Berardius
Berardius | |
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Photo of Arnoux's beaked whale | |
Illustration of Baird's beaked whale | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Artiodactyla |
Infraorder: | Cetacea |
Family: | Ziphiidae |
Subfamily: | Berardiinae
|
Genus: | Berardius Duvernoy, 1851 |
Type species | |
Berardius arnuxii [1] Duvernoy, 1851
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Species | |
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Arnoux's beaked whale range | |
Baird's beaked whale range |
The four-toothed whales or giant beaked whales are
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. However, genetic evidence and their wide geographical separation has led them to be classified as separate.
While Berardius arnuxii and Berardius bairdii are considered least concern by the IUCN.[8][9] Berardius minimus is labeled as near threatened as of 2023[update].[10]
This article currently largely treats four-toothed whales as monospecific, due to a lack of species-specific information.
Species overview
Berardius was once classified as containing only two species: Arnoux's beaked whale (Berardius arnuxii) in the Southern Hemisphere waters, and Baird's beaked whale (Berardius bairdii) in the North Pacific.
Researchers have debated over whether the northern and southern populations represent distinct species or whether they are simply geographic variants.
It is speculated that the Baird's and Arnoux's whales separated from one another after their common ancestor separated from the kurotsuchi;
Possible species
Sightings during
"Bottlenose whales in the Sea of Okhotsk" had been reported since the time of the Soviet Union's whaling,[28] and an unknown type of beaked whale resembling Baird's beaked whales having four tusks on upper and lower jaws has also been recorded by traditional whalers in Japan.[29] It is unknown whether these records correspond with this new form.
An unknown type of large beaked whale of similar size to fully grown Berardius bairdii have been reported to live in the Sea of Okhotsk, somewhat resembling
Physical description
The two established species, Baird's and Arnoux's beaked whales, have very similar features and would be indistinguishable at sea if they did not exist in disjoint locations.
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.[34] 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.[35] These traits are similar in both sexes, as there is little sexual dimorphism in either species.[33][34] Among the observed differences in the sexes is their size: female Baird's and Arnoux giant beaked whales are slightly larger than the males.[35]
Although fairly similar, there exist some differences between the species. Baird's beaked whales are around 4.6 metres (15 ft) when born, and can reach lengths of 11.1 metres (36 ft) as adults, making them the largest members of the beaked whale family. Members of the Baird's species have fairly narrow body shapes despite their large size, and have dorsal fins that are rounded at the tips. Their coloration is fairly uniform and can range from brown to grey.[34] Arnoux's beaked whales are around 4 metres (13 ft) long as calves and can reach lengths up to 9.75 metres (32 ft) as adults.[33] Their bodies are not as narrow as the Baird's, and resemble a spindle. Unlike the Baird's beaked whale, Arnoux's have slightly hooked dorsal fins.[33] Arnoux's beaked whales have a dark coloration that ranges from brown to orange due to a buildup of algae on its body.[33]
A third species, B. minimus, (known by the Japanese common name "kurotsuchi", which means "black Berardius") was formally named in 2019,
Population and distribution
The total population is not known for two of the three species. Estimates for Baird's are of the order of 30,000 individuals. Nothing is known at all about the population size of the third species of Berardius, first scientifically described in the 2010s.
Arnoux's
Arnoux's beaked whales inhabit great tracts of the
Baird's
Baird's beaked whale is found in the North Pacific Ocean, the Sea of Japan and the southern part of the Sea of Okhotsk.[41] They appear to prefer seas over steep cliffs at the edge of the continental shelf, but are known to migrate to oceanic islands and to near shore waters where deep cliffs locate next to landmasses such as at Rishiri Island and in Tsugaru Strait, Shiretoko Peninsula, Tokyo Bay, and Toyama Bay.[34]
The continental shelf was reported in the Alaska stock report as the whales migrate to the shelf in the summer months during when the water temperature are at the highest.[42] According to the California/Oregon/Washington NOAA stock assessment report the Baird's beaked whales can be found in the deep waters along the continental slopes of the North Pacific Ocean.[11][43][44] They are often seen along the slope between late spring to early fall.
