Contingents of Southern Flounder from Subtropical Estuaries Revealed by Otolith Chemistry

The identification of contingents within populations that exhibit distinct migratory behaviors and patterns of habitat use can lead to the understanding of the fitness consequences of individual variability in a population and an increased understanding of population dynamics. This study examines the variation in migratory behavior and habitat use patterns in Southern Flounder Paralichthys lethostigma in the northwestern Gulf of Mexico, whose populations have declined rapidly over the last 25–30 years. The putative life history for this species includes short postsettlement movements into low-salinity habitats, followed by estuarine and marine residency for the remainder of life. However, using otolith Ba:Ca in wild-captured fish, two primary contingents were observed: (1) 54% of fish showed marine–estuarine residency for their entire lifetimes, and (2) 46% showed residence in oligohaline habitats for some portion of their lifetimes. For the second group, oligohaline residence varied widely with life history profiles, having between < 5% up to > 95% of values above the oligohaline threshold. Relationships between the proportion of life spent in oligohaline waters and proxies of growth performance were not significant, indicating no apparent difference in the relative advantage of specific residency patterns. Residence in oligohaline habitats thus appears to be facultative for this population, which may be a local adaptation to interannual drought cycles and variable freshwater inputs in the region. Received August 23, 2013; accepted February 4, 2014