USING AN INDIVIDUAL-BASED MODEL TO PREDICT THE GENETIC IMPACTS OF STOCK ENHANCEMENT OF RED DRUM IN SOUTH CAROLINA.

Stock enhancement, the deliberate release of aquaculture-produced animals to augment important recreational and commercial species, provides an appealing alternative to restrictive fishing regulations, but is often criticized for its potential to cause decreased genetic diversity in the enhanced wild population. Individual-based models (IBMs), due to their inherent flexibility in user-input, are effective tools in predicting the genetic impacts of stocking a priori to avoid irreversible declines in genetic diversity that may result from indiscriminate releases of cultured fish. This study explored the use of an IBM to predict the genetic impacts of stocking juvenile red drum Sciaenops ocellatus, a long-lived species (~40 yrs) with overlapping generations, on the spatially separate offshore adult population in SC. The model was built using the R program "rmetasim," parameterized using pre-existing demographic and microsatellite data, and validated using empirical estimates of genetic diversity to mimic the natural population. I ran a total of 48 simulations, 50 replicates each, examining different stocking designs: i.e. stocking period (15, 30 and 45 years), number of wild-caught parents (2, 6, 10 and 20) used in spawning tanks, but rotated out of production every year, and the proportion (10, 30, 50 and 90%) of stocked fish from each year-class that survive and contribute to the wild population. A suite of genetic diversity metrics (raw allele count, allele size range, effective number of alleles, observed heterozygosity (H_O), expected heterozygosity (H_E), the inbreeding coefficient (F_IS), effective number of breeders per year-class (N_b), and the effective population size (N_e) of the mixed-age (5-40 yrs) adult population) were calculated after an initial 100-year model burn in period, each year that stocking occurred, and every 10 years post-stocking during a 50-year population recovery period (N=1000 at each time point). Results show that after a 15-year stocking period (1 generation length for red drum), the negative genetic impacts caused by greater contributions of cultured fish in the wild can be mitigated by increasing the number of parents used in spawning tanks (Table 1). The following recommendations should be applied to the red drum stock enhancement program in SC in order to effectively enhance the sub-adult population while minimizing negative genetic impacts: stocking can occur every year for 15 years and year-class contributions of cultured fish in the sub-adult population can reach proportions as high as 10, 30, 50 and 90% as long as the total number of wild-caught parents used in spawning tanks corresponds to 2, 6, 10 and 20, respectively, and the population health is reassessed during a recovery period prior to continuation of the enhancement program.