Document Category: Genetics

Over the past decades, an increasing number of fish species have undergone strong decrease in their abundance due to various human activities. Such activities may prevent the free movement of fish, generates pollution and habitat loss, overfishing and many additional problems. To overcome these demographic declines, numerous stocking programs have been implemented to sustain fish populations worldwide. This is the case of the Muskellunge (Esox masquinongy) in the province of Québec, Canada. The species is renowned for his trophy-size specimens which are highly prized by anglers. However, Muskellunge has undergone strong decline in abundance during the first half of the 20th century in the waters of the St. Lawrence River, especially in the greater Montréal region. Consequently, Muskellunge from Ontario and New York State were used for stocking over 1.5 million of individuals from 1950 to 1997. From 1950 to 1965, eggs initially taken from the Chautauqua Lake (New York State, USA) were transferred to the Lachine government hatchery in Québec where fry were reared before being released into the St. Lawrence River, several of its main tributaries and inland lakes. From 1965 to 1986, adults from Lake Joseph were used as source for stocking. Finally, from 1986 to 1997, eggs from Lake Tremblant were used. Muskellunge populations from Joseph and Tremblant Lakes were originally introduced with fish from the Lake Chautauqua source.

Performance of four muskellunge strains (Mississippi, Shoepack, Court Oreilles and Miinocqua) were evaluated in two Minnesota lakes. Shoepack strain matured earlier and at a smaller size than the Mississippi strain. Although temporal spawning periods tended to overlap, Mississippi strain spawned at significantly higher water temperatures than the Shoepack strain. After six growing seasons the Mississippi strain was longer and heavier than the other strains. Weight-length relationships were significantly different with Shoepack and Wisconsin strains exhibiting a more robust body shape. Ultimate growth potential was greatest for the Mississippi and Court Oreilles strains and least for the Minocqua and Shoepack strains. Mortality rates were similar except for the Shoepack strain which had the highest mortality rate. The superior growth performance of the Mississippi strain suggests that it should be the strain of choice for muskellunge culture in Minnesota.

Conservation and management issues related to genetic diversity and stock structure of native populations of muskellunge (Esox masquinongy) have largely been unexplored. In Lake Huron’s North Channel and Georgian Bay, Muskellunge populations have been impacted by historical commercial fisheries, recreational fisheries, loss of spawning habitat, historical water quality issues, and ecosystem changes. To determine the spatial genetic structure of native Muskellunge in Lake Huron and Georgian Bay, spawning adults were sampled from 10 sites in the North Channel and eastern Georgian Bay. Genotyping with 20 microsatellite DNA loci showed substantial spatial genetic structure, with significant pairwise divergences among spawning sites. Individual- and population-based analyses revealed hierarchical population structuring, with strong patterns of spawning site fidelity and isolation by distance; very low levels of dispersal and gene flow over historical and contemporary timescales were indicated. Estimation of effective population sizes highlighted the limited genetic resources that are present in these localized populations. The present results show that Muskellunge in Lake Huron and Georgian Bay consist of multiple small populations with limited ranges and high site fidelity and should be managed accordingly.

Achievement of management goals to maintain, enhance, or re-establish fish species of management importance in the Great Lakes often relies on hatchery supplementation. Issues may arise when individuals of hatchery origin are super-imposed upon natural stocks, particularly when resident species are naturally in low abundance such as with most Muskellunge (Esox masquinongy) populations. We used 12 microsatellite loci to survey 450 individuals from 13 populations to quantify the contributions of stocked individuals to the current Muskellunge stock structure in Michigan and document evidence of inter-strain hybridization. Genetic differentiation among populations based on variance in allele frequency was moderately high (mean Fst = 0.18), and was largely attributed to stocking history. The major genetic discordance was found among populations inhabiting waters with native Great Lakes and native and introduced Northern Muskellunge strains. We identified five genetic lineages, corresponding to native stocks (one Great Lake and two Northern strains) and two Northern Muskellunge strains obtained from other states and stocked across Michigan. Analyses revealed that the majority of populations sampled were composed of multiple hatchery strains of Northern Muskellunge, including waters connected to the Great Lakes and in waters with remnant native stocks. Admixtures of stocked strains and evidence of inter-strain hybridization were widespread. Collectively, data reveal that hatchery programs have the potential to restructure native fish populations on a statewide basis. Greater attention to current genetic stocks of both donor and recipient populations is advised to ensure that future supplementation efforts do not further erode the integrity of native stocks.

We quantified genetic relationships among Muskellunge Esox masquinongy from 15 locations in the Great Lakes to determine the extent and distribution of measurable population structure and to identify appropriate spatial scales for fishery management and genetic conservation. We hypothesized that Muskellunge from each area represented genetically distinct populations, which would be evident from analyses of genotype data. A total of 691 Muskellunge were sampled (n = 10–127/site) and genetic data were collected at 13 microsatellite loci. Results from a suite of analyses (including pairwise genetic differentiation, Bayesian admixture prediction, analysis of molecular variance, and tests of isolation by distance) indicated the presence of nine distinct genetic groups, including two that were approximately 50 km apart. Geographic proximity and low habitat complexity seemed to facilitate genetic similarity among areas, whereas Muskellunge from areas of greater habitat heterogeneity exhibited high differentiation. Muskellunge from most areas contained private alleles, and mean within-area genetic variation was similar to that reported for other freshwater fishes. Management programs aimed at conserving the broader diversity and long-term sustainability of Muskellunge could benefit by considering the genetically distinct groups as independent fisheries, and individual spawning and nursery habitats could subsequently be protected to conserve the evolutionary potential of Muskellunge.