Social Life in the Deep: Variation in Network Structure and Association Patterns of Rough‐Toothed Dolphins ( Steno bredanensis ) Around the Main Hawaiian Islands

ABSTRACT While coastal delphinid sociality has been extensively investigated across the globe, little is known about the social structure of odontocetes in the open ocean. The rough‐toothed dolphin ( Steno bredanensis ) is a globally distributed oceanic dolphin occurring in tropical and warm‐temperate waters. Around the main Hawaiian Islands, two demographically distinct populations have been identified: one off Kauaʻi and Niʻihau, the other off Hawaiʻi Island. We investigated differences in network structure and association patterns between these populations using photo‐identification data collected from 2002–2020. Social network analysis revealed that the Kauaʻi–Niʻihau population was more subdivided into distinct social clusters (i.e., had higher modularity: 0.58 vs. 0.47) and less densely interconnected (i.e., lower network density: 0.07 vs. 0.12) than the Hawaiʻi Island population. Mean association strength within clusters was higher off Hawaiʻi Island (0.31) than off Kauaʻi–Niʻihau (0.22). Social connections off Hawaiʻi Island also relied more strongly on a smaller number of individuals that linked clusters together. We suggest that differences in population density and habitat extent may contribute to differences in social network structure. Although low re‐sighting rates limited our ability to characterize either population comprehensively, applying identical methods allowed us to identify relative differences in network structure between them.