Assessing Southern Flounder Populations in the Northern Gulf of Mexico

Despite Southern Flounder being a commercially and recreationally important flatfish species in the northern Gulf of Mexico (GOM), our knowledge of its population dynamics is not well developed.  We collected Southern Flounder from three sites along the northern GOM-- Barataria Bay, LA, Mobile Bay, AL, and Apalachicola Bay, FL and used sagittal otoliths to quantify age-and-growth.  Growth was quantified using von Bertalanffy equations and did not differ for fish from Louisiana versus Alabama waters, but differed significantly for fish from Florida waters versus both Louisiana and Alabama.  Significant differences in length-frequency distributions were observed for Southern Flounder across all three regions, being larger in Alabama versus Louisiana and Florida.  We also examined weight-length relationships for these populations (i.e., W = aL^b); exponent b values for Louisiana, Alabama, and Florida were b = 3.2752, b = 3.1788, and b = 2.8448, respectively.   Significant differences in weight-length relationships among sites (all p<0.007) indicate that Southern Flounder collected from Louisiana and Alabama coastal waters put on more weight per length than did fish from Florida coastal waters.  Finally, we used catch-curve analysis to quantify total annual mortality (A) for these populations, which were 79% in Louisiana, 61% in Alabama, and 54% in Florida.