Deep diving harbor seals (Phoca vitulina) in South Greenland: movements, diving, haul-out and breeding activities described by telemetry

Abstract

Harbor seals (Phoca vitulina) were formerly widely distributed in Greenland, but in most areas, they have now become rare or extinct. In this study, we deployed 15 satellite-linked data-recorders on 12 individual harbor seals captured near the southern tip of Greenland. The tagging site, a small archipelago, turned out to be their main haul-out and molting location. The seals were tagged around the first week of September across 2 years. Six adult seals transmitted during the breeding season (June–July), during which two males and a female stayed near the tagging site, whereas two females and a male made a targeted swim about 250 km northward along the east coast, just prior to parturition and they returned right after the breeding period. Based on behavior (strong site fidelity and abrupt changes in haul-out and diving activities), we determined that all three females gave birth and that parturition happened during 14–21 June. Prolonged haul-out, relating to the molt, started in early August and peaked during 15 August–8 September with an average of 10–11 h haul-out per day. The seals thereafter gradually transitioned toward a winter mode with more deep dives and on average hauling out 4 h every other day. Dives deeper than 400 m made up less than 1% of their dives, but four seals dove to depths in excess of 575 m, with a record depth of 631 m and the longest dives lasting between 20 and 25 min. To our knowledge, these dives are the deepest recorded for harbor seals.