An assessment of sperm whale occurrence and social structure off São Miguel Island, Azores using fluke and dorsal identification photographs

Abstract

AbstractFemale and immature sperm whales form stable social units in tropical to subtropical waters. One such area is the Azores archipelago, where details of their year‐round occurrence and social organization are not well known. We used year‐round sightings data collected from whale watching vessels to assess sperm whale occurrence and social structure off São Miguel Island, Azores from 2010 to 2017. Individuals were photo‐identified by their flukes (n = 393) and dorsal pigmentation marks were examined to explore their use in assisting with reidentifications. Of all cataloged whales, 78.8% were sufficiently distinctive to be reidentified from dorsal pigmentation patterns. Associations between individuals were analyzed to determine social structure and delineate social units. We identified 12 units comprising 2–13 members that had stable, and perhaps preferred associations for periods up to the eight years of the study. Preferences between some pairs of units may exist, but more research is required to better understand dynamics within and between units. This local scale study is an important contributor to our knowledge of geographic variation on a global scale. We recommend making use of all available information from the entire archipelago, to further increase our understanding of sperm social organization in the Azores.