Walleye Density Research Articles

Food web alterations that promote native species: the recovery of cisco (Coregonus artedi) populations through management of native piscivores

We evaluated the effects of fisheries management on food webs in three northern Wisconsin lakes with exotic rainbow smelt (Osmerus mordax). In two of the lakes, restrictions on fishing reduced mortality rates on adult walleye (Sander vitreus) during the study period. In these lakes, walleye populations increased concurrently with a decline in rainbow smelt populations. As rainbow smelt populations declined in both lakes, native cisco (Coregonus artedi) populations increased. Our analysis of walleye diets illustrated that walleye fed selectively on rainbow smelt but did not feed on cisco during the summer months. When entered into bioenergetics simulations, this information demonstrates that walleye predation alone was enough to cause the observed rainbow smelt declines in our study lakes. Our results indicate that increased walleye density allows for a parallel increase in cisco density. Based on our results, fishery regulations to restore walleye to high densities in lakes invaded by rainbow smelt may restore native planktivores that have co-evolved traits.

Can growth be used as a surrogate measure of walleye (Sander vitreus) abundance change?

We examined several models to determine the relative contributions of density-dependent and density-independent factors on walleye (Sander vitreus) growth in the ceded territory of Wisconsin from 1990 to 1999. We then used independent data from 2000 to determine how well each model predicted walleye growth and examined several models to determine if growth could be used to predict density. Adult density best predicted the mean size of age-3 males ( [Formula: see text]3m) and age-5 females ( [Formula: see text]5f). Density-independent measures of pH, the morphoedaphic index, maximum depth, and conductance had a positive influence on growth, while adult density negatively affected growth. The solely density-dependent models predicted [Formula: see text]3m and [Formula: see text]5f poorly in 2000. The addition of density-independent factors improved model predictions of [Formula: see text]3m and [Formula: see text]5f. Walleye growth did not predict adult walleye densities. Regional patterns in walleye growth were correlated with surrogate measures of lake productivity and to a lesser extent adult density. Density dependence had a relatively weak affect on growth patterns, suggesting that growth cannot be used as a surrogate method for monitoring abundance change.

Spatial Patterns Emphasize the Importance of Coastal Zones as Nursery Areas for Larval Walleye in Western Lake Erie

Lake Erie walleye Sander vitreus exhibits significant interannual variability in year-class strength. Recent research revealed the importance of larval growth and survival rates in determining walleye year-class strength in western Lake Erie, indicating that spatial and temporal overlap of larvae with good habitat conditions (e.g., abundant prey, warm waters) promoted walleye growth and survival. To assess the spatial overlap between walleye larvae and habitat parameters (water depth, temperature, water clarity, prey density) in western Lake Erie, we evaluated the spatial distribution of walleye larvae and these habitat parameters with intensive sampling at 30 to 36 sites during spring 1994–1999. We analyzed spatial relationships among pelagic walleye larvae and various habitat attributes using a geographic information system and principal components analysis. Larval walleye density was consistently highest at nearshore sites during all years and showed a high degree of spatial overlap with high ichthyoplankton density, and warm water temperatures. Larval walleye density was negatively associated with water depth and water clarity. Two principal components represented 79.6% of the total variability in site attributes. Principle components analysis supported our spatial analysis by graphically separating sites into distinct groups based on larval walleye density and habitat attributes. These analyses indicated that similar relationships between larval distribution and habitat attributes occur each year, emphasizing the importance of nearshore coastal zones as nursery areas for walleye.

Consumption Dynamics of the Adult Piscivorous Fish Community in Spirit Lake, Iowa

AbstractAt Spirit Lake, one of Iowa's most important fisheries, walleye Sander vitreus (formerly Stizostedion vitreum) is one of the most popular species with anglers. Despite a century of walleye stocking and management in Spirit Lake, walleye growth rate, size structure, and angler harvest continue to decline. Our purpose was to determine the magnitude and dynamics of walleye population consumption relative to those of other piscivorous species in Spirit Lake, which would allow managers to judge the feasibility of increasing the abundance, growth rate, and size structure of the walleye population. We quantified food consumption by the adult piscivorous fish community in Spirit Lake over a 3‐year period. Data on population dynamics, diet, energy density, and water temperature from 1995 to 1997 were used in bioenergetics models to estimate total consumption by walleye, yellow perch Perca flavescens, smallmouth bass Micropterus dolomieu, largemouth bass Micropterus salmoides, black crappie Pomoxis nigromaculatus, and northern pike Esox lucius. Estimated annual consumption by the piscivorous community varied roughly fourfold, ranging from 154,752 kg in 1995 to 662,776 kg in 1997. Walleyes dominated total consumption, accounting for 68, 73, and 90% (1995–1997, respectively) of total food consumption. Walleyes were also the dominant consumers of fish, accounting for 76, 86, and 97% of piscivorous consumption; yellow perch followed, accounting for 16% of piscivorous consumption in 1995 and 12% in 1996. Yellow perch were the predominant fish prey species in all 3 years, accounting for 68, 52, and 36% of the total prey consumed. Natural reproduction is weak, so high walleye densities are maintained by intensive stocking. Walleye stocking drives piscivorous consumption in Spirit Lake, and yearly variation in the cannibalism of stocked walleye fry may be an important determinant of walleye year‐class strength and angler success. Reducing walleye stocking intensity, varying stocking intensity from year to year, and attempting to match stocking intensity with the abundance of prey species other than walleye may improve the walleye fishery in Spirit Lake.

