Seasonal changes in the feeding aggregation structure of male sperm whales (Physeter macrocephalus) in Northern Norway

Abstract

The sperm whale (Physeter macrocephalus) is one of the most widely distributed cetaceans. Adult males commonly occupy high latitudes, whereas females and juveniles occupy lower latitudes. In Northern Norway, previous studies focused on the summer period limiting our understanding of the seasonal dynamics of male foraging aggregations. We used year-round capture–mark–recapture data based on photo identification between 2009 and 2023 to examine seasonal patterns within a male aggregation off Andøya, Northern Norway. Our analysis encompassed 426 days of data, 111 days in winter (October–April) and 315 days in summer (May–September). Among 365 identified individuals, 29% were encountered across multiple years. A higher number of individuals could be identified in winter compared to summer. The mean estimated residency time was shorter in winter (13 days) than in summer (18 days). We identified four groups with distinct seasonal preferences in occurrence and residency, suggesting seasonal and individual foraging and social patterns. Despite the marked seasonal patterns, the relatively short residency times imply this area constitutes only a fraction of the broader foraging range of sperm whales in the Northeast Atlantic. This study highlights the year-round presence of sperm whales in the area, emphasizing their individual seasonal preferences.