Bullheads Ameiurus spp. are found throughout much of the United States and are infrequently studied species. Although limited information has been published on the Black Bullhead A. melas and Yellow Bullhead A. natalis, it has been shown that bullheads can dominate the fish biomass in some north temperate U.S. lakes, resulting in a fish community exclusive of Walleye Sander vitreus and Yellow Perch Perca flavescens. Recently, recruitment and abundances of popular coolwater sport fishes, such as Walleye and Yellow Perch, have been declining in some northern Wisconsin lakes. These observed declines, coupled with high bullhead densities, led fisheries biologists to conduct whole‐lake bullhead removals on four northern Wisconsin lakes. Removal of Black and Yellow bullheads from these lakes resulted in substantial changes in the fish communities. The CPUE of naturally reproduced age‐0 Walleye increased in Lake Metonga and Patten Lake following the removal of bullheads. Additionally, survival of stocked Walleye increased in Crane and Pickerel lakes after bullhead removals, resulting in higher CPUE of age‐0 and age‐1 Walleye. Subsequently, adult Walleye abundance has increased or remained steady in all bullhead removal lakes. Significant declines in abundance of Bluegill Lepomis macrochirus and increases in abundance of Yellow Perch and Black Crappie Pomoxis nigromaculatus were also observed after bullhead removals, further illustrating a shift in fish community composition. Our observations suggest that when at high densities, bullheads can play a significant role in structuring fish communities and the removal of bullheads can increase recruitment, survival, and abundance of sport fishes like Walleye and Yellow Perch.

When estimating fish population abundance, it is important to recognize that differing habitat use may cause one gear type to be more effective and less biased than another. We generated and compared population abundance estimates (PE) for adult Yellow Perch Perca flavescens in Crystal Lake, Wisconsin using a spring mini‐fyke net mark–recapture survey and summer hydroacoustic surveys. Mean PE from the spring mark–recapture survey was 11,051 adult Yellow Perch (95% confidence limits of 9,878 and 12,541). This mean was 4.0–8.5 times greater than the range of mean summer hydroacoustic estimates (mean ± 95% CI = 1,291 ± 312 and 2,912 ± 703). Due to Yellow Perch spawning behavior, we assumed that the spring mark–recapture survey sampled the entire adult population, while summer hydroacoustics sampled the postspawn pelagic component. Using the mean of all hydroacoustic surveys (PE = 2,492; n = 5), we estimated that approximately 22% of adult Yellow Perch selected for pelagic habitats postspawn. Our study emphasizes the importance of evaluating gear bias and has implications for future assessments, particularly when the target species may exhibit multiple habitat preferences within a lake.

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Knowledge of density-dependent responses of fish populations to exploitation is important for the sustainable management of fisheries and in structuring fish populations to meet angler desires. To better understand the densitydependent responses of Walleye Sander vitreus to exploitation, we conducted a 10-year, 50% annual exploitation experiment on Sherman Lake, Wisconsin, during 2007-2016. In the following order, annual exploitation goals were met through liberalized recreational angling regulations, tribal spearfishing, and physical removals (if necessary). Response variables included total and sex-specific adult density, age-0 and age-1 relative abundance, age-0 to age-1 survival, length at maturity, individual growth, and population size structure. To control for environmental and interannual influences on adult density and recruitment, unexploited Escanaba Lake, Wisconsin, was used as a reference system. Total and sex-specific adult density and age-0 relative abundance did not differ between Sherman and Escanaba lakes. Age-1 relative abundance was significantly higher and more variable under elevated exploitation compared with the reference lake. Age-0 to age-1 survival significantly increased between pretreatment and elevated-exploitation time periods. Sex-specific length at maturity significantly declined between pretreatment and elevated-exploitation time periods. Mean juvenile length at age increased, male asymptotic length declined, and the proportional size distribution of quality-sized Walleye declined between pretreatment and elevated-exploitation time periods. Our results suggest that compensatory age-0 to age-1 survival and declines in length at maturity interacted to offset elevatedexploitation effects on adult density. Likewise, density-dependent growth responses were most evident in juveniles. Although the Sherman Lake Walleye population appeared resilient to elevated exploitation, we caution that this level of long-term exploitation is likely not sustainable for most Walleye populations due to the findings of previous exploitation studies and observations of depensatory recruitment dynamics in Walleye.

Black bullheads Ameiurus melas are an environmentally tolerant omnivorous fish species that are found throughout much of North America and parts of Europe. Despite their prevalence, black bullheads are an infrequently studied species making their biology, ecology, and life history poorly understood. Although limited information has been published on black bullheads, evidence suggests that bullheads can dominate the fish biomass and have profound influences on the fish community in some north temperate USA lakes. The goal of our study was to provide additional information on black bullhead population demographics, growth rates, life history characteristics, and seasonal diet preferences in a northern Wisconsin lake. Using common fish collection gears (fyke netting, electrofishing), fish aging protocols, fecundity assessments, and diet indices, our results suggested that black bullheads exhibited relatively fast growth rates, early ages at maturity, moderate fecundity, and a diverse omnivorous diet. Due to these demographic and life history characteristics, black bullheads have the potential to dominate fish community biomass in their native and introduced range. Results from our study may inform the management of black bullhead as native and invasive species.