Red Snapper: Ecology and Fisheries in the U.S. Gulf of Mexico

Abstract

<em>Abstract</em>.—Allelic variation at 19 nuclear-encoded microsatellite loci and haplotype variation in a 590 bp protein-coding fragment of mitochondrial (mt)DNA were assayed among Gulf red snapper sampled from four cohorts at each of three offshore localities (12 samples total) in the northern Gulf of Mexico. Significant heterogeneity in allele and genotype distributions among samples was detected at four microsatellites; six of seven ‘significant’ pairwise comparisons between samples revealed the heterogeneity to be temporal rather than spatial. Nested-clade analysis of mtDNA variants indicated different temporal episodes of range expansion and isolation by distance. Estimates of variance effective population size (microsatellites) ranged between ∼1,000 and >75,000 and differed significantly among localities. The differences in variance effective size likely reflect differences in number of individuals successfully reproducing or differences in patterns and intensity of migration. Collectively, these findings are consistent with the hypothesis that red snapper in the northern Gulf occur as a network (or metapopulation) of semi-isolated assemblages that may be demographically independent over the short term, yet over the long term can influence each other’s demographics via gene flow. This type of population structure may be difficult to detect with commonly used, selectively neutral genetic markers.