Retention of Three Types of Tags Applied to Adult Red Drum (Sciaenops ocellatus)
Denson, Michael R.
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Tag loss is a vital component of survival estimates that are applied to abundance calculations as part of stock assessments. This study evaluated the retention and reliability of tags used on adult red drum in South Carolina waters. Sampling was conducted by the South Carolina Department of Natural Resources (SCDNR). Between 2001 and 2008, adult red drum (n=1986) were captured as part of an adult monitoring survey in South Carolina, using a bottom longline. Fish were measured, tagged with two external dart tags, implanted with an internal passive integrated transponder (PIT) tag, and fin-clipped for microsatellite genotyping. The retention of the nylon dart, the stainless steel dart, and the PIT tag were evaluated over an eight-year period. External tag retention was estimated using logistic regression and Bayesian analysis, and compared to a subsample of fish held in controlled saltwater recirculating tanks. Microsatellite matches were evaluated for use as accurate individual identifiers, or genetic tags, by using allele frequencies to calculate genotype match probabilities. PIT tag loss was detected by using matching microsatellite DNA genotypes to compare against PIT tag field records. Microsatellites reliably identified individual fish. With as few as five complete and matching loci the match probability was 6.36E-6. PIT tags had 100% retention throughout this study, and were retained for 2048 days in the wild. External tag retention in wild fish decreased significantly over time. Nylon dart tags were retained for approximately one year longer than stainless steel dart tags, and the two had significantly different retention over time at the 90% confidence level. Tag retention in tank-held fish did not vary significantly over time. Nylon dart tags were retained significantly longer in tank-held fish than in wild fish. This was the most complete tag retention study conducted on adult red drum along the coast of the Southeastern United States.