Andrews' beaked whale (Mesoplodon bowdoini)

In brief

Andrews' beaked whale is one of the most enigmatic cetaceans on the planet: described in 1908, it has never been identified with certainty alive at sea. Everything known about it comes from a few dozen carcasses stranded on the shores of the southern hemisphere, mainly in New Zealand and southern Australia. This stocky mesoplodont beaked whale of cold temperate and subantarctic waters is classed as “Data Deficient” by the IUCN.

Identification

Mesoplodon bowdoini is a small ziphiid with a fusiform body, but one distinctly more massive than that of most mesoplodont beaked whales, with a girth that can reach more than half the total length. The melon is low and only slightly domed, extended by a short, thick rostrum. The dorsal fin, small and triangular, is set well back on the body; the flippers are narrow and fold into “flipper pockets”, lateral depressions that reduce drag during dives. The tail fluke is broad and lacks a marked median notch, a classic character of beaked whales, even if some specimens show a slight indentation.

The most striking feature concerns the lower jaw of adult males: it rises in a pronounced arch at the middle of the rostrum, bearing a pair of flattened, triangular, tusk-like teeth that protrude above the upper jaw. In females and immatures, these teeth remain buried in the gum and the species then appears toothless. Tooth growth accelerates abruptly in males from about 3.90 m in total length: the largest tooth known from an adult male reached 136 mm in height for 77 mm in length, and an individual from Tierra del Fuego had teeth about 190 mm high. Coloration differs between the sexes: adult males are dark brown to blackish, with the tip of the rostrum and the lower jaw white or very pale, and a body often streaked with long white linear scars left by fighting between males. Females are slate grey to bluish grey on the back, lightening on the flanks and the belly. Both sexes frequently bear oval or circular scars left by the cookiecutter shark (Isistius brasiliensis).

Confusions are numerous and identification often requires examination of the skull. At sea, the species cannot be told apart from the other southern mesoplodont beaked whales: Gray's beaked whale (M. grayi), the strap-toothed whale (M. layardii), Hector's beaked whale (M. hectori), the spade-toothed whale (M. traversii). Morphologically, the most troubling resemblance concerns Hubbs's beaked whale (M. carlhubbsi), a North Pacific species: the females and subadult males of the two species resemble each other so closely that northern hemisphere specimens were long reported as M. bowdoini, in particular in 1946 (in reality M. carlhubbsi) and in 1962 in Japan (in reality M. stejnegeri). These attributions are now invalidated: M. bowdoini is exclusively southern.

Taxonomy

The species was described in 1908 by the American naturalist Roy Chapman Andrews, from a specimen collected in 1904 on the beach at New Brighton, in the province of Canterbury (New Zealand). The epithet bowdoini honours George S. Bowdoin, a donor and trustee of the American Museum of Natural History, where the holotype is held.

Mesoplodon bowdoini Andrews, 1908 belongs to the genus Mesoplodon, by far the richest of the cetaceans with sixteen extant species recognised, the latest, Mesoplodon eueu, having been described only in 2021, and to the family Ziphiidae Gray, 1850 (beaked whales). The name Hyperoodontidae, still used in some classifications and older databases, designates the same family: it is today regarded as a non-accepted synonym of Ziphiidae by the marine taxonomic reference systems. No subspecies is described.

Phylogenetically, Mesoplodon bowdoini, M. carlhubbsi and M. stejnegeri form a set of morphologically close species that Moore interpreted in 1963 as three geographical “groups”: subarctic, north temperate and south temperate. Mitochondrial DNA analyses confirm that these are indeed three genetically distinct species, despite the persistence of cranial resemblances and very similar colour patterns in females and subadults.

Distribution and habitat

Andrews' beaked whale is strictly confined to the southern hemisphere. Its distribution is presumed to be circumpolar, within a band of cold temperate and subantarctic waters lying north of the Antarctic Convergence: the known strandings range between 32° and 54°30' south latitude in the south-west Pacific and the Indian Ocean, and between 36° and 52° south in the Atlantic according to the synthesis by Baker (2001), the Atlantic northern limit having since been pushed back to 33°54' S by the Uruguayan stranding of 2003. The species appears to favour deep oceanic waters, beyond the continental shelf, within a surface temperature range of about 10 to 20 °C.

