Arnoux's beaked whale (scientific name: Berardius arnuxii ) is one of 21 species of beaked whales (Hyperoodontidae or Ziphiidae), medium-sized whales with distinctive, long and narrow beaks and dorsal fins set far back on their bodies. They are marine mammals within the order of cetaceans.
|Arnoux's beaked whale. Source: Wurtz-Artescienza|
|Size comparison of an average human against Arnoux's beaked whale. Source: Chris Huh|
Arnoux's beaked whale is very closely related to Baird's beaked whale, the other member of the genus Berardius. In fact, some reserach have suggested that they are the same species with differences in size and range. However, analysis of "mitochondrial and nuclear intron sequence data has however revealed multiple fixed genetic differences, confirming that these species are reproductively isolated and valid taxonomic entities (Dalebout 2002). The latin species name has frequently been misspelled arnouxi or arnuxi." (IUCN)
Arnoux’s beaked whales are marine, open ocean dwellers in the Southern hemisphere, but they have also been seen associated with Antarctic sea ice and occasionally in shallower coastal waters. Baird's beaked whale, in contrast are found in the northern hemisphere in the Pacific Ocean.
Little is known directly about Arnoux’s beaked whales, as they rarely come into contact with humans. Much of what is known about them is inferred from they more well known Baird's beaked whale.
The name beaked whale comes from the way the long snout, or rostrum, tapers to a tip. From above, the rostrum looks like the neck of a bottle, and another common name for the species is giant bottlenose whale. Berardius members have four teeth in the lower jaw. Two of the teeth project from the jaw and may be used for fighting: it is common for the skin of both males and females to be heavily covered in tooth-scars all over the body. The whales feed in deep water, diving for as long as an hour at a time to eat squid, octopus, skates, and other species that are found 2000 metres (m) below the surface. Fifty or more whales often travel together, occasionally breaching and slapping their flippers.
Arnoux's beaked whale is one of the largest members of the family Ziphiidae ranging fromeight to twelve m in length, they are second in size only to Baird's beaked whale. They have long, tubular bodies and blunt or rounded flippers; total length is eight to twelve metres. The dorsal fin is set far back on the body and is relatively small for a beaked whale (about three percent 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. (Balcomb III, 1989; Folkens et al., 2002; Hobson and Martin, 1996) 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. (Balcomb III, 1989; Folkens et al., 2002; Hobson and Martin, 1996; Kasuya, 1986)
Arnoux's beaked whale is almost identical in appearance to Berardius bairdii. The only real difference is the smaller size of Arnoux's beaked whale, 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. (Balcomb III, 1989; Folkens et al., 2002; Hobson and Martin, 1996) Some key physical features are: endothermic ; homoiothermic; bilateral symmetry; little sexual dimorphism.
Key species behaviors are: natatorial; motile; nomadic; migratory; social. Arnoux’s beaked whales are generally seen in groups of five to ten individuals, although larger temporary groups of up to 80 are sometimes observed. They seem to dive and then surface as a group. While at the surface they remain in close proximity to each other and respire for one to eight minutes or about 15 breaths. They slowly swim forward while respiring in the open ocean and remain mostly stationary while surfacing near ice. Average dive times are usually 10 to 45 minutes, but longer dives up to about 70 minutes also occur.
They have been sighted near the pack ice edge and well into the pack ice in leads or open holes in the ice off the Antarctic coast. Some individuals have been trapped in closing ice and subsequently died, but it is unknown whether this is a common cause of mortality. (Balcomb III, 1989; Folkens et al., 2002; Hobson and Martin, 1996; Ohizumi et al., 2003; Ponganis, Kooyman, and Castellini, 1995; Stevick, McConnell, and Hammond, 2002)
Profuse scarring on mature individuals indicates some sort of social interaction between individuals, presumably aggressive. Most of the scars are linear and often parallel which corresponds with the exposed posterior teeth. One hypothesis for scarring in Berardius and other cetaceans is that it serves as a quality signal in competing males. This may apply to Arnoux's beaked whale, but the presence of scarring and teeth in both females and males may indicate that such displays are not limited to one sex. (Balcomb III, 1989; Folkens et al., 2002; Hobson and Martin, 1996; MacLeod, 1998)
Arnoux's beaked whale 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 Arnoux's beaked whale found that these whales were "highly vociferous" exhibiting whistles, clicks, and click trains similar to other echolocators. (Balcomb III, 1989; Hobson and Martin, 1996; Rogers and Brown, 1999) Perception channels include: visual ; tactile ; acoustic ; ultrasound ; echolocation ; chemical .
Virtually nothing is known about the lifespan of Arnoux's beaked whale, but it is assumed to be similar to that of Baird's beaked whales. Baird's beaked whales 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. (Balcomb III, 1989; Boness, Clapham, and Mesnick, 2002; Folkens et al., 2002; Hohn and Fernandez, 1999)
Key reproductive features are: iteroparous; gonochoric/gonochoristic/dioecious (sexes separate); sexual; viviparous. Little is known about the mating and reproductive habits of Arnoux's beaked whale. Investigation of the sister species, Baird's beaked whales, is informative, but information on the reproduction of Baird's species is also sparse and debated.
