Determining the Efficacy of Wisconsin's Muskellunge Genetic Broodstock Management Plan

Abstract

In 2006, the WDNR Muskellunge Esox masquinongy propagation program underwent a series of strategic modifications aimed at protecting the contemporary genetic integrity of native populations and ensuring the long-term sustainability of Muskellunge in Wisconsin. Changes were made primarily to ensure natural Muskellunge genetic diversity was represented in broodstock. Crossing and rearing strategies were refined to minimize changes in genetic diversity throughout the propagation process to ensure stocked Muskellunge were genetic representatives of the broodstock. To evaluate this goal, two specific criteria were developed. First, the allele frequencies observed within the progeny life stages must match the allele frequencies observed within the broodstock. Second, ≥ 95% of the rare alleles (alleles present in the broodstock at frequencies ≤ 5%) observed within the broodstock must be conserved within the progeny life stages. If the progeny life stages met the two specific criteria (no significant shifts in allele frequencies and ≥ 95% rare allele contribution), genetic integrity was considered maintained and stocked fish were considered genetic representatives of the broodstock. Samples from the 2012 and 2013 production years at Governor Tommy Thompson (GTH) and Art Oehmcke (AOH) State fish hatcheries were genetically analyzed at 14 standardized microsatellite loci. Genetic integrity was inferred by testing for allele frequency differences between broodstock and fry, broodstock and each individual fingerling rearing pond, and broodstock and a pooled fingerling sample (all fingerling rearing pond samples pooled). In 2012, allele frequencies at GTH were similar between broodstock and fry (χ2 = 11.87, df = 28, P = 0.99) and broodstock and pooled fingerlings (χ2 = 8.398, df = 28, P = 1.00). None of the individual fingerling rearing ponds were significantly different than the broodstock (P > 0.05). Conversely, allele frequencies at AOH differed between broodstock and pooled fingerlings (χ2 = 44.58, df = 28, P = 0.02) and between broodstock and four of five rearing ponds (P ≤ 0.01). However, in 2012, ≥ 95% of all rare alleles observed in the broodstock were conserved in the pooled fingerlings at both hatcheries. Similar results were observed in 2013. Allele frequencies were similar between GTH broodstock and the pooled fingerling sample (χ2 = 26.87, df = 28, P = 0.53) and between GTH broodstock and individual rearing ponds (P > 0.05). Allele frequencies within the 2013 AOH production were similar between broodstock and fry (χ2 = 35.34, df = 28, P = 0.16) but differed significantly between broodstock and pooled fingerlings (χ2 = 86.95, df = 28, P ≤ 0.01) and between broodstock and all four rearing ponds (P ≤ 0.01). During 2013, less than 95% of the rare alleles present in the GTH broodstock were conserved in the progeny. Conversely, AOH conserved > 95% of rare alleles in 2013. Overall, the expected genetic results predicted by the prescribed changes to the propagation program were apparent. I am confident my results show major improvements over historical genetic diversity and stability levels. Despite this perceived progress, the current results also identified areas for further improvement. At each hatchery, at least 1 of the 2 specific criteria was met during both years. Differences identified in the spawning/gamete collection protocols between the two hatcheries likely resulted in the majority of the observed results. Specifically, the standardization of the amount of eggs fertilized by each male at GTH and the relatively fewer number of broodfish sampled at AOH. My findings suggest genetic bottlenecks within the propagation program, specifically at AOH, most likely occurred during gamete collection. Stronger adherence to the prescribed broodfish numbers and spawning strategies, specifically the standardization of gametes from each female family group, will improve conservation of genetic diversity among life stages at both hatcheries. The adoption of the gamete collection methods used at GTH by the AOH staff should improve their ability to maintain allele frequencies among life stages. In addition, increasing the number of broodfish sampled at both hatcheries may also increase the chance of rare alleles being conserved. Therefore, stronger adherence to the prescribed broodfish numbers and spawning strategies, will not only reduce the variance in contribution among families, but also increase the conservation of rare alleles. These further refinements will ultimately provide a better representation of the genetic diversity observed within the broodstock during stocking events. Further, the findings of this research have broader implications than just Muskellunge propagation. My results show the importance of ensuring a sufficient number of broodfish are sampled during gamete collection and limiting the variance in gamete contribution among broodfish to maintain genetic integrity within propagation programs. Ultimately, ensuring proper broodstock sampling and gamete collection protocols will aid in the protection of a species’ long term viability.