Habitat partitioning and fine scale population structure among insular bottlenose dolphins (Tursiops aduncus) in a tropical lagoon

Abstract

Among marine organisms, little is known on patterns of intra-species habitat partitioning, whereas many studies have examined niche segregation at the multi-species community level. In this study, we investigated the fine-scale population structure and patterns of within-species habitat use of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in a tropical lagoon of the Indian Ocean (Mayotte, 45°10′E/12°50′S). First, we assessed genetic population structure using mtDNA and 14 microsatellite markers to determine if bottlenose dolphins around Mayotte belong to one or several panmictic groups. The analyses revealed no mitochondrial polymorphism and the presence of a single population at Hardy–Weinberg equilibrium. Second, we assessed whether a community structure exists within the bottlenose population. A community is an assemblage of individuals using a common home range. Photo-identification data were used to assess individual home range size and habitat preferences. Home range analysis revealed the presence of at least two communities of bottlenose dolphins around Mayotte: one occurring in the shallower waters inside the lagoon and a second in the vicinity of a deeper reef bank, situated further offshore in the northern part of the island. Stable isotope analyses of δ13C and δ15N were performed to detect intra-species segregation of habitat and resource use. However, no significant structure across the population was detected. Nevertheless, this study highlights that, even at small spatial scales, individual and between community variations of habitat preferences occur in bottlenose dolphin populations. Intra-species niche partitioning may explain habitat segregation in these insular delphinids.