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Oshkosh, WI, United States

Mosel K.J.,University of Wisconsin - Stevens Point | Mosel K.J.,U.S. Fish and Wildlife Service | Isermann D.A.,University of Wisconsin - Stevens Point | Hansen J.F.,Bureau of Fisheries Management
North American Journal of Fisheries Management | Year: 2015

Abstract: Harvest regulations for Black Crappie Pomoxis nigromaculatus and Yellow Perch Perca flavescens in the northern USA and Canada have not been thoroughly evaluated, and specific guidance regarding where minimum length limits (MLLs) might improve these fisheries is lacking. We examined whether: (1) transitioning from an aggregate statewide daily creel limit of 25 panfish to species-specific daily creel limits of <25 fish or implementing statewide MLLs could reduce harvest of Black Crappie and Yellow Perch in Wisconsin by ≥25%, and (2) MLLs would improve yield by ≥10% and mean TL of harvested fish by ≥25 mm in Wisconsin fisheries. Creel surveys indicated that ≥94% of Wisconsin anglers did not harvest a Black Crappie or Yellow Perch, and ≤0.12% of anglers harvested a daily creel limit of 25 fish. Daily creel limits would need to be ≤7 fish/ angler to reduce harvest by ≥25%. Statewide MLLs would need to be ≥229 mm for Black Crappie and ≥203 mm for Yellow Perch to reduce harvest by ≥25%, but predicted responses to MLLs varied among simulated populations. In general, MLLs were not predicted to improve yield, indicating that growth overfishing was not a widespread problem. Minimum length limits could improve mean TL of harvested fish, but increases ≥25 mm were only observed under 254-mm and 279-mm MLLs, and anglers would have to accept predicted reductions in harvest of ≥30% to achieve these improvements. A 229-mm MLL offered a more equitable trade-off between increases in mean TLs of harvested fish (11–21-mm improvements) and reductions in harvest (22–37% reductions). Our modeling provides a framework for managers to make more informed decisions regarding harvest regulations, but more information regarding angler preferences is needed for selecting appropriate management objectives and harvest regulations. © 2015, © American Fisheries Society 2015.

Schueller A.M.,National Oceanic and Atmospheric Administration | Fayram A.H.,Bureau of Fisheries Management | Hansen M.J.,University of Wisconsin - Stevens Point
North American Journal of Fisheries Management | Year: 2012

Understanding the dynamics of angling effort and how fish populations are affected by angler effort is an important and often unappreciated component of fisheries management. Our objective was to determine the extent to which angling-induced mortality limits walleye Sander vitreus population density in northern Wisconsin lakes. We developed a simulation model to evaluate the effects on long-term equilibrium walleye population density caused by effort limitations, density-dependent angling effort, and angling regulations. Equilibrium density was limited by angling effort when effort was held constant but was generally lower when effort was density dependent. Equilibrium density ranged from 3.46 to 21.79 adults/ha when effort was density dependent, similar to the observed median density in lakes sustained by natural reproduction (8.7 adults/ha). Median equilibrium density was 23.3 adults/ha when effort was zero. Equilibrium density was higher when harvest was regulated by a minimum length limit as opposed to no length limit and with no postrelease mortality than with postrelease mortality. Population collapse was more likely and equilibrium density was lower when the population density and effort/ha relationship was strongest. Because the observed relationship between adult walleye population density and effort/ha was weaker, we conclude that open-access walleye fisheries in northern Wisconsin are generally self-regulating. However, populations likely persist at lower population densities than would be expected if angling effort were limited to lower levels than those currently observed. Our results are intuitive; however, they suggest that density increases may be on the order of 100% when effort is severely restricted compared with open-access fisheries with unlimited effort. Other fish species may experience different expected density increases with restricted angler effort depending on a number of factors, but our results suggest that population density changes can be dramatic and that similar modeling exercises may be useful to managers of other fish species if increasing density is of interest. © American Fisheries Society 2012.

