Sexual Segregation of Coastal Bottlenose Dolphins (Tursiops truncatus) in the Southwestern Gulf of Mexico

Abstract

Cetaceans are highly mobile species with complex social structures, aspects that play an important role in their fitness such as survival and offspring production. Population dispersal influences the dynamics of social species, which may vary with age, sex, or individual status, thus resulting in segregation; however, sex-related dispersal and social affiliations have been studied only in a handful of species at few locations. We conducted a 2-y photographic survey in an open habitat off the coast of Mexico to determine if site fidelity, residency, and social affiliations in male and female bottlenose dolphins (Tursiops truncatus) revealed sexual segregation. Forty-one surveys yielded 167 h of field effort and 61 h of observations. From 174 different individuals, we sexed 38 females and 11 males (45% positively and 55% tentatively). Females were more resident (p < 0.05), had higher site fidelity (p < 0.05), and had weaker associations (p < 0.05) with a higher number of partners (p < 0.05) than males and putative males. Associations were not dictated by differences in sample size or temporal patterns between sexes, and 53% of recorded partnerships were preferred/ avoided relationships. Although the composition of social interactions in the community was highly dynamic, it unveiled evidence of sexual segregation. Temporal and social patterns suggest that males may be primarily responsible for gene flow among adjacent locations. Female associations occurred within a large but unstable network, potentially resembling “bands”; conversely, males and putative males only grouped in pairs or trios, showing significant temporal changes in their relationships, and potentially resembling firstand second-order alliances. Detailed behavioral and genetic data are needed to unravel the social dynamics of this dolphin community and the mechanisms driving their evolutionary change.