Nancy A. Nate

Variation in Walleye Abundance with Lake Size and Recruitment Source

Abstract We quantified the relationship between lake size and abundance of walleyes Stizostedion vitreum at two life stages, age 0 and adult, in 172 northern Wisconsin lakes. We also determined if the relationship varied with recruitment source (stocked or natural) in order to evaluate the current system of management. For adult walleyes, as estimated by mark–recapture in spring, abundance was linearly related to lake surface area. Age-0 walleye abundance estimated by fall electrofishing catch was also linearly related to the miles of shoreline surveyed. Lake surface area explained 59% of the variability in adult walleye abundance across lakes ranging in size from 93 to 15,300 acres. Lake surface area explained 61% of the variation in abundance of self-sustaining walleye populations and 65% of stocked populations. Walleye abundance was higher in lakes sustained by natural reproduction than in lakes sustained by stocking. These patterns in abundance based on recruitment source were also apparent at age 0. ...

Effects of Simulated Angling Regulations on Stunting in Bluegill Populations

Abstract Stunting in populations of bluegill Lepomis macrochirus is a major management problem in the upper midwestern United States, Traditionally, stunting has been attributed to a lack of food resources. An alternative theory suggests that stunting may result from harvest of the large parental males that inhibit spawning by smaller males, allowing small males to direct energy to reproduction instead of to growth. We used a population model to simulate restrictions on harvest of large males under various conditions of vulnerability to angling, growth rate, and angler effort. Regulations tested were a daily bag of 5 fish and seasonal bags of 50 fish or 50 fish but only 1 trophy specimen (>180 mm total length); a limit of only 1 trophy fish during the spawning season; and a spawning season closure. Growth and angler effort had the greatest effects on size structure in simulated bluegill populations; high growth and low effort led to notable increases in mean fish length. Tested regulations and male vulner...

Predicting the Occurrence and Success of Walleye Populations from Physical and Biological Features of Northern Wisconsin Lakes

Abstract We developed a linear discriminant function (LDF) using surface area, mean depth, fetch, and three substrate descriptors to discriminate the presence and absence of walleyes Sander vitreus (formerly Stizostedion vitreum) in 120 northern Wisconsin lakes. The resulting LDF correctly classified 90% of walleye lakes and 85% of nonwalleye lakes. For model validation, the model classified 90% of walleye lakes and 93% of nonwalleye lakes in an independent set of 100 randomly selected lakes. In contrast, within walleye lakes, an LDF using the same variables correctly classified only 60% of 30 self-sustaining walleye lakes and 50% of 30 stocked walleye lakes. For model validation, the model classified 30% of self-sustaining walleye lakes and 73% of stocked walleye lakes in an independent set of 40 randomly selected lakes. To further assess the differences between walleye lakes with self-sustaining and stocked populations, the angler catch rates for largemouth bass Micropterus salmoides, smallmouth bass M....

Variation of Adult Walleye Abundance in Relation to Recruitment and Limnological Variables in Northern Wisconsin Lakes

Abstract We quantified the relationship between the abundance of adult walleyes Stizostedion vitreum and limnological descriptors of 166 lakes in northern Wisconsin to better predict population size than was possible with lake surface area alone. Four models described adult walleye abundance from lake surface area for drainage and landlocked lakes with self-sustaining and stocked populations. For self-sustaining walleye populations, lake surface area and watershed area explained 61% of the variation in the number of adult walleyes in drainage lakes, whereas lake surface area and the percentage of sand bottom explained 71% of the variation in the number of adult walleyes in landlocked lakes. For stocked walleye populations, lake surface area, conductivity, and the percentage of muck bottom explained 98% of the variation in the number of adult walleyes in landlocked lakes, whereas lake surface area and maximum depth explained 64% of the variation in the number of adult walleyes in drainage lakes. We conclud...

A method for correcting the relative weight (Wr) index for seasonal patterns in relative condition (Kn) with length as applied to walleye in Wisconsin

Abstract We determined whether the relative weight (W r) model for walleye Sander vitreus was representative of populations in Wisconsin and if relative weight varied with length seasonally. We then developed standard condition (K n) models that correct for seasonal variation in body condition. We compiled data from 54,657 walleyes sampled during 640 surveys of 202 lakes in 30 Wisconsin counties. Weight–length relationships and mean relative weight varied more widely for Wisconsin populations than for North American populations overall. Weight–length relationships and mean relative weight varied significantly among seasons, with the highest slope (lowest intercept) and mean relative weight in spring, lowest slope (highest intercept) and mean relative weight in early summer, and intermediate slopes (and intercepts) and mean relative weights in late summer and autumn. Mean relative weight increased with length in spring, decreased with length in early summer, and did not change with length in late summer, a...