The documented stranding localities are concentrated in New Zealand, which alone accounts for nearly half the known cases, and on the southern coasts of Australia, Tasmania included. To these are added Macquarie Island, the Tristan da Cunha archipelago, the Falkland Islands/Malvinas, Argentine Tierra del Fuego and Uruguay. The Uruguayan stranding, a subadult male of 4.30 m found on 24 May 2003 on the beach at La Coronilla (33°54' S, Rocha Department) and confirmed by genetic analysis of mitochondrial DNA, is to date the northernmost record of the species in the Atlantic. Some compilations also mention the Kerguelen Islands among the stranding localities.

As regards France, the species is entirely absent from mainland waters: neither the Mediterranean and the Pelagos Sanctuary, nor the Bay of Biscay, nor the English Channel fall within its range, which is exclusively southern. The only possible link with French territory concerns the French Southern and Antarctic Lands, the Kerguelen Islands appearing in certain lists of stranding localities. The available data do not, however, allow the frequency or the status of the species in that area to be established.

Biology and ecology

The ecology of Mesoplodon bowdoini is known only by inference, from carcasses and from what is known of ziphiids in general. Like its congeners, the species is a deep diver that pursues its prey well below the lit zone, in all likelihood beyond 1,000 m depth and during breath-holds that can exceed three quarters of an hour. Hunting is carried out by echolocation and capture by suction: the V-shaped throat grooves make it possible to enlarge the mouth cavity abruptly and draw the prey in, a procedure that makes a true dentition unnecessary. The diet rests on deep-sea squid, supplemented by mesopelagic fish.

Social life remains unknown. The few indications point to small groups of one to six individuals, but no sighting at sea confirms them. The long parallel linear scars borne by adult males do, on the other hand, attest to intraspecific fighting with the tusks, behaviour well documented in mesoplodont beaked whales and generally interpreted as competition for access to females.

Breeding is documented only very indirectly. New Zealand stranding data suggest births from the end of the austral summer into autumn: foetuses have been reported in May and in September, and stranded newborns in May and June. Length at birth is estimated at about 2.2 m. Sexual maturity in males coincides with the eruption of the tusks, at around 3.90 m in total length; study of the Uruguayan specimen made it possible to document this phase of accelerated growth for the first time. Neither the interval between two births, nor the gestation period, nor longevity has been established. Killer whales and large sharks are among the potential predators.

Status and conservation

Andrews' beaked whale is classed as “Data Deficient” (DD) on the IUCN Red List, a status confirmed in the December 2020 update, which covered twenty-two cetaceans. On that occasion, most beaked whales were reclassified as “Least Concern”, but M. bowdoini is among the small group of species for which knowledge remains too patchy to assess a risk of extinction: no abundance estimate exists and the population trend is unknown.

The species has never been the subject of commercial whaling and no bycatch has been formally recorded. The threats identified are therefore those that bear on ziphiids as a whole: underwater noise of human origin, in particular mid-frequency active military sonar, whose link with mass strandings of beaked whales is well established elsewhere in the world; plastic ingestion and chemical contamination, to which predators of deep-sea cephalopods are particularly exposed; the risk of entanglement in drifting fishing gear; and, in the longer term, the redistribution of prey linked to climate change.

In regulatory terms, the species is listed in Appendix II of CITES and benefits from regional protections: the Australian Whale Sanctuary, established by the EPBC Act, covers all Commonwealth waters, and the species falls under the CMS Memorandum of Understanding on Pacific Islands Cetaceans. Strengthening stranding networks and making genetic sampling systematic remain the most effective levers for advancing knowledge.

Observing this species

There is no realistic prospect of observing a living Andrews' beaked whale: more than a century after its description, the species has never been identified with certainty at sea. This invisibility is explained by a combination of factors: a deep and remote oceanic habitat, probably low numbers, discreet behaviour with very little time spent at the surface, a blow that is barely visible and an absence of breaching.

