Muskellunge Management: Fifty Years of Cooperation Among Anglers, Scientists, and Fisheries Biologists

Spatial Genetic Structure of Muskellunge in the Great Lakes Region and the Effects of Supplementation on Genetic Integrity of Remnant Stocks [Extended Abstract]

Keith N. Turnquist, Wesley A. Larson, John M. Farrell, Patrick A. Hanchin, Kevin L. Kapuscinski, Loren M. Miller, Kim Scribner, Chris C. Wilson, and Brian L. Slosss

doi: https://doi.org/10.47886/9781934874462.ch40

The Muskellunge Esox masquinongy is an ecologically important apex predator that supports numerous recreational fisheries throughout their range. Several strains of Muskellunge exist in the Great Lakes region, including Great Lakes Muskellunge native to the five Great Lakes and the St. Lawrence River and northern Muskellunge native to tributaries of the Mississippi River and other inland waters (Becker 1983). Unfortunately, declines in Muskellunge abundance from overharvest and environmental degradation have threatened the viability of many populations and prompted restoration efforts that often include stocking. However, Muskellunge were commonly stocked without an understanding of existing spatial genetic structure, potentially subjecting native populations to admixture and the negative effects of outbreeding depression. The goal of our study was to investigate spatial population structure and genetic diversity in 42 populations of Muskellunge sampled across Great Lakes spawning aggregates, Great Lakes tributaries, and adjacent inland populations to inform future management and supplementation practices.

We genotyped 1,896 Muskellunge (N = 10–123/population) at 13 microsatellite loci developed by Sloss et al. (2008) to assess genetic diversity within and across 42 populations (Figure 1). To assess population structure, we calculated F-statistics to measure the genetic difference between populations, created a neighbor joining tree using Nei’s genetic distance (DA), conducted multiple analyses in the program STRUCTURE (Pritchard et al. 2000) to identify different genetic groups, and investigated patterns of isolation by distance.

Genetic diversity measures varied substantially among populations, and the variation between populations did not appear to be associated with geographic proximity. For example, the two populations with the lowest allelic richness and heterozygosity were nearly 700 km apart. However, populations from one geographic region, inland Michigan, displayed higher than average diversity indices due to admixture (see below).

Analyses of spatial genetic structure revealed that the largest genetic differences were between populations of Great Lakes origin and populations of northern (inland) origin (overall FST = 0.23; Figure 2). Significant population differentiation also existed within each group (Great Lakes FST = 0.15; northern (inland) FST = 0.16; Figure 2). Genetic structure was generally correlated with geography; however, there was only marginal evidence of isolation by distance, likely due to high genetic differentiation among proximate populations.