PS 22-104 - The use of stable isotopes and trace element analysis to investigate freshwater residency patterns of southern flounder (Paralichthys lethostigma) in South Texas

Tuesday, August 9, 2011
Exhibit Hall 3, Austin Convention Center
Megan K. Nims, Marine Science Institute, The University of Texas at Austin, Port Aransas, TX and Benjamin Walther, The University of Texas at Austin

Previous research conducted in the Northern Gulf of Mexico and North Carolina, has shown that southern flounder (Paralichthys lethostigma) exhibit significant freshwater residency patterns during the juvenile life stage. Juvenile southern flounder have been collected at salinities below 10 ppt in Aransas Bay, suggesting that Texas southern flounder might also have critical periods of freshwater residency. However, the presence of a freshwater residency period in southern flounder in Texas has not previously been tested. Freshwater residency patterns will be determined using otolith microchemistry, analyzing for stable isotopes (87Sr/86Sr) and trace element (Sr:Ca, Ba:Ca) ratios. Otoliths will also be used to establish age, hatch date, and growth rate of southern flounder, in order to investigate if the presence of a freshwater residency period results in differential growth rates, condition, or recruitment into the fishery. 


Water samples were collected in the summer of 2010 from the major tributaries to the Aransas, Copano, San Antonio, and Mission Bay systems. Analyses of these water samples indicate that δ18O and trace element (Sr and Ba) values show significant variation, indicating that if southern flounder in Texas do exhibit a freshwater residency period, it may be possible to assign an individual fish to a particular freshwater habitat. This work will provide fisheries managers with a more informed understanding of habitat requirements of juvenile southern flounder, therefore leading to the implementation of more comprehensive and effective conservation and management strategies.

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