Recruitment of Stocked Juvenile Red Drum (Sciaenops ocellatus) to the Adult Population in South Carolina
Denson, Michael R.
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Red drum (Sciaenops ocellatus) is a popular food and recreational fishery species along the southeast U.S. and Gulf of Mexico coasts. Although contribution of stocked fish to the wild population in South Carolina has been measured immediately following stocking up to age two, evaluation of stocked fish recruitment to the adult population has not yet been examined and therefore is the focus of this research. Small juveniles (~30 mm TL) were stocked in the Ashley and Wando Rivers of Charleston Harbor in 1999 - 2002 by the South Carolina Department of Natural Resources (SCDNR). Five years after initial stocking (2004 - 2008), adults were sampled via longline nearshore of four major South Carolina estuaries, and tissue samples were collected for genetic analysis. Genotypes of sampled fish were compared to those of broodstock and it was determined that small stocked juveniles do recruit to the adult stock in South Carolina, with a highly localized contribution near Charleston Harbor. Contribution of the identified stocked fish was estimated via several different methods. Contribution to the stocked year classes in particular were estimated by using length data as well as otolith-based age data collected before and during the sampling period. The percentage of the Charleston Harbor adult population identified as stocked fish from three stocked year classes ranged from 5.8% to 66.0% with the most preferred method, using age-length keys, yielding a contribution estimate of 34.9%. Such a high contribution has the potential to cause deleterious genetic and reproductive effects, though the broodstock husbandry and stocking protocol used by SCDNR is designed to minimalize these effects. Additionally, contribution of this magnitude might allow stocked fish to be used as biomarkers to gain a better understanding of the basic population parameters of adults in South Carolina for management.