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

摘要

Site-specific differences were found in consumer isotope values among ten sites examined in the northern Gulf of Mexico. Average δ~(13)C values among sites ranged -21.7 to -15.7 ‰, δ~(15)N ranged ＜3 ‰: from 9.8 to 11.5 %, and δ~(34)S 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: δ~(13)C =-17.5 +- 0.8, δ~(15)N = 14.5 +- 0.9,andδ~(34)S = 10.6 +- 1.5) did not forage significantly on offshore species which are significantly ~(34)S-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.