Berardius arnuxii has a circumpolar distribution in the southern hemisphere extending from the Antarctic coastline and ice edge (78° S) northward to about 34° S. Most records of sightings and strandings are south of 40° S, but some records occur farther north. A stranded individual was found as far north as 23° S off the coast of Brazil. It is assumed that B. arnuxii mostly occupies deeper, open ocean waters like its northern sister species Berardius bairdii, but there have been numerous sightings of B. arnuxii in shallower coastal waters (less than 500 m depth), and in close proximity to, as well as under, sea ice. Most strandings have occurred around New Zealand.

Biogeographic Regions: antarctica (Native ); atlantic ocean (Native ); pacific ocean (Native )

Berardius arnuxii is one of the largest members of the family Ziphiidae ranging from 8 to 12 m in length, they are second in size only to Berardius bairdii. They have long, tubular bodies and blunt or rounded flippers. The dorsal fin is set far back on the body and is relatively small for a beaked whale (about 3% of the total body length). It has a straight leading edge and concave trailing edge. They have a prominent melon which slopes down into the distinctive ‘beak’ or ‘bottlenose’ of ziphiids. The lower jaw protrudes past the upper jaw. A pair of triangular shaped teeth are present on this protrusion while a second pair of peg-like teeth sit farther back behind a short diastema. These two pairs of teeth are characteristic of the genus Berardius and erupt in both males and females when the individual reaches sexual maturity. A deep V-shaped groove on the throat that consists of folds in the skin and blubber is also distinctive of Berardius. Their blow is a single small puff which is fairly indistinct.

Juveniles are slate grey, while older, sexually mature individuals range from very dark to light grey and are generally lighter on the head. Some individuals may appear brown or green colored due to diatoms attached to the skin. Numerous white scars are apparent on sexually mature individuals and seem to accumulate with time as older individuals have more scarring than their younger counterparts. A greater amount of scarring is also seen on larger individuals. The scars are linear or curved scratch marks occurring on the head, back and sides. Other scar types such as ovals and irregular patches are occasionally seen. No difference in scarring between males and females is apparent. Most of these marks are presumably caused by scratches from the protruding teeth of conspecifics and other objects in their environment such as rock and sea ice. See the Behavior section for more information on conspecific scarring.

Berardius arnuxii is almost identical in appearance to Berardius bairdii. The only real difference is the smaller size of B. arnuxii, but there is considerable overlap in size between the two species. However, the ranges of these two species do not overlap, which greatly simplifies identification.

Range length: 8 to 12 m.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: sexes alike

• Marine

Arnoux’s beaked whales are marine, open ocean dwellers, but they have also been seen in association with Antarctic sea ice and occasionally in shallower coastal waters. Their northern congener, Berardius bairdii, prefers deeper water where they dive to 1000 m to feed. Actual diving depths of B. arnuxii have never been recorded, but dive times of an hour or more indicate that they too may dive to depths of 1000 m.

Habitat Regions: polar ; saltwater or marine

Little is known about the food habits of Berardius arnuxii and most information comes from comparison with B. bairdii. Berardius bairdii is primarily teuthophagous and piscivorous (squid- and fish-eating), but other benthic, epibenthic, and pelagic prey are also eaten. Berardius arnuxii is presumed to have a similar diet with slight variation due to the difference in geographic range. Their association with pack ice suggests that B. arnuxii may be exploiting a unique niche that is not available to most other cetaceans who do not have access to prey found under ice.

Animal Foods: fish; mollusks

Primary Diet: carnivore (Piscivore , Molluscivore )

Arnoux's beaked whales seem to act primarily as benthic predators. They are also hosts for several parasites such as nematodes, trematodes, cestodes, diatoms, cyamid amphipods, and occasional barnacles.

Commensal/Parasitic Species:

• nematodes (Nematoda)
• trematodes (Trematoda)
• cestodes (Cestoda)
• diatoms (Bacillariophyceae)
• cyamid amphipods (Cyamidae)
• barnacles (Cirripedia)

There are no known predators of Arnoux’s beaked whales. However, killer whales (Orcinus orca) occasionally prey on Berardius bairdii in the northern hemisphere. As killer whales occur in the same range as B. arnuxii and utilize many of the same locations, it is possible that a similar relationship occurs, but evidence is currently lacking on this subject.

Barardius arnuxii has a prominent melon and skull structure similar to other odontocetes, indicating that this species uses echolocation for signaling and sensory applications, but little is actually known. Hobson and Martin (1996) observed dolphin-like vocalizations in one group of individuals in ice leads. These clicks and squeaks were made while their heads were above the water line and seemed only to occur while their blowholes were closed. A study by Rogers and Brown (1999) on the acoustic traits of B. arnuxii found that these whales were "highly vociferous" exhibiting whistles, clicks, and click trains similar to other echolocators.

Communication Channels: acoustic

Perception Channels: visual ; acoustic ; ultrasound ; echolocation

Berardius bairdii can live to be 84 years old in males and 54 years old in females. Age in odontocetes (toothed whales) is determined by counting rings in the teeth, similar to the annual rings in a tree. Nothing is known about the lifespan of B. arnuxii, but it is assumed to be similar to that of B. bairdii.

The mating system of B. arnuxii is not known. Scarring on the bodies of males and females may indicate social aggression, possibly around mating, but these behaviors have not been observed.

Little is known about the mating and reproductive habits of Berardius arnuxii. Investigation of the sister species, B. bairdii, is informative, but information on the reproduction of this species is also sparse and debated. Berardius bairdii becomes sexually mature at about 8 to 10 years of age at lengths of 10 m for females and 9.5 m for males. Some researchers claim that females mature first while others state that males mature first and live longer than females. Males are more numerous and older based on research conducted on B. bairdii around Japan, but this could be due to a difference in geographical ranges between the sexes or sampling bias (Kasuya 1986). The gestation period is between 10 and 17 months with a three year interval between birthing events. Calving occurs mostly in the spring, but some births take place from late winter through summer and fall. The mating peak occurs from fall to early winter. Due to their smaller overall size and the few records of mature or pregnant stranded individuals, B. arnuxii seems to mature at younger ages and smaller sizes than B. bairdii.

Breeding interval: Breeding interval in B. arnuxii is unknown.

Breeding season: Breeding seasonality in B. arnuxii is unknown.

Range gestation period: 10 to 17 months.

Key Reproductive Features: iteroparous ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous

Like all mammals, females B. arnuxii invest heavily in their young through gestation and lactation. Otherwise, little is known about parental investment in Arnoux’s beaked whales.

Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female)

Arnoux’s beaked whales are listed under the IUCN red list under the category LR/cd, but no specific threats are listed. They are listed in Appendix I of CITES but are not currently protected under the United States Endangered Species Act. The relatively few sightings imply that B. arnuxii is not common, but little is known regarding its abundance or potential threats.

US Federal List: no special status

CITES: appendix i

State of Michigan List: no special status

IUCN Red List of Threatened Species: no special status

Although B. arnuxii may feed on species used by humans, they do not seem to have any significant impact on any fisheries.

Encounters between humans and Berardius arnuxii are very rare. There is no commercial or subsistence harvesting of this species and they are not caught as by-catch in existing fisheries.