Jennings M.J.,Bureau of Science Services | Sloss B.L.,U.S. Geological Survey | Hatzenbeler G.R.,Bureau of Science Services | Kampa J.M.,Bureau of Science Services | And 4 more authors.
Fisheries | Year: 2010

Conservation of genetic resources is a challenging issue for agencies managing popular sport fishes. To address the ongoing potential for genetic risks, we developed a comprehensive set of recommendations to conserve genetic diversity of muskellunge (Esox masquinongy) in Wisconsin, and evaluated the extent to which the recommendations can be implemented. Although some details are specific to Wisconsin's muskellunge propagation program, many of the practical issues affecting implementation are applicable to other species and production systems. We developed guidelines to restrict future brood stock collection operations to lakes with natural reproduction and to develop a set of brood lakes to use on a rotational basis within regional stock boundaries, but implementation will require considering lakes with variable stocking histories. Maintaining an effective population size sufficient to minimize the risk of losing alleles requires limiting brood stock collection to large lakes. Recommendations to better approximate the temporal distribution of spawning in hatchery operations and randomize selection of brood fish are feasible. Guidelines to modify rearing and distribution procedures face some logistic constraints. An evaluation of genetic diversity of hatchery-produced fish during 2008 demonstrated variable success representing genetic variation of the source population. Continued evaluation of hatchery operations will optimize operational efficiency while moving toward genetic conservation goals.

Fayram A.H.,Office of the Great Lakes | Tober Griffin J.D.,Office of the Great Lakes | Wendel J.L.,Bureau of Fisheries Management
Aquatic Ecosystem Health and Management | Year: 2014

Walleye (Sander vitreus) populations in Wisconsin are near the center of their geographical range and support valuable fisheries. The role of seasonal temperature and precipitation in Walleye recruitment was examined using regression tree analysis. Climatological variables were estimated at the 8 km2 scale and Walleye recruitment was estimated based on 298 individual electrofishing surveys. Estimated changes in Walleye recruitment between 1950 and 2006 were examined based on changes in explanatory climatological variables. Spring precipitation and summer maximum temperature were significant predictors of age-0 Walleye density and mean estimated changes in these variables between 1950 and 2006 were used to estimate changes in Walleye recruitment. The model predicted a small overall increase in Walleye recruitment and provides insight into the direct role of climatological variables in Walleye recruitment. However, given the low explanatory power (R2 = 0.103), it is likely that historic climatological changes have had a limited effect on recruitment levels. © 2014 Copyright © 2014 AEHMS.

Koenigs R.P.,Bureau of Fisheries Management | Bruch R.M.,Bureau of Fisheries Management | Stelzer R.S.,University of Wisconsin - Oshkosh | Kamke K.K.,Bureau of Fisheries Management
Fisheries Research | Year: 2015

Although accurate age data are essential when estimating somatic growth and mortality rates required to effectively manage exploited walleye (. Sander vitreus) populations, aging structures have not been validated for age ranges present in most walleye populations. Otoliths and dorsal spines were collected from 302 walleye considered known age in the Winnebago System, Wisconsin, USA: 142 that were assigned ages via progression of discrete length modes following an individual strong year class (ages 0-3), and 160 (ages 4-10, 12-13, 16, 18) that were initially tagged at lengths small enough to accurately assign age ±1 year (<380. mm) and later recaptured and assigned an age (assigned age at tagging plus number of years at liberty). Paired aging structures were also collected from over 2000 additional walleye sampled during spawning assessments, tournament monitoring, and other surveys to better understand the relationship between spine and otolith age estimates and to compare catch curve residuals from structure and sex-specific catch curves to standard walleye recruitment indices. We found otoliths were accurate for walleye ages 0-10, while dorsal spines yielded relatively accurate age estimates for walleye ages 1-5, but underestimated age of walleye age-6 and older. Age distributions within catch curves constructed from otolith age estimates correlated well with measured year class strength, while age distributions from dorsal spine age estimates correlated poorly. Our results from fish considered known age validate the accuracy of otolith age estimates for walleye up to age-10, with corroborating evidence from catch curves and accurate recruitment indices strongly suggesting that otoliths are valid for all ages of Winnebago System walleye. We recommend the use of otoliths to accurately estimate walleye age, growth, and mortality, and to provide accurate age data for other population analyses. © 2015 Elsevier B.V.

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