The four-toothed whales or giant beaked whales are beaked whales in the genus Berardius. They include Arnoux's beaked whale (Berardius arnuxii) in cold Southern Hemispheric waters, and Baird's beaked whale (Berardius bairdii) in the cold temperate waters of the North Pacific. A third species, Sato's beaked whale (Berardius minimus), was distinguished from B. bairdii in the 2010s.

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. It is estimated that the length at birth is ~. Growing up to ~, these are the largest whales belonging to the family Ziphiidae. Sato's beaked whale is much smaller, with adult males having a length of ~.

While Berardius arnuxii and Berardius bairdii are considered least concern by the IUCN, Berardius minimus is labeled as near threatened .

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. Arnoux's beaked whale was described by Georges Louis Duvernoy in 1851. The genus name honors admiral Auguste Bérard (1796–1852), who was captain of the French corvette Le Rhin (1842–1846), which brought back the type specimen to France where Duvernoy analyzed it; the species name honors Maurice Arnoux, the ship's surgeon who found the skull of the type specimen on a beach near Akaroa, New Zealand. Baird's beaked whale was first described by Leonhard Hess Stejneger in 1883 from a four-toothed skull he had found on Bering Island the previous year. The species is named for Spencer Fullerton Baird, a past Secretary of the Smithsonian Institution.

Researchers have debated over whether the northern and southern populations represent distinct species or whether they are simply geographic variants. Several morphological characters have been suggested to distinguish them, but the validity of each has been disputed; currently, it seems that there are no significant skeletal or external differences between the two forms, except for the smaller size of the southern specimens known to date. The morphological similarity gave rise to the hypothesis that the populations were sympatric as recently as the last Pleistocene Ice Age, approximately 15,000 years ago, but subsequent genetic analyses suggest otherwise. Phylogenetic analyses of the mitochondrial DNA control region (D-loop) revealed that Baird's and Arnoux's beaked whales were reciprocally monophyletic — lineages from each of the species grouped together to the exclusion of lineages from the other species. Diagnostic DNA substitutions were also found. These results are consistent with the current classification of Baird's and Arnoux's beaked whales as distinct species. Further, the degree of differentiation between the northern and southern forms of Berardius suggest that the species may already have been separated for several million years.

Possible species

Sightings during whale watching tours and studies of stranded individuals suggest the possibility of another form of Berardius in the Sea of Okhotsk inclusive of the coast of northern Hokkaido especially around Shiretoko Peninsula and off Abashiri, or to Sea of Japan off Korean Peninsula and north pacific and Bering Sea off Alaska. These whales are generally much smaller than known species (), darker in color, and inhabit shallow waters closer to coastal areas, enough to be trapped within fixed nets for salmon. Local whalers had called them "kurotsuchi" (= black Berardius)

"Bottlenose whales in the Sea of Okhotsk" had been reported since the time of the Soviet Union's whaling, 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. 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 Longman's beaked whale. The "Moore's Beach monster", an initially unidentified carcass found in 1925 on Moore's Beach on Monterey Bay, was identified by the California Academy of Sciences as a Baird's beaked whale. There have been claims that records of strandings of these whales exist along the areas within and adjacent to Tatar Strait in the 2010s.

Physical description

thumb|left|Size of Baird's beaked whale compared to an average human

thumb|left|Size of Arnoux's beaked whale compared to an average human

thumb|left|Size of Sato's beaked whale compared to a human

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. 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 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. after being distinguished in 2016, based on differences in haplotypes from mtDNA. It generally has a short beak (~4% body length). While other four-toothed whales are generally grey with scars, kurotsuchis usually have few linear scars, so that the dark, smooth skin contrasts highly with round, white scars of about 5 cm diameter (from cookiecutter shark bites). Beachings in New Zealand and Argentina indicate the whale 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. It has also been spotted close to South Georgia and South Africa, indicating a likely circumpolar distribution. 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.

Baird's

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Baird's beaked whale is found in the North Pacific Ocean, the Sea of Japan and the southern part of the Sea of Okhotsk. 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. They are often seen along the slope between late spring to early fall.

