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We sought to determine whether electrofishing catchability was density dependent and varied with physical and biological factors for walleyes Sander vitreus, largemouth bass Micropterus salmoides, smallmouth bass M. dolomieu, northern pike Esox lucius, and muskellunge E. masquinongy in Wisconsin lakes. Electrofishing catch rate (number of fish caught per shoreline mile) was linearly related to population density (number of fish per acre) in spring for largemouth bass, northern pike, and muskellunge and in fall for walleyes, largemouth bass, and smallmouth bass. In contrast, gear saturation caused the electrofishing catch rate to be nonlinearly related (hyperstable) to population density for walleyes and smallmouth bass during spring. Catchability was higher during spring than fall for walleyes, largemouth bass, and smallmouth bass. Catchability of walleyes during fall was positively related to the percentage of littoral zone, whereas catchability of largemouth bass, smallmouth bass, and muskellunge was negatively related to the shoreline development index. Other physical and chemical variables failed to describe significant residual variation in catchability of any other species in any other season. We conclude that population density cannot be accurately estimated from the electrofishing catch rates of walleyes and smallmouth bass during spring. Therefore, mark-recapture methods must still be used to estimate population density if managers choose to sample those species during spring in Wisconsin lakes.

a b s t r a c tThe growth of age-0 fishes influences survival, especially in temperate regions where size-dependent over-winter mortality can be substantial. Additional benefits of earlier maturation and greater fecundity may exist for faster growing individuals. This study correlated prey densities, growing-degree days, water-surface elevation, turbidity, and chlorophyll a with age-0 walleye Sander vitreus growth in a southcentral Nebraska irrigation reservoir. Growth of age-0 walleye was variable between 2003 and 2011, with mean lengths ranging from 128 to 231 mm by fall (September 30th-October 15th). A set of a priori candidate models were used to assess the relative support of explanatory variables using Akaike's information criterion (AIC). A temperature model using the growing degree-days metric was the best supported model, describing 65% of the variability in annual mean lengths of age-0 walleye. The second and third best supported models included the variables chlorophyll a (r 2 = 0.49) and larval freshwater drum density (r 2 = 0.45), respectively. There have been mixed results concerning the importance of temperature effects on growth of age-0 walleye. This study supports the hypothesis that temperature is the most important predictor of age-0 walleye growth near the southwestern limits of its natural range.

Stream fragmentation can be detrimental to lotic fish species by preventing important life history movements. The maximum swimming speed and jumping ability of 10 stream fish species were evaluated to describe potential water velocity and height barriers to fish movement. A 10-L swim tunnel was used to test maximum swimming performance and an artificial waterfall with an adjustable weir was used to test jumping performance. All tested fish were between 30 and 100 mm total length. Mean maximum swimming velocity ranged from 37.5 § 1.2 cm/s for mosquitofish to 65.0 § 1.7 cm/s for largemouth bass and jumping ability ranged from 0 cm for bluegill to 13 cm for green sunfish. Differences in swimming and jumping ability demonstrate how limits to dispersal can be taxa specific and therefore, impact the conservation of rare species and management of exotic species. The values determined in this study can be useful in creating models to predict barriers to fish passage.

Gender‐ and year‐specific survival (S) of yellow perch Perca flavescens, the tag recovery rate (f, i.e., the joint probability of a fish being harvested, the tag being recognized, and the tag being reported, corrected for tag loss and tagging mortality), and natural mortality (v) were estimated using Brownie tag recovery models. These models were constructed from 4 years of tagging and angler tag recovery data to determine whether mortality is additive or compensatory for the high‐ and low‐quality yellow perch fishery types commonly found in eastern South Dakota glacial lakes. Natural mortality comprised the majority of total annual mortality, S was constant among years, and f was female‐biased for both study populations. Survival and f did not vary among years for the low‐quality population, providing inconclusive evidence of mortality function. However, a constant S coupled with annual changes in f and v (i.e., when harvest mortality increased, natural mortality decreased) suggests that mortality was compensatory for the high‐quality population. Received October 13, 2010; accepted March 3, 2011

Size-selective angler behavior or the implementation of length-based regulations may have implications in harvest-oriented yellow perch (Perca flavescens) fisheries where perch populations may display sexual size dimorphism (SSD), even though the occurrence of SSD remains poorly documented. Predicted and observed mean lengths-at-age were used to describe the occurrence of yellow perch SSD in populations from four states and one Canadian province. In addition, abiotic and biotic variables were used to predict the occurrence of SSD in yellow perch populations. Predicted mean lengths-at-age were significantly greater for female yellow perch after age 3 indicating female-biased SSD (higher female growth rates and greater maximum attainable lengths) occurred upon maturity. Using observed mean lengths-at-age, 85% of the study populations had at least 1 year class where females were significantly larger than males. Femalebiased SSD was present in almost two-thirds of the individual observed mean length-at-age year class comparisons. SSD could not be reliably predicted using yellow perch population dynamics or lake morphometry. Although, yellow perch SSD was positively correlated with lake productivity, a low fit statistic suggests a poor predictive relationship. This study has demonstrated the prevalence of female-biased SSD in yellow perch populations. Because yellow perch anglers are size selective and harvest oriented, the occurrence of female-biased SSD in a perch population will likely result in female-biased exploitation and, therefore, we recommend natural resource agencies collect age and gender-specific data to identify the occurrence of SSD in perch populations.

During certain times of the year high densities of larval fish can impact the aquatic community. The specific role of freshwater drum (Aplodinotus grunniens) is not known but larval freshwater drum can be abundant in some systems and have been shown to feed on zooplankton. To assist with understanding the role larval freshwater drum play in reservoirs, we investigated changes in peak abundance from 2003-2010 in addition to food habits and prey electivity in 2008 in a South Central Nebraska reservoir. We found that larval freshwater drum abundance varied 100-fold during this study. Cladocerans were an important food item for larval freshwater drum. Freshwater drum >10 mm total length selected for Daphnia spp. (46-80 % of organisms found in stomach), while freshwater drum 10 mm total length selected for Bosmina spp. (37% of organisms found in stomach), which is a less common group of zooplankton in this reservoir. All larval freshwater drum showed a negative selectivity for copepod nauplii (the Strauss index value of À0.35 for all length groups). Based on the food habits described in this study, larval freshwater drum have the potential to compete with larval sport fish species for desirable zooplankton (ie, Daphnia spp.).

Cobble substrate for walleye (Sander vitreus) spawning was added at Sherman Reservoir, Nebraska, in January 2008. We evaluated changes in relative adult walleye abundance and egg density in response to the cobble substrate and estimated site fidelity of adult walleye during the spawning seasons of 2007, 2008, and 2009. A 15% increase in electrofishing catch-per-unit-effort (CPUE) of adult walleye was observed on the cobble substrate the first season it was available (2008), but a 5% decrease in electrofishing CPUE was observed the second season (2009) compared to the 2007 season. While gill nets were not run during the first season the cobble was available, a 113% increase in gill net CPUE was observed the second season. During the first season the cobble was available, a 215% increase in egg density was observed, but no increase in egg density was found in the second season. Site fidelity of adult walleye within a spawning season was 94% and was 81% between seasons. These results indicate that the addition of the cobble substrate increased the relative abundance of adult walleye and density of eggs on the cobble substrate.