The bulk of what is known therefore comes from the work of stranding networks. Any ziphiid carcass found on a beach in New Zealand, southern Australia or the southern cone of South America constitutes valuable scientific data. The course of action is simple: do not touch or move the animal, keep your distance, report the find immediately to the competent authority or to the local stranding network, and photograph the whole animal as well as the head and the lower jaw in profile, often the only images that allow a determination to species. In mainland France, a stranded cetacean must be reported to the Réseau national échouages; since the species is not present there, a beaked whale seen on French coasts will belong to another species, most often Cuvier's beaked whale (Ziphius cavirostris) or Sowerby's beaked whale (Mesoplodon bidens). In every case, handling a cetacean carcass is reserved for authorised persons, for health reasons as much as scientific ones.

Frequently asked questions

Has an Andrews' beaked whale ever been seen alive?

No. Since its description in 1908, the species has never been identified with certainty alive at sea. All knowledge comes from animals stranded dead, whose total recorded number runs to only a few dozen, which makes it one of the least observed large mammals on the planet.

How large does Andrews' beaked whale grow?

It is a small ziphiid. Precisely measured specimens range from 3.41 to 4.40 m in males and from 3.65 to 4.38 m in females, the largest known female being estimated at 4.87 m. At birth, length is estimated at about 2.2 m. Weight has never been measured reliably; it is estimated at between about 900 and 1,400 kg.

Why do only males have visible teeth?

As in all mesoplodont beaked whales, only adult males have their two mandibular teeth erupt, transformed into flattened tusks that project above the rostrum. These tusks serve in fights between males, as the long white linear scars that streak their bodies attest. In females and young, the teeth remain embedded in the gum.

Can this species be encountered in France?

Not in mainland France: the species is strictly southern and absent from the Mediterranean, the Bay of Biscay and the English Channel. Some compilations mention the Kerguelen Islands, in the French Southern and Antarctic Lands, among the stranding localities, but the available data do not allow its status there to be specified.

How far north does the species range?

Known strandings are distributed between 32° and 54°30' south latitude in the south-west Pacific and the Indian Ocean. In the Atlantic, the synthesis by Baker (2001) gave a range of 36° to 52° south; this northern limit was pushed back to 33°54' S by the stranding of a subadult male on the Uruguayan beach of La Coronilla, on 24 May 2003, an identification confirmed by genetic analysis.

What does the IUCN status “Data Deficient” mean for this species?

This status, confirmed in the December 2020 update, means that the available information allows neither numbers to be estimated nor a trend to be measured, and therefore not the risk of extinction to be assessed. It does not mean that the species is doing well: it reflects an ignorance, which is itself a conservation problem.

Which species might it be confused with?

At sea, with all the other southern mesoplodont beaked whales: Gray's beaked whale, the strap-toothed whale, Hector's beaked whale or the spade-toothed whale. On stranded specimens, the most classic confusion concerns Hubbs's beaked whale (Mesoplodon carlhubbsi) of the North Pacific, whose females and subadults are almost identical; northern hemisphere specimens were thus wrongly attributed to M. bowdoini before being re-identified. The genus Mesoplodon now counts sixteen recognised extant species.

Sources

• https://en.wikipedia.org/wiki/Andrews%27_beaked_whale
• https://fr.wikipedia.org/wiki/Baleine_%C3%A0_bec_d%27Andrews
• https://iucn-csg.org/22-updated-cetacean-red-list-assessments-published-in-december-2020/
• https://us.whales.org/whales-dolphins/species-guide/andrews-beaked-whale/
• https://animaldiversity.org/accounts/Mesoplodon_bowdoini/
• https://www.marinebio.org/species/andrews-beaked-whales/mesoplodon-bowdoini/
• https://seamap.env.duke.edu/species/180513/html
• https://www.lajamjournal.org/index.php/lajam/article/view/219
• https://lajamjournal.org/index.php/lajam/article/download/219/171/171
• https://www.mammaldiversity.org/taxon/1006470/
• https://www.marinespecies.org/rest/AphiaRecordsByName/Mesoplodon%20bowdoini
• https://www.marinespecies.org/rest/AphiaRecordsByName/Hyperoodontidae
• http://id.eaufrance.fr/apt/52688
• https://www.lecerclepolaire.com/baleine-a-bec-d-andrew-2/

Profile compiled from authoritative scientific sources (IUCN, NOAA Fisheries, the specialist literature) and reviewed for factual accuracy.