Data Sheet 1_Trans-Atlantic movements of Atlantic white-sided dolphins, Leucopleurus acutus.docx

Atlantic white-sided dolphins are wide-ranging and abundant cetaceans of the North Atlantic, yet their movements remain poorly understood. Using satellite telemetry, we tracked 23 dolphins tagged in the Faroe Islands to investigate their movement patterns, habitat use, and diving behavior. Our findings confirm a strong association with the shelf edge and identify the Irminger Sea and the Faroe-Shetland Channel as important regions. The observed movements align with oceanographic features that enhance productivity and prey availability, including strong mixing zones and the Irminger Gyre with deep mixed layers. Three dolphins independently undertook trans-Atlantic migrations to the Irminger Sea, where two remained for extended periods (26 and 63 days). Together with dive records and lower move persistence, this suggests that the Irminger Sea functions as an important autumn feeding ground. Dive data (n = 4) revealed a wide depth range (3–616 m) and diel diving patterns consistent with exploitation of vertically migrating mesopelagic prey. Identifying critical habitats and understanding trans-Atlantic connectivity are essential for effective conservation and management of this species, particularly given ongoing environmental changes in the North Atlantic. The post-release separation of tagged dolphins reflects their fluid social structure, suggesting a panmictic stock in the central and eastern North Atlantic. The study highlights the value of movement data for understanding habitat use, distribution, effect of ocean dynamics, and population structure in pelagic predators.