Baird's beaked whales become 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, Arnoux's beaked whale seems to mature at younger ages and smaller sizes than B.bairdii. (Balcomb III, 1989; Boness, Clapham, and Mesnick, 2002; Folkens et al., 2002) Like all mammals, female Arnoux's beaked whales invest heavily in their young through gestation and lactation. Otherwise, little is known about parental investment in Arnoux’s beaked whales.
Distribution and Movements
Arnoux's beaked whale 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.
The IUCN Red List adds the following details: "Nowhere within this range are they very well known or considered common. Most of the reported sightings are from the Tasman Sea and around the Albatross Cordillera in the South Pacific. The overwhelming majority of strandings have been from around New Zealand (Balcomb 1989, Jefferson et al. 1993). The northernmost records are strandings from Brazil, Argentina, South Africa, and Australia (Paterson and Parker 1994, Culik 2004)."
It is assumed that Arnoux's beaked whale mostly occupies deeper, open ocean waters like its northern sister species Baird's beaked whales, but there have been numerous sightings of Arnoux's beaked whale
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, Baird's beaked whale, prefers deeper water where they dive to 1000 m to feed. Actual diving depths of Arnoux's beaked whale have never been recorded, but dive times of an hour or more indicate that they too may dive to depths of 1000 m. (Balcomb III, 1989; Folkens et al., 2002; Hobson and Martin, 1996; Kasuya, 1986; Ponganis, Kooyman, and Castellini, 1995; Stevick, McConnell, and Hammond, 2002)
Little is known about the predation habits of Arnoux's beaked whale, and most information comes from inference with Baird's beaked whale. Baird's beaked whale is primarily teuthophagous and piscivorous (squid- and fish-eating), but other benthic, epibenthic, and pelagic prey are also eaten, including a variety of mollucks. Arnoux's beaked whale is presumed to have a similar diet with slight variation due to the difference in geographic range. Their association with pack ice suggests that Arnoux's beaked whale may be exploiting a unique niche that is not available to most other cetaceans who do not have access to prey found under ice. (Balcomb III, 1989; Folkens et al., 2002; Hobson and Martin, 1996; Kasuya, 1986; Ohizumi et al., 2003)
There are no known predators of Arnoux’s beaked whales. However, Killer whales (Orcinus orca) occasionally prey on Baird's beaked whale in the northern hemisphere. As Killer whales occur in the same range as Arnoux's beaked whale and utilize many of the same locations, it is possible that a similar relationship occurs, but evidence is currently lacking on this subject. (Balcomb III, 1989; Hobson and Martin, 1996; Stevick, McConnell, and Hammond, 2002)
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. (Balcomb III, 1989)
Economic Importance for Humans
Although Arnoux's beaked whales may feed on species used by humans, they do not appear to have any significant impact on any fisheries. (Balcomb III, 1989; Folkens et al., 2002) Encounters between humans and Arnoux's beaked whale are very rare. There is no commercial or subsistence harvesting of this species, and they are not documented to be caught as bycatch in existing fisheries. (Balcomb III, 1989; Folkens et al., 2002)
Threats and Conservation Status
The IUCN Red List notes:
There are no abundance estimates available for this species (Kasuya 2002), but in comparison with the sympatric southern bottlenose whale, Arnoux’s beaked whale is considered uncommon. In general, the species may be naturally rare. However, Arnoux's beaked whales seem to be relatively abundant in Cook Strait, at least during summer, and are also concentrated south of New Zealand and South America.
There is no information on trends in the global abundance of this species.
Arnoux’s beaked whale has never been hunted to any significant degree, and direct anthropogenic threats are not known. However, a few whales have been taken for scientific study (see Jefferson et al. 1993). Considering that some beaked whale species are known to be vulnerable to large-mesh pelagic driftnets (e.g. Californian drift-netting for swordfish and sharks (Barlow and Cameron 2003)), it is highly likely that Arnoux’s beaked whales were caught in the large-scale drift-netting in the Tasman sea. Although current levels of bycatch are unknown, they are likely to be low due to adoption in 1989 of resolution 44/225 of the UN General Assembly, which called for effective conservation and management measures of living marine resources in areas of high seas drift-netting. Developing high-latitude fisheries, such as that for Antarctic toothfish, a significant proportion of which is illegal and unregulated, have the potential to reduce food available for large predators.
Arnoux's beaked whales have been reported trapped in sea ice, which may contribute to natural mortality. In recent years, there has been increasing concern that loud underwater sounds, such as active sonar and seismic operations, may be harmful to beaked whales (Malakoff 2002). The use of active sonar from military vessels has been implicated in mass strandings of a number of beaked whales including several Mesoplodon species and Indopacetus pacificus (Balcomb and Claridge 2001, Jepson et al. 2003, Cox et al. 2006, Wang and Yang 2006). Sound impacts may be important for all ziphiid species. However, this species’ range probably puts it largely outside the major areas of such impacts.
Predicted impacts of global climate change on the marine environment may affect this species of whale, given its cool-temperate to sub-Antarctic habitat, although the nature of impacts is unclear (Learmonth et al. 2006).
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. (Balcomb III, 1989; Folkens et al., 2002)
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