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

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 < Δ N e < −1.0). In three trials, a net gain in N e (0.3 < Δ N 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 (Δ N 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.