Contingents of Southern Flounder from Subtropical Estuaries Revealed by Otolith Chemistry

Abstract

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

FUNDING

We thank C. Faulk, J. Kaiser, R. Lopez, and D. Sjostrom (UTMSI) for advice and assistance in fish rearing and collection, and A. Montalvo (UTMSI) for extensive help with fieldwork and sample preparation. Laser ablation and solution measurements were performed at the University of Texas Jackson School of Geosciences, with the assistance of N. Miller. We sincerely thank two anonymous reviewers for suggestions that significantly improved the manuscript. Funding for this research was provided by a grant from Texas Sea Grant to B.D.W.; M.K.N. was also supported by a University of Texas at Austin Graduate School Continuing Bruton Fellowship, a National Science Foundation GK12 Fellowship, and the Allen Jacoby Memorial Scholarship from the Coastal Conservation Association of Texas.