Arnoux's beaked whale (''Berardius arnuxii''), also called the southern four-toothed whale, southern beaked whale, New Zealand beaked whale, southern giant bottlenose whale and southern porpoise whale is one of the species of '' Berardius''. Arnoux's and

Baird's beaked whale Baird's beaked whale (''Berardius bairdii''), also known as the northern giant bottlenose whale, North Pacific bottlenose whale, giant four-toothed whale, northern four-toothed whale and the North Pacific four-toothed whale, is a species of whale ...

s are so similar that researchers have debated whether or not they are simply two populations of the same species, until genetic evidence and their wide geographical separation led them to be classified as separate. Little is known about their behavior due to infrequent encounters with live individuals.

Physical description

Arnoux's and Baird’s beaked whales, have very similar features and would be indistinguishable at sea if they did not exist in disjoint locations. Both whales reach similar sizes, have bulbous

melons A melon is any of various plants of the family Cucurbitaceae with sweet, edible, and fleshy fruit. The word "melon" can refer to either the plant or specifically to the fruit. Botanically, a melon is a kind of berry, specifically a " pepo". Th ...

, and long prominent

beak The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for eating, preening, manipulating objects, killing prey, fighting, probing for foo ...

s. 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. The teeth in the Ziphiidae are presumed to be used by the males for fighting and competition for females. Ziphiidae has 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 body. 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 Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...

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.

Population and distribution

Arnoux's beaked whales inhabit great tracts of the

Southern Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-small ...

. Large groups of animals, pods of up to 47 individuals, have been observed off Kemp Land, Antarctica. Beachings in

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

and

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

indicate the whale may be relatively common in the Southern Ocean between those countries and

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...

; sporadic sightings have been recorded in polar waters, such as in

McMurdo Sound McMurdo Sound is a sound in Antarctica. It is the southernmost navigable body of water in the world, and is about from the South Pole. Captain James Clark Ross discovered the sound in February 1841, and named it after Lt. Archibald McMurdo ...

. It has also been spotted close to South Georgia and

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...

, indicating a likely

circumpolar distribution A circumpolar distribution is any range of a taxon that occurs over a wide range of longitudes but only at high latitudes; such a range therefore extends all the way around either the North Pole or the South Pole. Taxa that are also found in isola ...

. The northernmost stranding was at 34 degrees south, indicating the whales inhabit cool and temperate, as well as polar, waters. There is no stock report for the Arnoux's beaked whale to date by NOAA.

Conservation

Arnoux's beaked whale has rarely been exploited, and although no abundance estimates are available, the population is not believed to be endangered. Arnoux's beaked whale is covered by the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region ( Pacific Cetaceans MOU).

References

{{Taxonbar, from=Q629227 Mammals described in 1851 Ziphiids