Reproductive biology of female spotted seatrout, Cynoscion nebulosus, in the Gulf of Mexico:: Differences among estuaries?

Although the reproductive biology of spotted seatrout, Cynoscion nebulosus, has been documented across the northern Gulf of Mexico, longitudinal comparisons across its range are not available. We evaluated aspects of female spotted seatrout reproduction in five estuaries ranging from Charlotte Harbor, FL (CHFL) to Redfish Bay, TX (TX). Seasonal temperature profiles were similar among the five estuaries, but spring salinities were lower in Apalachicola Bay, FL (AFL) and St. Louis and Biloxi Bays, MS (MS) (range 7.5-15.0parts per thousand) than in CHFL, Barataria Bay, LA (LA) and TX (range 16.6-31.7parts per thousand). The length of the spawning season varied among estuaries: five months in MS and AFL, six months in LA and TX, and seven months in CHFL. Peak gonodosomatic index (GSI) values varied from May to July among estuaries. The smallest sexually mature females captured ranged from 235 mm TL in LA to 285 mm TL in AFL. Mean relative batch fecundity (# eggs g(-1) ovary-free body weight) was significantly higher (ANOVA, p < 0.5) in TX (390 +/- 39) and LA (397 +/- 26) than in MS (103 +/- 10). Spawning frequency, determined by the percentage of females in the late developing ovarian class with postovulatory follicles, ranged from 4.2 to 7.7 d and was not significantly different when all months were combined. However, significant differences during March, April and September (χ(2), p < 0.01) showed that spotted seatrout from CHFL and AFL spawned less frequently than those from other estuaries. Overall, MS and AFL fish have the shortest reproductive season, fewer number of spawns and appear to obtain sexual maturity at a slightly larger size. Five hypotheses to explain these differences are presented: variations in time of sampling, temperature, habitat structure, genetics and salinity. Differences in salinity profiles appears to be the most plausible explanation.