Exploring Strategies for Gizzard Shad Removal That Account for Compensatory Density Dependence and Uncertainty

Abstract

Gizzard shad Dorosoma cepedianum have been the target of removal efforts in eastern North American lakes due to their omnivorous feeding, which may increase nutrient cycling and contribute to high phytoplankton abundance. We used a simulation model to evaluate the efficacy of a gizzard shad removal program at the Harris Chain of Lakes (HCL), Florida, by testing the effects of the exploitation rate, gill-net mesh size, and harvest interval on the total population biomass and spawning potential ratio (SPR). The analysis accounted for compensatory density dependence of the gizzard shad population and uncertainty in life history parameters. The reductions in gizzard shad biomass and SPR were less than 50% for the two largest mesh sizes (89 and 102 mm) at realistic annual exploitation rates of 0.6–0.8. However, the use of smaller mesh sizes (51 and 64 mm) produced biomass and SPR reductions that exceeded 75% at comparable harvest rates. Current removal efforts at the HCL, which employ a minimum gill-net mesh size of 102 mm, are unlikely to reduce gizzard shad biomass substantially. However, smaller mesh sizes could result in increased bycatch of economically important black crappies Pomoxis nigromaculatus. Our study sheds light on the importance of using simulation models to forecast the effects of removal efforts on target fish species. The results of such models can be used to inform harvest practices to achieve desired outcomes.

Received May 12, 2011; accepted September 12, 2011

ACKNOWLEDGMENTS

We thank B. Baker, C. Barrientos, G. Binion, A. Bunch, M. Bunch, T. Davis, J. Dotson, C. Enloe, P. Hall, G. Kaufman, P. O’Rouke, N. Siepker, E. Thompson, and A. Watts for assistance with field data collection. W. Johnson, J. Benton, and M. Hale of the Florida Fish and Wildlife Conservation Commission office at Eustis provided invaluable logistical and technical support as well as guidance and discussion regarding project development. The authors are grateful to two anonymous reviewers for helpful comments on drafts of the manuscript. M. Catalano was supported by a University of Florida Alumni Doctoral Fellowship. The research presented here was funded in part by the St. Johns River Water Management District, Palatka, Florida, and the Florida Fish and Wildlife Conservation Commission.