Specimens have been recorded as far north as the
The historic and current status of the northern species in northwestern coastal Pacific outside the Japanese
The seasonal distribution can be observed when the Baird's beaked whales spend the summer months in the Sea of Okhotsk and the Bering Sea between April–May to October. (Tomilin 1957, Kasuya 2002, Alaska Stock assessment report 2017). The wintering habitats is assumed to be located in the northern Gulf of Alaska which was determined by using acoustic detection, (Baumann-Pickering et al. 2012b. and Alaska Stock assessment report 2017.)
Sato's
B. minimus is currently known to reside in only the central and western North Pacific Ocean. The species' range includes portions of Japan, Russia, and Alaska, between 40°N and 60°N and 140°E and 160°W. However, this distribution is based primarily on data collected from stranded specimens, and its range may extend further.[2][38][10]
Behavior
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.[3] Baird's beaked whales generally move in pods of 5 to 20 individuals, with groups of 50 observed in rarer circumstances.[53] Congregating groups of Baird's whales are led by a single large male. Scarring among males indicate competition for this leadership position that must entail more breeding opportunities and gives evidence that the species' behaviors portray sexual selection.[54] Potentially one of the deepest diving cetaceans, they can dive for an hour at a time, predating on deep-water and bottom-dwelling fish, cephalopods, and crustaceans. When not diving, they drift along the surface.[22] The deep diving whales can dive to depths of 800–1,200 metres (2,600–3,900 ft), and when feeding, they generally prefer deep waters near the continental shelf or around seamounts, where high biological activity is present in shallower waters.[55] The deepest recorded dive is 1,777 metres (5,830 ft).[56][57]
Diel variation in behavior suggests that 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.[58] Considering the extent of whaling on the Baird's species, the pod's uninfluenced structure is not well known. To date, two-thirds of the whales caught have been male, despite the fact that females are somewhat larger than males and would be thought to be the preferred targets for whalers.[35] They are listed as least concern under the IUCN Red List[8] and not listed as depleted under the MMPA.[44] They are not being hunted for research due to Japan pulling out of the whaling commission in 2018/2019.
Observations of Arnoux's beaked whales in
Reproduction
Mating in Baird's beaked whales happens in the months of October and November and calving occurs in March and April after a 17-month gestational period.
Feeding
Baird's beaked whale has a diet that consists primarily of deep sea fish and cephalopods found at its preferred dive depths (1000–1777m).[56][57] On rare occasions, it has been known to eat octopus, lobster, crab, rockfish, herring, starfish, pyrosomes and sea cucumbers.[41] Baird's beaked whales in the southern Sea of Okhotsk diet consists of deep-water gadiform fishes and cephalopods.[41] The species has a mean dive time of about 1 hour, which suggests a long search and handling time.[42][41] Its generalist feeding strategy may be reflective of limited prey availability at such depths or regions, as mammals become more general feeding strategists as prey diversity decreases. It may also explain the species' migrational patterns around the North Pacific.[41] In summer months, Baird's beaked whale can be found off the Pacific coast of Japan where demersal fish are abundant.[41] Stomach content analysis's found that Baird's beaked whale feeds in benthic zones both day and night. This behavior differs from its other Odontocete relatives (namely the common dolphin and Dall's porpoise) who feed in mesopelagic regions during the day when the light can penetrate the water column.[66] This suggests that Baird's beaked whale does not rely as much on its sense of sight and has evolved to navigate and hunt competently with echolocation.[67] There is little information on the foraging behavior of Baird's beaked whales and their ecological role in the marine ecosystem.[41]
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).[68]
Baird's beaked whale is listed by the Mammalogical Society of Japan as rare in Japanese coastal waters. The Baird's beaked whale is listed on Appendix II
In the 20th century, Baird's beaked whales were hunted primarily by Japan and to a lesser extent by the USSR, Canada and the United States. The USSR reported killing 176 before hunting ended in 1974. Canadian and American whalers killed 60 before halting in 1966. Japan killed around 4000 individuals before the 1986 moratorium on whaling (about 300 were killed in the most prolific year, 1952). Baird's beaked whales are not protected under the International Whaling Commission's moratorium on commercial whaling, as Japan argues they are a 'small cetacean' species, despite being larger than minke whales, which are protected. Each year, 62 Baird's beaked whales are hunted commercially in Japan, with the meat sold for human consumption. A landing and processing of a Baird's beaked whale was filmed[72] by the Environmental Investigation Agency on 7 August 2009. Meat and blubber food products of the whales have been found to contain high levels of mercury and other pollutants, such as polychlorinated biphenyls (PCBs).