Specimens have been recorded as far north as the Bering Sea and as far south as the Baja California Peninsula. They are also found on the east side and the southern islands (Izu and Bonin Islands) of Japan on the west although it is unclear whether records at these islands are of Berardius bairdii. Southern limits of historical occurrences in east Asian were unclear, while there had been either a stranding or a catch in East China Sea at Zhoushan Islands in the 1950s, and was a disentanglement at Kamae, Ōita. Whales off the east coast of North America seems to approach coasts less frequently than in the western North Pacific, but they may travel further south than in Japan. Historical distributions of southward migrations or vagrants in Asian waters are unknown as the whales wintering from Bōsō Peninsula and in Tokyo Bay to Sagami Bay and around Izu Ōshima have been severely depleted or nearly wiped out by modern whaling (recently whalers shifted their major hunting grounds from Bōsō Peninsula to further north due to the very small numbers of whales still migrating to the former habitats). Within the Sea of Japan, the first scientific approaches to the species were made in Peter the Great Gulf, and the whales can widely distribute more on Japanese archipelago from west of Rebun Island to west of Oki Islands on unknown regularities, and major whaling grounds were in Toyama Bay and Oshima Peninsula. Capture records by Japanese whalers suggest that there may have been historical migrant groups of Baird's beaked whales that once regularly reached the Yellow and Bohai Seas, especially around the island of Lingshan off Jiaozhou Bay and off Dalian, This may have included regions at least as far south as the Zhoushan archipelago. Canada; Japan; Korea, Democratic People's Republic of Korea; Mexico; Russian; United States, (Taylor et al. 2008). Endemic to the North Pacific Ocean and the adjacent seas. There are two different stocks of Baird beaked whales that the National Oceanic and Atmospheric Administration (NOAA) keeps track of for management of the species, the Alaska stock and the California-Oregon-Washington stock. (NOAA website). According to the Alaska 2017 stock report, the range of the Baird's beaked whale is north of the Cape Navarn (62<sup>o</sup> N) and Central Sea of Okhotsk (57<sup>o</sup> N) that spans to St. Matthew Island, the Pribilof Islands, and the northern Gulf of Alaska. (Alaska Stock assessment report and Balcomb 1989).

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

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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. 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. 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. The deepest recorded dive is .

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.

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. and in 2010 indicate that this species may possess a form of bond to locations similar to those of other species such as right whales. Another 4 or 5 sightings have been recorded in the Doubtful Sound between 2007 and in 2011. 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. Males are recorded to live longer. Males live 39 years longer than females with the adult sex ratio strongly biases toward males and the female's exhibit high annual ovulation. Females are slightly larger than the males and exhibit high annual ovulation and pregnancy rates. Males live about 30 years longer than the females with this sex ratio biased toward males it is speculated that the males provide alloparetnel care to offspring which in turn allows the females to have a shorten birth interval frequency. Baird's beaked whales in the southern Sea of Okhotsk diet consists of deep-water gadiform fishes and cephalopods. 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. There is little information on the foraging behavior of Baird's beaked whales and their ecological role in the marine ecosystem.

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 of the convention on the Conservation of Migratory Species of Wild Animals (CMS). It is listed on Appendix II 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. 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. 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. 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.

  • The newly described species, B. minimus, is traditionally known to Japanese whalers as kuro-tsuchi (黒ツチ),

See also

  • List of cetaceans

References

  • "Giant Beaked Whales" in the Encyclopedia of Marine Mammals pages 519-522 Teikyo Kasuya, 1998.
  • National Audubon Society Guide to Marine Mammals of the World Reeves et al., 2002. .
  • Whales, Dolphins and Porpoises Carwardine, 1995.
  • An image of a Baird's Beaked Whale at monteraybaywhalewatch.com
  • MNZ MM002654 B. arnuxii Arnoux's beaked whale, collected Riverton, near Invercargill, New Zealand, 27 January 2006
  • The Environmental Investigation Agency
  • Whale & Dolphin Conservation Society (WDCS)
  • Baird's Beaked Whale - ARKive bio
  • Arnoux's Beaked Whale - ARKive bio
  • 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