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Sighting, group composition, and tactile exchange for a study on Atlantic spotted dolphins around Bimini, The Bahamas

Citation

Danaher-Garcia, Nicole (2022), Sighting, group composition, and tactile exchange for a study on Atlantic spotted dolphins around Bimini, The Bahamas, Dryad, Dataset, https://doi.org/10.5061/dryad.xwdbrv1g4

Abstract

Interactions between mammalian social groups are generally antagonistic as individuals in groups cooperate to defend resources from non-members. Members of the family Delphinidae inhabit a three-dimensional habitat where resource defense is usually impractical. Here, we describe a long-term partial fusion of two communities of Atlantic spotted dolphins (Stenella frontalis). The northern community, studied for 30 years, immigrated 160 km to the range of the southern community, observed for 20 years. Both communities featured fission-fusion grouping patterns, strongest associations between adult males, and frequent affiliative contact between individuals. For the five-year period following the immigration, we found members of all age classes and both sexes in mixed groups, but there was a strong bias toward finding immigrant males in mixed groups. Some association levels between males, and males and females, from different communities were as high as the highest within-community associations. Affiliative contacts indicate that these individuals were forming social bonds. The mixing of two separate social groups with new bond formation is rare in terrestrial mammal groups. Such mixing between spotted dolphin groups suggests that adaptations to respond aggressively to ‘outsiders’ is diminished in this species and possibly other ecologically similar dolphins.

Methods

Sighting data were collected during boat surveys between 2013-2018 around Bimini, The Bahamas. Group composition data were summarized from sighting data collected between 2007 and 2018. Tactile exchanges were event sampled from underwater video data recorded during boat surveys that had underwater encounters. Tactile exchanges have been limited to events that occurred during mixed-origin sightings (i.e., including dolphins from the resident and immigrant group).

Usage Notes

Analysis of association was completed in Socprog, which runs in MatLab. Code from Socprog cannot be provided, but the settings used to calculate coefficients of association are included in the Methods section of the manuscript.