Berardius
The four-toothed whales or giant beaked whales are beaked whales in the genus Berardius. They include Arnoux's beaked whale in cold Southern Hemispheric waters, and Baird's beaked whale in the cold temperate waters of the North Pacific. A third species, Sato's beaked whale, 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. Lifespan estimates, based on earwax plug samples, indicate male whales can live up to 84 years, while females can have a lifespan of 54 years. 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 as of 2023.
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 in the Southern Hemisphere waters, and Baird's beaked whale in the North Pacific. Arnoux's beaked whale was described by Georges Louis Duvernoy in 1851. The genus name honors admiral Auguste Bérard, who was captain of the French corvette Le Rhin, 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 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.
It is speculated that the Baird's and Arnoux's whales separated from one another after their common ancestor separated from the kurotsuchi; however, this is not certain. The Berardius sp. are deep divers that can spend long periods of time submerged below the surface of the water and thus are difficult to study.
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" or "karasu" ; it is not known whether these terms are synonyms or identify two separate species. Genetic studies indicate that kurotsuchi are Berardius minimus, recognized as a distinct species in 2019."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
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 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 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.
Although fairly similar, there exist some differences between the species. Baird's beaked whales are around when born, and can reach lengths of 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. Arnoux's beaked whales are around long as calves and can reach lengths up to as adults. 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. Arnoux's beaked whales have a dark coloration that ranges from brown to orange due to a buildup of algae on its body.
A third species, B. minimus, was formally named in 2019, after being distinguished in 2016, based on differences in haplotypes from mtDNA. It generally has a short beak. 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. The tip of the rostrum is also white. The kurotsuchi is shorter than other four-toothed whales, around long at maturity, hence the species name, B. minimus. No females of this species have yet been described in the research literature.
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. Baird's and Arnoux's beaked whales have an allopatric antitropical distribution; kurotsuchis are known to live in the North Pacific.Arnoux's
Arnoux's beaked whales inhabit great tracts of the Southern Ocean. Large groups of animals, pods of up to 47 individuals, have been observed off Kemp Land, Antarctica. 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
Baird's beaked whale is found in the North Pacific Ocean, the Sea of Japan and the southern part of the Sea of Okhotsk. 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.The continental shelf was reported in the Alaska stock report as the whales migrate to the shelf in the summer months when the water temperature are at the highest. 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 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. 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.
Baird's beaked whales are not found in southern Chinese waters because they prefer cooler waters, but may be seasonal in colder northern waters. 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. 12 individuals were caught as by-catch along the east coasts of the Korean Peninsula between 1996 and 2012. Canada; Japan; Korea, Democratic People's Republic of Korea; Mexico; Russian; United States,. 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 keeps track of for management of the species, the Alaska stock and the California-Oregon-Washington stock.. According to the Alaska 2017 stock report, the range of the Baird's beaked whale is north of the Cape Navarn and Central Sea of Okhotsk that spans to St. Matthew Island, the Pribilof Islands, and the northern Gulf of Alaska..
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.. The wintering habitats is assumed to be located in the northern Gulf of Alaska which was determined by using acoustic detection,