Determining Optimal Stocking Rates Using a Stock-Recruitment Model: An Example Using Walleye in Northern Wisconsin

Abstract We propose that stock–recruitment models can be used to estimate optimal stocking rates. Data to estimate the optimal stocking rates can be obtained in a relatively short amount of time by sampling similar populations over a few years. Whether the goal of stocking is endangered species recovery or supplementation of recreational fisheries, accurately determining the optimal stocking rate is of ecological and financial importance. As an example, we applied this approach using a Ricker stock–recruitment model to walleye Sander vitreus stocking in northern Wisconsin lakes. Using June stocking data and fall age-0 survey data for 39 lakes over a 14-year time period, we found that the stocking rate resulting in the greatest number of age-0 walleyes was 60 age-0 walleyes/ha. Similarly, using June stocking data and fall age-1 survey data in 18 lakes over a 9-year time period we found that the stocking rate resulting in the greatest number of age-1 walleyes was 75 age-0 walleyes/ha. About 16% of the varia...

Evaluating Assumptions of Mark–Recapture Studies for Estimating Angling Exploitation of Walleyes in Northern Wisconsin Lakes

Abstract To test for violations of the assumptions of mark–recapture studies used to estimate angling exploitation rates of walleye Sander vitreus in northern Wisconsin lakes, we estimated the recapture rate (R/C) of walleyes previously marked for each month of the angling year for five length categories: all lengths combined, less than 12 in, 12–15 in, 15–20 in, and 20 in or larger. The recapture rate declined significantly during the year for all walleye length-classes combined and for all length-classes except walleyes 12–15 in long. The R/C ratio in May increased with length. We conclude that fin regeneration, which contributed to lack of mark recognition, or higher mortality due to marking, may have reduced the number of marks in the R/C ratio and therefore may have biased estimates of walleye angling exploitation rates.

Temporal Profiles of Walleye Angling Effort, Harvest Rate, and Harvest in Northern Wisconsin Lakes

Abstract In regions where water resources are abundant, broad-scale fisheries management requires quantifying fishery trends on a representative sample of lakes and then using these data to evaluate management actions and assess fishery status. Therefore, we quantified regional fishery profiles of the average number of complete-trip interviews, effort per acre, the number of walleyes Sander vitreus harvested per angler-hour, and the number of walleyes harvested per acre among hours, seasons, and years from 1991 to 2002 in northern Wisconsin lakes. The average number of interviews within days was similar between weekday and weekend day types but differed between open-water and ice-fishing seasons, peaking at midday and late afternoon during open water and midday during ice fishing. The average harvest rate within days was similar between day types and seasons and was highest in the morning and afternoon. The average angler effort during the angling season differed between day types and peaked in July on we...

Relationship between Electrofishing Catch Rate and Adult Trout Abundance in Wisconsin Streams

Abstract The relative quickness and cost effectiveness of single-pass electrofishing samples (catch per effort [CPE]) argues for their use over multiple-pass estimates for enumerating stream fish populations. However, CPE can be an imprecise index of fish abundance and therefore may be less useful than more-precise indices of abundance, such as those obtained from mark–recapture or depletion methods, for assessing trout populations. We evaluated the use of single-pass electrofishing samples (catch/mi) as abundance (number/mi) predictors of adult brook trout Salvelinus fontinalis and brown trout Salmo trutta in Wisconsin streams by quantifying the relationship between electrofishing CPE and adult trout abundance. First, we tested for linearity of the relationship between CPE and adult trout abundance while accounting for measurement error. Next, we explained the residual variability in the relationship using physical and biological attributes of surveyed streams. We found that the relationship between CPE ...

Comparison of Mean Length at Age and Growth Parameters of Bluegills, Largemouth Bass, and Yellow Perch from Length-Stratified Subsamples and Samples in Michigan Lakes

Abstract Estimates of mean length at age and von Bertalanffy growth parameters estimated from mean length at age can be biased if based only on age information collected from length-stratified subsamples. However, historic data are often limited to length-stratified subsample summaries. To evaluate the potential for using historic length-stratified subsamples to compare the average growth of fishes among Michigan lakes, we quantified the subsample bias in estimates of the mean lengths at ages 1–10 and von Bertalanffy growth parameters for bluegills Lepomis macrochirus, largemouth bass Micropterus salmoides, and yellow perch Perca flavescens. In regression analysis of estimates based on subsamples and full samples, only two of nine possible tests indicated significant bias in subsamples relative to samples. The mean lengths at ages 1–10 based on subsamples were not biased. Von Bertalanffy growth parameters indicated no bias for bluegill asymptotic length L ∞, largemouth bass early growth rate ω, and yellow...