Chapter 2: Genetic Management of North American Paddlefish: Case Studies and Recommendations
Michael R. Schwemm, Allison M. Asher, Edward J. Heist, Thomas F. Turner, and Anthony A. Echelle
Abstract.—Long-term sustainability of the Paddlefish Polyodon spathula will require effective consideration and application of genetic principles and tools by fisheries managers. Paddlefish migration patterns, harvest, and fish culture and stocking for mitigation collectively influence stock structure and genetic resources. Studies since the early 1980s have indicated that Paddlefish showed higher levels of genetic diversity and gene flow in open rivers, but that diversity and gene flow have typically been reduced within geographically isolated and impounded reaches, a result consistent with reduced migratory behavior, river fragmentation, and demographic bottlenecks. Concurrent hatchery propagation methods and broodstock selection probably also contributed to unintentional genetic changes in stocked Paddlefish populations (Gavins Point, South Dakota-Nebraska). We present case studies depicting how stocking has altered the genetic structure of populations and reduced within-population diversity. Documented genetic changes have resulted from 1) annual stocking and low natural reproduction leading to a low effective population size (Table Rock Lake, Missouri), 2) introgression by hatchery-reared broodstock from a distant source population (Gavins Point, South Dakota-Nebraska into Kaw Lake, Oklahoma), and 3) subsampling of genetic diversity in a stocked population (Oologah Lake, Verdigris River, Oklahoma) relative to the broodstock source (Grand Lake, Grand/Neosho River, Oklahoma). We present two other case studies of population genetics issues from Grand Lake, the first suggesting a population bottleneck due to impoundment by dam approximately 80 years ago, and the second detailing the potential genetic effects of episodic recruitment on genetic effective size. Paddlefish in some areas have fortunately retained genetic variation and avoided immediate concerns of inbreeding, due in part to life-history attributes and prudent management. Increased consideration of genetic structure both within states and across jurisdictional boundaries will additionally improve range-wide management decisions. These case studies offer several general conclusions useful to guide future management of Paddlefish populations in order to maintain evolutionary potential and local adaptation, important considerations for conservation and sustainable harvest in modified river systems.