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IN THE LAB Retracing the Steps of Southern Flounder BEN F. KOCIAN By Megan K. Nims, M.S. The University of Texas Marine Science Institute E


XCITING TO CATCH and delicious to eat, southern flounder is one of the most highly sought fish on the Gulf Coast. Southern flounder supports a large


and important recreational fishery and every year in the late fall and early winter, as adult southern flounder migrate from bays to the Gulf of Mexico to spawn, thousands of fisher- men brave the cold weather to try their hand at gigging flounder.


The Texas Parks and Wildlife Department has implemented management mea- sures, such as a ban on gigging during the month


of November and a stock-enhancement


program, to promote recovery of the stocks.


Over the past several years, howev-


er, southern flounder populations have declined in Texas waters, leading to questions about the sustainability of this important fishery. The Texas Parks and Wildlife Department has imple- mented management measures, such as a ban on gigging during the month


TIDE www.joincca.org 47


of November and a stock-enhance- ment program, to promote recovery of the stocks. Research in the northern Gulf of


Mexico and in North Carolina has shown that juvenile southern flounder spend a lot of time in freshwater habi- tats. It is unclear, however, whether southern flounder in Texas exhibit the same behavior. At the Fisheries and Mariculture Laboratory of the University of Texas Marine Science Institute in Port Aransas, Dr. Benjamin Walther and I conducted a study to determine whether juvenile southern flounder in Texas use freshwater habitats. It is especially important to understand habitat requirements of juvenile fish


because these young stages are a par- ticularly vulnerable period in a fish’s life cycle. So, how is it possible to retrace the


steps of an individual southern floun- der? The answer lies in otoliths, some- times called “ear stones.” These are cal- cified structures located in the inner ears of fish. Otoliths aid in hearing and balance but can also reveal the fish’s age, growth rate, where it was hatched, and its lifetime migration patterns. Much like the rings formed in tree trunks, otoliths grow continuously throughout a fish’s life, incorporating naturally occurring trace elements from the surrounding water as they grow. Since the chemical composition


Otoliths aid in hearing and balance but can also reveal the fish’s age, growth rate, where it was hatched, and its lifetime migration patterns.


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