Groups of the little-known Arnoux's beaked whale, Berardius arnuxii, were observed at narrow cracks or leads in sea ice near the Antarctic peninsula during the austral summer of 1992-1993. The whales were grey, had a slightly asymmetric blowhole and blow, and were heavily scarred in adulthood. At least 30 animals were uniquely identified using their scars. Despite often cramped conditions at the breathing holes, the whales were always calm and nonaggressive, reacting to the circumstances with surfacing and submerging behaviour involving little horizontal movement. Seventy dive durations by 17 identified adults were recorded, with a mode of 35-65 min and a maximum of at least 70 min. Eight periods of respiration varied between 1.2 and 6.8 min, with an average of 9.6 blows/min. These breath-hold characteristics confirm B. arnuxii as one of the most accomplished mammalian divers, capable of swimming up to an estimated 7 km between breathing sites in sea ice. Whales moved to and from the observed lead, apparently able to find other breathing sites in what appeared to be unbroken ice. The species seems well adapted to life in ice-covered waters and may be able to exploit food resources inaccessible to other predators in the region.
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