Hansen (WDNR), Jonathan Hansen (WDNR)
Graduate Student: Hadley Boehm
Our primary objectives are to determine if: 1) larval and juvenile walleye abundance, survival, foraging success, diet composition, and growth vary among populations; 2) predation by northern pike, black crappies, bluegill, and yellow perch could affect walleye recruitment; 3) availability of suitable optical and thermal habitat varies among lakes in relation to walleye recruitment patterns and 4) zooplankton abundance, community composition, and size structure varies in relation to  larval growth and survival and subsequent recruitment. Additionally, we will identify when age-0 walleyes enter the littoral zone to improve model projections regarding the effects of predation on walleye year class strength.    
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)
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.

​Recently Completed Research​

Principal Investigators: Daniel Isermann, Jonathan Hansen (WDNR), and Dave Fulton (U. S. Geological Survey, Minnesota Cooperative Wildlife Research Unit)
Our objective was to design and implement a survey to ascertain angler preferences related to the attributes of largemouth bass, bluegill, and walleye fisheries on order to determine where anglers might choose to fish based on trade-offs in fishing opportunities among these species. 

Principal Investigators: Daniel Isermann and Jonathan Hansen (WDNR)
Graduate Student: Craig Kelling
Our objectives were to determine if: (1) diet overlap and predation occurs between walleye and largemouth bass (2) hatch timing and water temperature influences growth of age-0 largemouth bass (3) the extent of piscivory in age-0 largemouth bass cohorts varies in relation to total length in Wisconsin lakes. 

Principal Investigators: Daniel Isermann, Michael Hansen, Jonathan Hansen (WDNR)
Graduate Student: Kaitlin Schnell
Our objective was to use predictive modeling to determine if largemouth bass abundance, recruitment potential, and size structure in four northern Wisconsin lakes would change in relation to instantaneous fishing mortality rates (F) and changes to harvest regulations. 

Stock Characteristics of Lake Whitefish in Lake Michigan
Principal Investigators: Daniel Isermann, Brian Sloss, Justin VanDeHey, Derek Ogle (Northland College), Scott Hansen (WDNR)
Graduate Student: Matt Belnap
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.

Statewide Evaluation of Calcified Structures Used for Walleye Age Estimation
Principal Investigators: Daniel Isermann, Ryan Koenigs, Ron Bruch, and Connie Isermann
Biologists in Wisconsin and elsewhere use 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. We have collected scales, otoliths, dorsal spines, and anal fin spines from more than 700 walleyes from different locations in the state of Wisconsin. All structures were 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 agreed with sectioned otolith ages, the method considered to be most reliable for estimating the age of walleyes and many other species of fish. An additional sample of fish was collected from a Sturgeon Bay walleye tournament in 2013. We have provided draft walleye sampling protocols to the WDNR Fish Age Task Group that include length-based guidelines for removing dorsal spines in reference to replicating otolith ages. We have also developed a model for “correcting” spine ages based on observed otolith ages at a specified spine age.​

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