Genetic impacts of shrimp trawling on red snapper (Lutjanus campechanus) in the northern Gulf of Mexico

Genetic variation and genetic relatedness are investigated among age-0 red snapper (Lutjanus campechanus) sampled as bycatch in shrimp trawls from five localities in the northern Gulf of Mexico. Reference samples from the same geographic areas were obtained by sampling a few juveniles at a time during multiple trawl tows. No significant differences in allelic richness, gene diversity, or allele (or genotype) distributions at 16 nuclear-encoded microsatellites were found between the five bycatch samples and reference samples taken from the same geographic area. These results indicate that red snappers taken as bycatch neither have reduced genetic variation relative to the local population nor do they appear to represent a non-random sample from the local population in terms of allele or genotype distributions. Estimates of the within-sample variance of pairwise relatedness did not differ significantly from zero for any bycatch or reference sample. Hence, red snapper in the by- catch samples are not more closely related genetically to one another than would be ex- pected when sampling individuals at random from the local population. These results indicate that there are no direct, detectable genetic impacts of shrimp trawling on red snap- per at the localities sampled.