Movements and site fidelity of harbour seals (Phoca vitulina) in Kattegat, Denmark, with implications for the epidemiology of the phocine distemper virus

Twenty-seven harbour seals were caught and tagged at the island of Anholt in central Kattegat, Denmark, the epicentre of the phocine distemper virus (PDV) outbreaks in 1988 and 2002 that killed 50–60% of the populations. The satellite tagging shows that harbour seals from Anholt moved widely across Kattegat with a maximum distance of 249 km from the tagging haul-out site. Overall, females
travelled over a wider area compared with males [90% kernel home range (KHR) females, 5189 km2; males, 3293 km2). KHR calculated for yearlings (6414 km2) is larger than for subadults (2534 km2), which again is larger than for adult seals (1713 km2), showing a strong site fidelity, indicating limited gene flow between haul-out sites. Distances moved and home range sizes increased across autumn, peaked in February–March, and decreased through spring. During the breeding season in spring, all seals were very stationary around Anholt. The onset of the PDV epizootics in 1988 and 2002 took place when the Anholt harbour seals congregate on the Island during April. Anholt seal were also documented to have contact with infected seal locations at Hesselø, Læsø, and the Swedish west coast, although this contact takes place during winter prior to the documented summer outbreaks.