A Genetic Assessment of a Red Drum, Sciaenops ocellatus, Stock Enhancement Program

Abstract

The South Carolina Department of Natural Resources began a stock enhancement research program for red drum, Sciaenops ocellatus, as a possible management strategy for augmenting the availability of juveniles for recreational harvest in South Carolina estuaries. Between 1999 and 2011, approximately 6 million juveniles and 260 million larvae were stocked into the Charleston Harbor (CH) estuary, and proportions of stocked fish were found through standardized sampling as high as 49.6% within a subadult year‐class and up to 12% within the spatially separate spawning population. This study evaluated the genetic influences of stocking on the spawning population, using microsatellite loci, and examined any changes in genetic diversity metrics over the course of the stock enhancement program. Percent contribution of stocked fish among subadult and adult collections was compared against measures of genetic diversity. No statistically significant correlations were found among genetic diversity metrics, suggesting that responsible stocking of red drum as small juveniles has not altered the genetic diversity of adults spawning offshore the CH. Life‐history characteristics likely play a large role in mitigating changes in genetic diversity, despite high contributions of stocked fish in some years, because red drum exhibit a long adult life span and benefit from overlapping generations.

Forecasting the genetic influences of red drum stock enhancement in South Carolina

“…Approximately six million juvenile red drum (20–147 mm mean total length) and 260 million larvae were stocked into Charleston Harbor, South Carolina, USA from 1999 to 2011. Contributions of stocked fish were found to be as high as 49.6% to a single year class within the estuary and exhibited an overall contribution of 3.3% to the spawning population offshore (Katalinas et al., ). In addition, tag–recapture data demonstrated that 95% of juveniles were recaptured within 15 km of their initial tagging location (Arnott et al., ), and individuals stocked into the Charleston Harbor estuary exhibited highly localised contributions (2.5%) to the spawning population just offshore with a contribution no >0.3% to neighbouring estuaries (Gerhard, ).…”

“…Red drum are managed as two genetically distinct stocks along the United States’ Atlantic coast, with the stock boundary defined at the North and South Carolina border (SEDAR [Southeast Data Assessment and Review], ).This study followed the more conservative approach of Katalinas et al. () by using stocking data specific to the Charleston Harbor estuary because stocked fish made a greater local contribution to the spawning population offshore, and so any genetic influences of stocking primarily would occur within this region.…”

“…Katalinas et al. () used tag–recapture data specific to the Charleston Harbor estuary and estimated the N C of the local spawning population to be between 4,000 and 350,000 from 2003 to 2011 (the large range likely due to low recapture rates). Due to the large variability and uncertainty in N C estimates, simulations examined values at three orders of magnitude to test the sensitivity of the model to differences in N C and expand its potential application to other stock enhancement strategies.…”

“…Census sizes of 50,000 and 5,000 were chosen because they fall within the range of N C values estimated by Katalinas et al. (), and 500 was chosen to provide an extreme scenario to test the sensitivity of the model. These values serve as a more conservative approach by focusing on the lower range of estimates and provide previously set targets that managers can use when applying the results of this study to neighbouring red drum populations.…”

Economic, ecological and genetic impacts of marine stock enhancement and sea ranching: A systematic review

“…The Texas red drum enhancement programme replaces ~25% of the broodfish with wild each year; nevertheless, the analysis suggested a potential R‐L effect (Gold, Ma, Saillant, Silva, & Vega, ; Karlsson, Saillant, Bumguardner, Vega, & Gold, ). In contrast, no effect on genetic diversity was reported in the stocked red drum population in the South Carolina (Katalinas, Brenkert, Darden, & Denson, ). A series of studies on Japanese red sea bream found a panmictic population in western Japan, but there were differences in allele frequencies in KB (Taniguchi & Sugama, ) and Kochi Bay (Perez‐Enriquez, Takemura, Tabata, & Taniguchi, ) populations, and they suggested that these effects might be caused by hatchery releases.…”