Stable Carbon Isotope Evidence for Reduced Feeding of Gulf of Mexico Sturgeon during Their Prolonged River Residence Period

Stable carbon isotope ratios were used to delineate food sources for Gulf of Mexico sturgeon (Acipenser oxyrinchus de sotoi), an anadromous fish that migrates between Gulf of Mexico and the coastal rivers in south-east U.S.A. The large difference in isotope ratios (∼11‰) between freshwater food sources and fish muscle tissue suggests that the Gulf of Mexico sturgeon do not feed significantly in fresh waters. Isotope ratio data from this study and also from the literature indicate that the growth of Gulf of Mexico sturgeon is almost entirely supported by coastal marine food sources. It is likely that Gulf of Mexico sturgeon use the cool springs that seep into the river as a thermal refuge during their river residence in summer and that thermal barriers may prevent the fish from exploiting the rich food sources available in the warmer portions of the Suwannee River.