Arnoux's beaked whale (Berardius arnuxii) is one of the species of beaked whales found in great tracts of the Southern Ocean. Little is known about their behavior due to their secretive nature and infrequent encounters with live individuals.
Arnoux's and Baird's beaked whales are so similar that researchers have debated whether or not they are simply two populations of the same species. Both whales reach similar sizes, have bulbous melons, and long prominent beaks. Their lower jaw is longer than the upper, and once sexual maturity is reached the front teeth are visible even when the mouth is fully closed. The Baird's and Arnoux's beaked whales are the only whales in the Ziphiidae family where both sexes have erupted teeth which are presumed to be used by males for fighting and competition for females. Members of this family have the most prevalent and pronounced markings caused by teeth scaring among the cetaceans. Front-facing teeth may be covered in barnacles after many years. Baird's and Arnoux's beaked whales have similarly shaped small flippers with rounded tips, and small dorsal fins that sit far back on their bodies. Adult males and females of both species pick up numerous white linear scars all over the body as they age, and these may be a rough indicator of age. These traits are similar in both sexes, as there is little sexual dimorphism in either species. Among the observed differences in the sexes is their size: female Baird's and Arnoux giant beaked whales are slightly larger than the males.
Large pods of Arnoux’s whales have been observed off Kemp Land, Antarctica. Beachings in New Zealand and Argentina indicate that these whales may be relatively common in the Southern Ocean between those countries and Antarctica; sporadic sightings have been recorded in polar waters, such as in McMurdo Sound. They have also been spotted close to South Georgia and South Africa, indicating a likely circumpolar distribution. These whales inhabit cool and temperate, as well as polar, waters. They have been found in shallow, coastal waters, near continental slopes and seamounts. Arnoux’s beaked whales are presumed to migrate seasonally away from the edge of the ice in winter to warmer regions for breeding.
Little is known about the behavior of Arnoux's beaked whale, but it is expected to be similar to that of Baird's. Distinctions between the two species are so slight that they are speculated to be the same, although genetic makeup and geographic distribution offer evidence otherwise. Baird's beaked whales generally move in pods of 5 to 20 individuals, with groups of 50 observed in rarer circumstances. Congregating groups of Baird's whales are led by a single large male. Potentially one of the deepest diving cetaceans, they can dive for an hour at a time, predating on deep-water and bottom-dwelling prey. When not diving, they drift along the surface. The deep-diving whales can dive to depths of 800-1,200 meters (2,600-3,900 ft), and when feeding, they generally prefer deep waters near the continental shelf or around seamounts. Beaked whales spend less time at the surface during the day than they do at night, so as to avoid surface predators like sharks and Killer whales. Underwater recordings, made in the austral summer in the Antarctic of a large group of 47 Arnoux's beaked whales showed that they were highly vociferous animals at this time. The whales produced clicks, click trains, and frequency-modulated pulses and whistles which gives their vocalizations a characteristic warbling aural impression. The group swam in coordinated positions along the ice edge, some of them splitting and reassembling.
Arnoux’s beaked whale has a carnivorous (piscivorous) diet that consists primarily of deep-sea fish, cephalopods, and crustaceans.
Little is known about the reproductive behavior of Arnoux’s beaked whales but it is thought to be similar to Baird’s beaked whales. The breeding season of Baird's beaked whales takes place in the months of October and November. Calving occurs in March and April after a 17-month gestational period. Scarring among males indicates competition for a leadership position that must entail more breeding opportunities.
Arnoux’s beaked whales are not threatened at present, however, like other beaked whales, they may suffer from loud underwater sounds, ingestion of plastic in the ocean, and global climate change on the marine environment.
The IUCN Red List and other sources don’t provide the number of the Arnoux’s beaked whale total population size. Currently, this species is classified as Least Concern (LC) on the IUCN Red List.