Population status
Estimates of the abundance of populations are unavailable.[44] They are not listed as "threatened" or "endangered" under the endangered species act nor depleted under the MMPA.[44]
Threats
The Baird's beaked whale is hunted by Japan. As of 2019, Japan pulled out of the International Whaling Commission (IWC) to continue harvesting whales commercially.[73] The California large mesh drift gillnet fishery has known to interact with the CA-OR-WA population. There are habitat concerns for the Alaska stock, in areas with oil and gas activities or shipping and military activities are high.[44] For the Baird's beaked whale.[clarification needed][74][75][76] Anthropogenic sound sources such as military sonar and seismic testing. The testing of military sonar has been recorded to effect the diving behavior of beaked whales. This implication on the whales effects their ability to decompress upon surfacing and results in the whales suffering the bends, increase nitrogen gas bubbles in the blood.[22][44]
Common names
- B. arnuxii is known as Arnoux's beaked whale, southern four-toothed whale, southern beaked whale, New Zealand beaked whale, southern giant bottlenose whale, and southern porpoise whale. In Japanese it is known as minami-tsuchi (ミナミツチ), literally "Southern hammer (i.e. Berardius)".
- B. bairdii is known as Baird's beaked whale, northern giant bottlenose whale, North Pacific bottlenose whale, giant four-toothed whale, northern four-toothed whale, and North Pacific four-toothed whale. In Japanese, it is called tsuchi-kujira (ツチクジラ), where tsuchi means "hammer", in reference to the way the head vaguely resembles a traditional Japanese hammer or mallet, and kujira means "whale".[77]
- The newly described species, B. minimus, is traditionally known to Japanese whalers as kuro-tsuchi (黒ツチ),[2] where kuro means "black" and tsuchi means "hammer".[77] The Society for Marine Mammalogy lists Sato's beaked whale as an additional common name for B. minimus.[78]
Specimens
- MNZ MM002654 B. arnuxii Arnoux's beaked whale, collected Riverton, near Invercargill, New Zealand, 27 January 2006
See also
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{{cite journal}}
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- "Giant Beaked Whales" in the Encyclopedia of Marine Mammals pages 519-522 Teikyo Kasuya, 1998. ISBN 0-12-551340-2
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- Whales, Dolphins and Porpoises Carwardine, 1995. ISBN 0-7513-2781-6
- An image of a Baird's Beaked Whale at monteraybaywhalewatch.com
External links
- The Environmental Investigation Agency
- Whale & Dolphin Conservation Society (WDCS)
- Baird's Beaked Whale - ARKive bio
- Arnoux's Beaked Whale - ARKive bio
- Arnoux's beaked whale - The Beaked Whale Resource
- Baird's beaked whale - The Beaked Whale Resource
- Rare whale gathering sighted - BBC News
- Species Convention on Migratory species page on Baird's Beaked Whale
- Voices in the Sea - Sounds of the Baird's (Giant) beaked Whale Archived 9 July 2014 at the Wayback Machine