Preliminary Examination of Atlantic Bluefin Tuna Thunnus thynnus Feeding Ecology in the Northern Gulf of Mexico

A preliminary examination of the feeding ecology of bluefin tuna (Thunnus thynnus) on the northern Gulf of Mexico spawning grounds is described using a combination of stomach contents, nitrogen stable isotope values, and tissue C:N values.  Diet data suggest the importance of teleosts, cephalopods, crustaceans, and pelagic tunicates.  Stable isotope values from T. thynnus collected in the Gulf of Mexico did not indicate nutritional stress (i.e., starvation) and muscle lipid stores were greater than those observed in some northern feeding grounds.  This study provides the first evidence that T. thynnus are foraging in the Gulf of Mexico and support the classification of this region as both a feeding and spawning ground for the species.  Our future work will examine diel feeding patterns and gastric evacuation rates of T. thynnus while they are consuming low-lipid prey.  We will also examine relationships between gonad and stomach volume to assess whether feeding rates may be limited by a reduction in intracoelomic space for fish in spawning condition.  Diet data from this region will be contributed to data from areas throughout the range of this species as part of a classification and regression tree (CART) analysis of T. thynnus trophic ecology.