Assessing Red Drum Juvenile Stocking in a South Carolina Estuary Using Genetic Identification

The South Carolina Department of Natural Resources has been stocking red drum Sciaenops ocellatus since 1988 to evaluate parameters critical to their successful survival and recruitment in South Carolina estuaries. From 1999 to 2002, between 600,000 and 1,000,000 juvenile red drum were stocked each year in two tributaries of Charleston Harbor. The harbor and each tributary were partitioned into three independent strata and randomly sampled monthly for two decades, allowing population trends before, during, and after stocking to be evaluated. Using microsatellite-based parentage analysis, we examined the contribution of stocked age-0 juvenile red drum (15-60 mm total length) to the local population 1 year after release by using fishery-independent sampling. Analysis of these data showed that the highest contributions (88.9%) were close to the stocking site in years with low natural recruitment, whereas in years with high natural recruitment, contributions were lower and stocking was less effective in increasing catch per unit effort. The results of stocking 600,000 small juveniles/year from 1999 to 2001 in one of the study tributaries (Ashley River) indicated that stocked fish did not displace wild fish but had an additive effect on their abundance, supporting the hypothesis that trophic resources are not limiting for postlarval age-0 red drum within Charleston Harbor. The high observed variability in contribution among years of stocking similar-sized red drum suggests that (1) interpretation on a year-class-specific basis is necessary to fully understand the effects of stocking and (2) marine stock enhancement programs would benefit substantially from evaluation in the context of wild annual recruitment patterns.