Habitat use and diving behaviour of harbour seals in a coastal archipelago in Norway

Background: the harbour seal is coastal non-migratory and suitable for behavioural studies using short-range telemetry and tracking. Methods: a combination of VHF radio telemetry and underwater ultrasonic telemetry was used to obain behavioural and physiological data from 13 harbour seals tagged at an archipelago in Norway. VHF signals were used to locate seals, and they were tracked at close proximity by inflatable boats. Results: transit and foraging activity were identified based on differences in dive profiles. When foraging, all tagged seals operated solitarily, and they returned repeatedly to the same or approximately the same foraging sites. The radio tagged seals used different types of foraging habitats, ranging from shallow kelp areas located 20 km offshore to 150-200 m deep basins with muddy sea bed located a few kilometres from the respective haul-out sites. The seals were typically foraging at or close to the sea bed. Display behaviour including underwater vocalization was recorded for sexually mature males in june and July. Conclusion: the combination of VHF and ultrasonic telemetry is useful for studies of resident seals. Tracking free ranging seals at close proximity made it possible to identify and describe their resting, foraging and display areas.