Charles S. Anderson

Measuring and Correcting for Size Selection in Electrofishing Mark–Recapture Experiments

Abstract In electrofishing, the form of size selectivity is unknown, so parametric models of selection have not been developed. Capture probability can be estimated as a continuous function of fish size for two-sample mark–recapture experiments such as those often made to describe stream fish populations. One approach is based on nonparametric regression by smoothing splines, in which general linear models are fitted to data by penalized maximum-likelihood methods. Capture probabilities modeled this way allow the data to reveal the form of size selectivity and can be used to estimate population size. A confidence band around the estimated capture probability function and confidence intervals for the population estimate are obtained by bootstrapping. A second approach is based on parametric regression models and requires some knowledge of the form of the selection function. A confidence interval for the population estimate is based on the variance estimated by the delta method. These approaches are illustr...

A Review of Trout Management in Southeast Minnesota Streams

Abstract Agricultural development after 1850 in southeast Minnesota degraded instream habitat, and by 1900, the native brook trout Salvelinus fontinalis was extirpated from most streams. By the 1940s, after 60–70 years of stocking, the exotic brown trout Salmo trutta was the most common trout, but abundance was low and limited by lack of reproductive habitat. Soil conservation practices of the 1930s and 1940s and watershed management under Public Law (PL) 566 in the 1950s and 1960s reduced flooding, erosion, and sedimentation and increased infiltration and base flow. By the 1970s, brown trout reproduction was common, but abundance was still low. Fisheries managers of the Minnesota Department of Natural Resources assumed that adult habitat limited abundance, so they improved instream habitat in streams with public access, which increased brown trout abundance in some streams. Experimental management since 1975 has shown that the lack of adult habitat did limit trout abundance. This management regime has al...

Dispersal, Density-Dependent Growth, and Survival of Stocked Steelhead Fry in Lake Superior Tributaries

Abstract When fry of steelhead Oncorhynchus mykiss were stocked at single sites in Lake Superior tributaries during June, fish did not disperse uniformly to fill available habitat. By the end of the growing season, upstream dispersal was minimal and downstream dispersal patterns depended on numbers surviving. When survival was low (1988), density declined linearly for up to 6.5 km downstream. When survival rates were highest (1989), densities appeared to be at carrying capacity for up to 3.5 km below the stocking site; densities farther downstream declined linearly, and the maximum dispersal distance was 10.9 km. Mean weight of young-of-the-year (age-0) fish was density dependent, and overwinter survival was contingent upon the fish achieving a threshold weight. As density of age-0 fish increased (among sites), the density of fish achieving the threshold weight or larger increased to a maximum. Fluctuations in survival between years and streams were probably caused by variable mortality associated with tr...

Optimal Stocking Densities of Walleye Fingerlings in Minnesota Lakes

Abstract A generalized additive model was developed that described the effects of fingerling stocking density on the abundance of walleyes Sander vitreus in 551 lakes in Minnesota. Walleye abundance was measured as a catch per effort (CPE) from 1,511 standard Minnesota Department of Natural Resources gill-net assessments conducted during 1986–2004. In addition to fingerling stocking, the effects of lake morphometry, productivity, and fish community variables on walleye CPE were also described using a generalized additive model. Lake morphometry variables had sharply nonlinear effects on walleye abundance. Walleye abundance declined in lakes with areas less than 1,000 acres and increased rapidly in lakes with depths of less than 30 ft. The lake productivity variable, total alkalinity, was positively related to walleye abundance. Abundance of northern pike Esox lucius had a negative effect and abundance of yellow perch Perca flavescens a positive effect on walleye abundance. The response of walleye abundanc...

Evaluation of Long-Term Retention and Detection of Oxytetracycline Marks in Walleye Otoliths Using Genetic Methodology

Abstract Because neither genetic population assignments nor oxytetracycline (OTC) mark identifications are 100% accurate, genetic methods were modeled alone and in combination with OTC mark observations to identify the source of walleyes Sander vitreus in a supplemented population and to evaluate the accuracy of OTC mark examination in distinguishing stocked fish that had been treated with OTC from those produced naturally in the lake. Readers examined otoliths from 3,663 fish from two year-classes that were sampled up to 5 years after stocking. A subset of 1,578 of the examined individuals were also assigned to source populations based on genotypes at eight microsatellite loci using baseline genetic data from the stocking source and the recipient population (the measure of genetic divergence [F ST] = 0.07 between populations before stocking). The models indicated that OTC mark observation errors occurred in all samples and that the error rates varied among samples and readers. Model estimates of overall ...

Contribution and Performance of Stocked Walleyes in the Recovery of the Red Lakes, Minnesota, Fishery

AbstractOxytetracycline (OTC) marking and genetic assignment techniques were used to evaluate the contribution and performance of Walleye Sander vitreus fry stocked to accelerate the recovery of a recruitment-overfished population in the Red Lakes, Minnesota. Three stockings of OTC-marked fry from an egg source on the Pike River were conducted at densities of 274 to 358 fry/ha to expedite the recovery of the spawning stock in which the adult female biomass had fallen below 0.5 kg/ha for 10 consecutive years. Two additional stockings of OTC-marked fry from an egg source on a Red Lakes tributary were then conducted at 33 and 87 fry/ha to help quantify natural reproduction as the spawning stock recovered. Subsequent inspection of fish from seine and gill-net samples indicated that Pike River fish composed 50% to 94 % of the stocked year-classes and that the stocked year-classes were three of the strongest in the past 25 years. The Pike River fish survived, grew, and matured at rates similar to the native fis...