Evaluating Effects of Exploitation on Annual Apparent Mortality Rates of Paddlefish Using Mark–Recapture Data

Abstract

Knowledge of the effects of exploitation on population dynamics is critical to effective conservation and management of fish populations. To improve our understanding of the effects of sport fishery exploitation on populations of Paddlefish Polyodon spathula, we tested eight additive and compensatory harvest mortality hypotheses for the Paddlefish population in Lake Francis Case (LFC), South Dakota, with 33 years of tag recovery data using dead recovery models in Program MARK. We evaluated additive and compensatory harvest mortality hypotheses by modeling the effects of sport fishery closures on annual apparent survival and tag recovery rates. Our most-supported hypotheses indicated that exploitation prior to the functional closure of the sport fishery (i.e., when exploitation became negligible) was an additive source of mortality. Annual apparent mortality estimates (i.e., 1 − annual apparent survival) of our most-supported model decreased from 0.237 (SE = 0.036) to 0.110 (SE = 0.063) following the functional closure of the sport fishery and coincided with a decrease in recovery rate from 0.095 (SE = 0.015) to 0.010 (SE = 0.004). These results suggest that relatively unregulated sport fishery exploitation can substantially increase mortality rates of Paddlefish populations. The effects of exploitation on mortality likely differ between populations and temporally within populations due to differences in density-dependent mortality rates.

Received January 7, 2014; accepted November 19, 2014

ACKNOWLEDGMENTS

We thank the biologists whose previous hard work made this study possible. We also thank M. Pegg, A. Carlson, J. Krause, K. Bertrand, N. Troelstrup, and the South Dakota State University Ecology Discussion Group for providing comments on earlier drafts of this manuscript. Partial funding for this project was provided by the Federal Aid in Sport Fish Restoration program, Project F-15-R, Study 1511, administered through South Dakota Department of Game, Fish and Parks. The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the U.S. Fish and Wildlife Service.