Ontogenetic diet changes in bottlenose dolphins (Tursiops truncatus) reflected through stable isotopes

The ability of stable isotope analysis to provide insight into ontogenetic dietary changes was examined using bottlenose dolphin tooth and skin samples. Teeth were subsampled to compare tissue produced early in life (outer tooth) to that produced later in life (inner tooth). Outer tooth had significantly higher delta N-15 values than the corresponding inner sample from the same tooth (n = 60, P = 0.0041), indicating that there was a temporal shift to a lower delta N-15 diet. There were no significant delta C-13 differences. Higher delta N-15 values in young have previously been attributed to the period of suckling. Analysis of skin tissue from stranded animals of different developmental stages similarly indicated that the delta N-15 values were significantly higher in young animals. Further comparisons indicated that the primary influence for this difference was animals with lengths less than or equal to the largest neonatal dolphin. This difference likely reflects an ontogenetic dietary shift from a sole reliance on milk to a combination of milk and prey species during the first year of life.