A Reexamination of the Relationship between Electrofishing Catch Rate and Age‐0 Walleye Density in Northern Wisconsin Lakes

AbstractWe quantified the relationship between the population density (number/acre) of age‐0 walleyes Sander vitreus (formerly Stizostedion vitreum) and electrofishing catch per effort (CPE; number/mi) in 19 Wisconsin lakes to update a 1982 analysis by Serns, who used linear regression through the origin to develop a model from a small data set that has been widely used to estimate age‐0 walleye density from electrofishing CPE. We added new data, explicitly tested for the linearity of the relationship, and accounted for the effect of measurement errors. We found that electrofishing CPE was nonlinearly related to the population density of age‐0 walleyes, which indicated that the catchability of age‐0 walleyes to electrofishing declined with population density. The measurement errors in electrofishing CPE were more than nine times as great as those in age‐0 walleye population density, so that the parameters of the relationship between electrofishing CPE and age‐0 walleye density were accurately estimated by ordinary‐least‐squares linear regression. Among lakes, the variation in the catchability of age‐0 walleyes to electrofishing was positively related to the variation in specific conductivity but not to the variation in other physical features (shoreline complexity or littoral area) or chemical features (alkalinity or pH). Within lakes, the variation in the catchability of age‐0 walleyes to electrofishing was negatively related to the variation in temperature at the time of sampling. We recommend that electrofishing CPE only be used as a crude index of age‐0 walleye population density.

Catchability of Walleyes to Fyke Netting and Electrofishing in Northern Wisconsin Lakes

Abstract We quantified relationships between both fyke-net catch rates (catch/net-night) and electrofishing catch rates (catch/mi) and population densities (number/acre) of walleye Sander vitreus (formerly Stizostedion vitreum) for adult population estimates and total population estimates to determine whether catchability was density dependent. Fyke-net catch rates were modeled as a nonlinear function of adult walleye density and of four size-classes of the adult population, and electrofishing catch rates were modeled as a nonlinear function of adult and total walleye density and four size-classes of the adult and total populations. The results showed nonlinear relationships between catch rate and density for the adult and total populations. We accounted for measurement errors in catch rates and densities by estimating bias-corrected slopes by means of Monte Carlo simulations and estimated measurement-error ratios by means of an errors-in-variables model. We found that the bias-corrected slopes were highe...

Impacts of Daily Bag Limit Reductions on Angler Effort in Wisconsin Walleye Lakes

Angler effort is an important factor affecting recreational fisheries. However, angler responses are rarely incorporated into recreational fisheries regulations or predictions. Few have attempted to examine how daily bag limit regulations affect total angling pressure and subsequent stock densities. Our paper develops a theoretical basis for predicting angler effort and harvest rate based on stock densities and bag limit regulations. We examined data from a management system that controls the total exploitation of walleyes Sander vitreus (formerly Stizostedion vitreum) in northern Wisconsin lakes and compared these empirical results with the predictions from a theoretical effort and harvest rate response model. The data indicated that higher general angler effort occurs on lakes regulated with a 5-walleye daily limit than on lakes regulated with either a 2- or 3-walleye daily limit. General walleye catch rates were lower on lakes with a 5-walleye limit than on lakes with either a 2- or 3-walleye daily limit. An effort response model predicted a logarithmic relationship between angler effort and adult walleye density and that an index of attractiveness would be greater on lakes with high bag limits. Predictions from the harvest rate model with constant walleye catchability indicated that harvest rates increased nonlinearly with increasing density. When the effort model was fitted to data from northern Wisconsin, we found higher lake attractiveness at 5-walleye-limit lakes. We conclude that different groups of anglers respond differently to bag limit changes and that reliance on daily bag limits may not be sufficient to maintain high walleye densities in some lakes in this region.

Development of a Regional Stock–Recruitment Model for Understanding Factors Affecting Walleye Recruitment in Northern Wisconsin Lakes

Abstract We used data from 162 lakes in northern Wisconsin during 1990–1999 to develop a stock–recruitment model for walleye Stizostedion vitreum and to identify important factors affecting recruitment. We used the linear version of the Ricker stock–recruit model and regression tree analysis to model age-0 walleye density, which ranged from 0.24 to 505 per km of shoreline (mean = 51.2). Adult walleye density ranged from .040 to 5.9 per surface hectare (mean = 1.5). The density of adult (sexually mature) walleyes, calendar year, and angling harvest rate of yellow perch Perca flavescens were significant descriptors of age-0 walleye density. Adult walleye density explained 10% of the variation in age-0 walleye abundance, which exhibited significant compensatory density dependence. Calendar year and yellow perch density explained nearly 32% of the residual variation in age-0 walleye density. The average age-0 walleye density in high-recruitment years (1991, 1994, and 1995) was 74.2/km, whereas the average age...

