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
Largemouth 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
Largemouth 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
Lake 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
Biologists 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)
Overharvest 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 EnergiesWilderness 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
(provide link to PDF here).
Black crappie Pomoxis nigromaculatus and yellow perch Perca flavescens support popular, harvestoriented 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) speciesspecific 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 203mm 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.