Feeding ecology of two subspecies of bottlenose dolphin: a tooth tale

Two subspecies of bottlenose dolphins are observed, not simultaneously, in a narrow coastal area of the western South Atlantic Ocean. However, their trophic interaction is unknown. Such information can be explored using stable isotope composition in teeth, warranting time series data. We analyzed carbon and nitrogen isotopic values (δ 13 C and δ 15 N) of dentin growth layer groups in teeth of Tursiops truncatus truncatus and Tursiops truncatus gephyreus stranded along this area of potential co-occurrence in order to investigate the trophic, spatial and temporal dimensions of their isotopic niches. For each subspecies, we calculated isotopic niche width and the possible overlap in resource use between them. We modeled δ 13 C and δ 15 N according to age to verify ontogenetic variations in resources use. We also measured the ratio of individual variation by that of the population to estimate the degree of individual specialization within each subspecies. Mean isotopic values differed only for carbon values (δ 13 C Ttg = − 12.7‰; δ 13 C Ttt = − 14.3‰), and a small overlap in resource use between subspecies was observed. Individual specialization was evident in both subspecies suggesting temporal consistency in resource use and indicating they forage upon various preys. Although weaning age and feeding habit seem similar, subspecies diverge especially in habitat use, indicating they adapted for feeding in different environments. These results show a clear habitat partitioning between subspecies and only a small overlap on resource use within the area, reinforcing the hypothesis of a parapatric distribution with very occasional contacts in this region of the western South Atlantic Ocean.