Chapter 1: Paddlefish Life History: Advances and Applications in Design of Harvest Management Regulations
Dennis L. Scarnecchia, Jason D. Schooley, K. Michael Backes, Aaron Slominski, Steven Dalbey, and Youngtaik Lim
Abstract.—In the past decade, advances in our understanding of Paddlefish Polyodon spathula life history have provided additional insight into the information needed for sustainable harvest management of this long-lived species. Recovery of known-age fish in some stocks has enabled stock assessment biologists and managers to not only validate ages of individual fish, but to begin to validate the life histories. A framework for potentially recruited Paddlefish life history can be broken into five stages: 1) immature, 2) maturing, 3) somatic growth and reproduction, 4) prime reproduction, and 5) senescence to death. These stages involve measurable changes in growth in length and weight, gonadosomatic index (GSI), gonadal fat storage (GFBs), reproductive periodicity, natural mortality rates, and, in some cases, fish migrations. Stages 2–5 are typically initiated at younger ages for males than for females. Metabolic demands on Paddlefish result in them progressing through these life history stages more rapidly in southern stocks, inhabiting warmer waters, than in northern ones, inhabiting colder waters. Lifespans in most northerly stocks tend to be 2–3 times longer than for southern stocks. Natural mortality is also typically lower in northern stocks. These differences necessitate fundamentally different harvest management strategies among stocks. Regardless of the stock, however, in the prime reproduction stage, somatic growth is slow or negative, as energy is routed more strongly into reproduction, GSI is at a maximum, the period of gonadal recrudescence (i.e., spawning interval) is minimized, and GFBs are largely or completely depleted in females. Consistent with recommendations for other long-lived freshwater and marine species, harvest management strategies should be specifically planned to retain some older, prime spawning females in the population. In addition, sporadic or episodic recruitment in many stocks makes steady-state harvest models unrealistic, necessitating that harvest be appropriately matched to recruitment rates or events.