Prediction of Angler Catch Rates Based on Walleye Population Density

Abstract Management of angler harvest of walleyes Stizostedion vitreum assumes that angling catch rates can be regulated by fish densities. Data on walleye densities in northern Wisconsin lakes obtained between 1990 and 1993 were used to develop a predictive model for walleye angling catch rates. Data collected in 1993–1994 were used to validate these models. Total numbers of walleye per acre were estimated from mark-recapture experiments conducted during April and May of each year. Creel surveys were conducted starting on the first Saturday in May and ending on 1 March of the following year for waters where population estimates were made. Linear regression indicated a high correlation between walleye densities and yearly walleye catch rates (r = 0.92, P < 0.05). Using the linear equation generated from this analysis, we predicted yearly walleye catch rates from walleye population estimates in 11 lakes for 1993–1994. All 11 angler catch rates were within the 95% prediction intervals. When data from 1993–1...

Effects of Prey and Predator Abundances on Prey Consumption and Growth of Walleyes in Western Lake Erie

Declining growth and delayed age at maturity of walleye Stizostedion vitreum from 1965 to 1984 indicated that the speciesˈ large Lake Erie population was taxing the capacity of the prey fish community to support it. We examined the effects of prey and predator abundances on walleye diets and estimated the total predatory demand of age-0 through age-6 walleyes in western Lake Erie during 1986–1988. Walleye diets reflected prey fish abundances. Gizzard shad Dorosoma cepedianum and shiners (emerald shiner Notropis atherinoides and spottail shiner N. hudsonius) were the major prey in years when they were abundant. In years when these prey species – especially gizzard shad – were not abundant, walleyes consumed more white perch Morone americana and (to a lesser degree) yellow perch Perca flavescens. Total consumption by the walleye population was relatively constant, ranging from 83,700 tonnes in 1987 to 94,300 tonnes in 1986. Bioenergetics modeling showed that greater fishing mortality imposed on strong walleye year-classes could reduce competition among older cohorts; however, because diets of age-0 and age-1 walleyes differ from diets of older fish, few prey made available by greater harvests would be used by small walleyes to increase their growth. Walleye density and gizzard shad availability interact to influence prey consumption and walleye growth in western Lake Erie, High predatory demand and reduced growth of walleyes occur when large walleye year-classes predominate.

Effect of Fish Density on Growth, Survival, and Food Consumption by Juvenile Walleyes in Rearing Ponds

Abstract We investigated the effect of density of young-of-year walleyes Stizostedion vitreum on their growth, biomass production, survival, and food consumption. We used 2-d-old larvae stocked at densities of 20, 40, and 60 fish/m3 in eight drainable outdoor ponds (unbalanced design with one additional replicate for high and low densities). Growth, food consumption, and prey density were monitored weekly during the 6-week experiment. Mean length and weight at harvest showed an inverse logarithmic relationship with initial walleye density, whereas biomass production and initial density were positively related. There was no relationship between the within-pond variability in walleye size at harvest and either stocking density, final density, or mean harvest length and weight. The rate of survival was also unrelated to either initial density or size at harvest. Our results support the contention that growth is more important than mortality in adjusting population biomass to environmental conditions. However...

Relationships between Storage Ratio and Population Density, Natural Recruitment, and Stocking Success of Walleye in Kansas Reservoirs

Abstract Population density of walleye Stizostedion vitreum vitreum in Kansas reservoirs appeared to be related to storage ratio, with low storage ratios (high discharges) producing low densities of fish, moderate storage ratios yielding high densities, and high storage ratios having walleye densities slightly lower than occur at moderate discharges. Both natural recruitment and stocking success of walleye appeared to be related to the storage ratio, with little stocking success occurring at reservoirs having mean storage ratios of 1.0 or less. It is not known whether these relationships are cause-and-effect, but storage ratio should be considered when determining priorities for walleye stocking or when modeling walleye population dynamics in flood-control reservoirs.

Influence of Various Factors on Density and Growth of Age-0 Walleyes in Escanaba Lake, Wisconsin, 1958–1980

Abstract In Escanaba Lake, Wisconsin during 1958–1980, significant negative correlations were found between the fall density of age-0 walleyes Stizostedion vitreum and both the standard deviation and coefficient of variation of the May water temperatures. Age-0 walleye density in fall over the 23-year period was not influenced by several other temperature relationships or by wind speed and direction, water level, adult density, or density of previous year classes. The first-year growth of walleyes in Escanaba Lake was positively related to the June and combined May-June water temperatures but was not significantly related to temperatures during May or the July-August and May-August periods.