Fine‐scale social and genetic structure of common bottlenose dolphins (Tursiops truncatus) in the Barataria Basin, Louisiana, USA

Abstract

Abstract The Barataria Bay Estuarine System (BBES) Stock of common bottlenose dolphins (Tursiops truncatus) in the northern Gulf of Mexico has been a focus of extensive research as a result of the Barataria Basin, Louisiana being one of the most heavily oiled estuaries following the Deepwater Horizon oil spill. The goal of this study was to build upon previous research to better understand social and genetic structure of BBES dolphins. Photo‐identification data from 2010–2019 were analysed with SOCPROG to identify dolphin social clusters. Genetic analyses were conducted on samples obtained during remote biopsy surveys and health assessments (2010–2018) to assess if identified social clusters were congruent with genetic clustering results, and to evaluate relatedness and gene flow within and between social and genetic clusters. Spatial analyses of the cumulative photo‐identification sighting histories from each cluster were also used to determine their geographic range and degree of overlap within the Barataria Basin. Social analyses identified four distinct clusters with some degree of geographic overlap and similar utilization distributions as the three identified genetic clusters. Dolphins in the Barataria Basin were confirmed to be genetically differentiated from those in adjacent coastal waters. In general, genetic analyses differentiate distinct dolphin communities established through long‐term (generational) preferential breeding behaviour. In contrast, social associations can be more fluid over the short‐term, may change in response to habitat or predator/prey changes, and strong associations can be formed between a mix of related and unrelated individuals. The combination of genetic and social methodologies is valuable for developing a better understanding of complex dolphin social interactions and provides unique insights into dolphin behaviour that can be important for developing effective management strategies.