Monitoring Changes in Effective Population Size during Pond Culture of Red Drum

Abstract

Reduction of genetic diversity can occur at two general phases in stock enhancement: spawning and pond culture. In the latter case, reduction in genetic diversity can take place if mortality impacts family groups disproportionately during pond culture. The stock enhancement program developed by the Texas Parks and Wildlife for Red Drum Sciaenops ocellatus was used to determine whether this phenomenon occurs with any regularity. Larvae were sampled prior to pond culture to determine the genetic effective size (N_e) of the spawned population. At the end of pond culture, fingerlings were sampled and changes in N_e over the duration of pond culture were measured. In two trials, there was a nominal reduction in N_e during pond culture (−0.9 < ΔN_e < −1.0). In three trials, a net gain in N_e (0.3 < ΔN_e < 0.6) was observed, due to disproportionate mortality that influenced family groups that were overrepresented in larvae samples (prior to pond culture). Significant mortality and family turnover was observed in a single trial, which resulted in a 32% reduction in effective population size over pond culture (ΔN_e = −3.5). These data suggest that changes in genetic diversity during pond culture are variable in magnitude, but are usually minor relative to the impact of variance in spawning success of broodfish.

Received January 7, 2016; accepted August 8, 2016 Published online November 18, 2016

ACKNOWLEDGMENTS

We thank Z. Kirsch, D. Patterson, and M. March for their extensive work in transport of fish from the broodfish facility to the grow-out facility and also for pond culture work. K. Willis and B. Karel provided laboratory assistance. The staff at the Coastal Conservation Association and Central Power and Light Company Marine Development Center, Texas Parks and Wildlife, were responsible for broodfish mariculture and spawning. We especially thank R. Vega and R. Gamez for their oversight in spawning and transport. M. Fisher and D. McDonald provided editorial comments on the first draft of the manuscript. This work was funded in part by a Federal Aid in Sport Fish Restoration Act grant.