Remarkable development of diving performance and migrations of hooded seals (Cystophora cristata) during their first year of life

Newborn hooded seals (Cystophora cristata) have smaller weight-specific oxygen stores than adults, but nothing is known about how this affects their diving behaviour. Here, we present data on the diving behaviour and migrations of seven weaned hooded seal pups of the Greenland Sea stock during their first year of life, as collected by use of satellite telemetry. The pups started diving 1–2 days after tagging, and during a tracking period of 25–398 days they dispersed over vast areas of the Greenland and Norwegian Seas in a manner similar to adults. The initial development of diving depths and durations in April–May was rapid, and pups reached depths of >100 m and dived for >15 min within 3 weeks of age. During early summer (May–June) this development was temporarily discontinued, to be resumed throughout autumn and winter, during which time maximum depths and durations of >700 m and >30 min, respectively, were reached. Depths and durations were significantly related to age/season, location and time of day. The dive behaviour in early summer, with relatively shallow and short dives without diurnal variations, resembles that of adults and probably reflects the vertical distribution of prey rather than physiological constraints. Dives of pups were nevertheless shallower and shorter than those of adults, but relative to body mass both hooded seal pups and adults display a remarkable diving capacity which makes the species particularly suited for studies of defence mechanisms against hypoxia insult in mammals.