Stable isotope variation in the northern Gulf of Mexico constrains bottlenose dolphin (Tursiops truncatus) foraging ranges

Site-specific differences were found in consumer isotope values among ten sites examined in the northern Gulf of Mexico. Average δ13C values among sites ranged -21.7 to -15.7 ‰, δ15N ranged <3 ‰: from 9.8 to 11.5 ‰, and δ34S ranged from 5.9 to 18.3 ‰. Isotope variation among these sites provided insight into the ranging habits of bottlenose dolphins (Tursiops truncatus) sampled in St. George Sound (29.8N, 84.6W), a nearshore seagrass habitat, during May of 2005. Isotope comparisons suggest that the majority of dolphins sampled (average ± one standard deviation: δ13C = -17.5 ± 0.8, δ15N = 14.5 ± 0.9, and δ34S = 10.6 ± 1.5) did not forage significantly on offshore species which are significantly 34S-enriched, nor is it likely that they ranged either eastward or westward along the coast within the sampling region. Despite their capability for ranging, these dolphins occupied a restricted home range, during the spring before our sampling efforts. These results demonstrate significant fine-scale isotope variation among coastal habitats explained by differences in freshwater inputs, organic matter loading, and modes of primary production that may be used to constrain the foraging ranges of a highly mobile apex predator. © 2013 Springer-Verlag Berlin Heidelberg.

Duke Scholars

Author Douglas Nowacek Marine Science and Conservation