The Genetic Legacy of Stocking Muskellunge in a Northern Minnesota Lake

Abstract

The effects of stocked fish on native populations of the same species are poorly understood. During the 1960s-1980s, the Minnesota Department of Natural Resources (MNDNR) stocked muskellunge Esox masquinongy derived from Shoepack Lake in the Hudson Bay drainage of northern Minnesota into Moose Lake in the Upper Mississippi River drainage. In the mid-1980s, the MNDNR recognized that stocked Shoepack Lake-strain fish (hereafter, Shoepack strain) were not attaining large sizes, and sources were switched statewide; subsequently, muskellunge from a Wisconsin hatchery were stocked once into Moose Lake. We used 14 microsatellite DNA markers to estimate the genetic contribution by each source population to muskellunge sampled in four different years from 1981 to 2004, and we evaluated the effects of Shoepackstrain ancestry on fish size. Two samples in the 1980s had mostly fish with a single ancestry; thus, these fish were probably Shoepack-strain fish stocked a few years earlier or native fish. By 2004, when most fish would have been naturally produced in the lake, contributions from all three source populations were detected, including admixed individuals from crosses among all ancestral sources. The estimated ancestry by source was 52% native Moose Lake ancestry, 29% Wisconsin strain, and 19% Shoepack strain, with 24% of the individuals having pure Moose Lake ancestry. Fish without Shoepack-strain ancestry had a greater median length than did those with Shoepack-strain ancestry and had a greater proportion of legal-sized individuals (total length ! 1,016 mm) in the population. In contrast, Moose Lake and Wisconsin-strain descendents were common among all sizes of fish. Management options include doing nothing, accepting that extensive introgression has already occurred, or manipulating the population by either stocking to dilute Shoepackstrain ancestry or genetic screening to purge the population of Shoepack-strain ancestry.

Muskellunge Growth Potential in Northern Wisconsin: Implications for Trophy Management

“…These observed differences in growth potential may be due to genetic and environmental factors. Genetically distinct groups of Muskellunge exist across their native range (Koppelman and Philipp 1986;Kapuscinski et al 2013), and genetic differences among populations may contribute to observed variation in growth across the species' range (Younk and Strand 1992;Margenau and Hanson 1996;Miller et al 2009). For example, Muskellunge descending from Shoepack Lake, Minnesota, were stocked across Minnesota for more than 30 years, and the genetic legacy of these fish contributed to a paucity of large Muskellunge in Moose Lake, Minnesota (Miller et al 2009).…”

The Impact of Stocking on the Current Ancestry in Twenty Native and Introduced Muskellunge Populations in Minnesota

“…Genotyping.-We genotyped 1,417 muskellunge using the procedures described in Miller et al (2009), except that we discontinued using microsatellite locus EmaA5 so that the remaining 13 loci from Sloss et al (2008) would combine together in a single electrophoresis run. An additional 50-106 repeated reactions per locus were scored to assess genotyping error (sample size was variable because it included positive controls and samples repeated to fill in a few missing genotypes at individual loci).…”

“…Furthermore, genetic markers allow evaluation of reproductive contributions by stocked 1412 MILLER ET AL. fish. Recent advances in genetic techniques and analysis have allowed assessment of stocking even in the absence of baseline samples from the stocking source and recipient populations prior to stocking (Halbisen and Wilson 2009;Miller et al 2009). These genetic tools allow evaluation of the survival and reproductive success of stocked fish from different strains, sometimes many generations after stocking (Piller et al 2005;Finnegan and Stevens 2008).…”

“…The main objectives of this study were to determine the contribution of each strain to the ancestral composition of stocked populations and whether any of the native populations had retained the genetic diversity found in the region prior to stocking. We were particularly interested in the prevalence of ancestry from the slow-growing Shoepack strain because of concerns that it may limit the size attained by Shoepack descendants in stocked populations (Miller et al 2009). We also evaluated factors that may have affected the level of ancestry from stocked strains.…”

Muskellunge Spawning Site Selection in Northern Wisconsin Lakes and a GIS‐Based Predictive Habitat Model

“…Stocking has been attempted to counter some of these losses by supplementing or replacing natural reproduction. However, stocking is expensive (Margenau 1992), can spread or be affected by disease, and influences the genetic composition of individual fish stocks (Miller et al 2009). In the face of increasing human populations and their effects on Muskellunge spawning habitat, the most cost-effective long-term approach may be to preserve natural reproduction.…”