Perrin's beaked whale

Perrin's beaked whale
Size compared to an average human
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Class: Mammalia
Order: Artiodactyla
Infraorder: Cetacea
Family: Ziphiidae
Subfamily: Hyperoodontinae
Genus: Mesoplodon
Species: M. beaked whale
Binomial name
Mesoplodon beaked whale
Dalebout, Mead, Baker, Baker & van Helden, 2002
Locations and dates of strandings (yellow)
and possible at-sea sightings (dark blue).

Perrin's beaked whale (Mesoplodon perrini) is the newest species of beaked whale to be described. The first two specimens were found in May 1975 stranded on the California coast, with two more specimens being found in 1978 and 1979, and the last in September 1997. They were initially identified as Hector's beaked whale (Mesoplodon hectori), except for the most recent one, which was assumed to be a neonate Cuvier's beaked whale.[2]

Following inclusion of one of these specimens in a mtDNA sequence database of beaked whales, it turned out that they seemed well distinct from M. hectori (Dalebout et al. 1998). The other "Hector's" specimens from California were subsequently confirmed to belong to the same undescribed taxon (Dalebout 2002). The new species was formally described in 2002 by Dalebout et al.; its common and specific names are a tribute to cetologist William F. Perrin.

Despite the superficial similarities to the (entirely allopatric) Hector's beaked whale, this species is closely related to the pygmy beaked whale, the next most-recently described species, and probably represents its Northern Hemisphere sister species.

Perrin's beaked whale has not definitely been recorded alive by scientists. However, its appearance is known from the beached specimens, and following resolution of their identity as a new species, it seems highly likely the four supposed Hector's beaked whales, which were seen off California in 1976 and 1978 (both involving two individuals), were actually this species (Mead 1981, Dalebout et al. 2002).

Description

Perrin's beaked whales cannot be identified with absolute certainty at sea. However, the combination of small size, appearance and presumed range makes a confusion unlikely. Stranded specimens can be identified as this species by either DNA sequence data and/or anatomical details of the skull.(Dalebout et al. 2002)

This species has a fairly typical body shape for a mesoplodont, with a small head, long body, and deep tail. The rostrum of this whale is shorter than every other mesoplodont other than Hector's and the pygmy beaked whales, especially in young individuals. The mouthline of this species is straight, and the melon forms a small bulge with a crescent-shaped blowhole with forward-pointing tips. The teeth on this species are fairly large and towards the tip of the mouth. Throat grooves are present on this species. The mature male specimen was 3.9 metres in length (13 feet) and the female was 4.4 metres (14 feet 8 inches) in length; the immature males measured between 2.1 and 2.45 metres (7-7.5 ft).

The coloration is dark gray above and white below in the holotype male, with a lighter gray underside of the tail fluke. A white patch is present near the navel. The colouration of females is not known, since the only specimen was rather decomposed.

Calves are light to dark gray on top, and white below, including the lower jaw and throat; the underside of the flukes is lighter gray. There is a dark "mask" on the head, from the corners of the mouth to the eye region, the rostrum, and the melon, and there are white stripes on the tail underside. The adult male had the typical white scar-stripes from fights with conspecifics. Only adult males seem to have teeth, and even these only two, in line with other Mesoplodon species. In Perrin's beaked whale, the teeth are located near the tip of the lower jaw and are roughly equilateral triangles when viewed laterally and still placed in the jaw; in this they resemble the foreteeth of Baird's beaked whale more than those of the Mesoplodon species which are otherwise similar.(Dalebout et al. 2002)

A photograph of a possible living specimen - one of the two observed in 1976 - is featured in Rice (1978: 95) as "Mesoplodon carlhubbsi", a distinctly larger species also native to the waters off California. Recordings of the animals' vocalizations were also made on this opportunity.(Mead 1981)

Distribution and status

This species has only been found off the coast of California between San Diego and Monterey. It likely lives offshore the Pacific coast of North America - and possibly elsewhere in the North Pacific - in waters 1,000 meters deep or more. However, evidence is lacking and the northern and southern limits of its range are entirely unknown (though biogeography of beaked whales suggests it does not reach the Equator). No population estimate or assessment of conservation status has hitherto been possible. San Clemente Island holds a sonar research facility of the US Navy; such research has in the past been implicated in causing strandings of cetaceans.

Ecology and behavior

Nothing is known of this species' behavior in life. However, as this is apparently quite similar in all Mesoplodon, a number of well-founded assumptions can be made.

The males of this species seem to engage in fights like most other mesoplodonts. Scars from fighting are present on this species, although the precise mechanism of combat is enigmatic: given the teeth's position near the lower jaw tips, it can be expected that the scars consist of two parallel lines; only single scar lines were present on the adult male, however, suggesting glancing blows rather than direct attacks created them.

Few stomach contents were available for analysis. Presumably, this species eats pelagic squid (such as Octopoteuthis deletron, remains of which were found in the female's stomach) and possibly small fish[3] like other beaked whales.

The largest immature LACM 088901, at 2.45 metres of length, was apparently independent from its mother. On the other hand, the smallest known specimen, USNM 504259, had a fringed tongue which indicated it was still suckling. Teeth were not present in the immatures, but they are not needed for feeding. The dates when the specimens were found suggest the young start to feed independently in summer; considering most whales suckle until around one year of age, this suggests the young are born during the summer half of the year. Consequently, as they are all of somewhat similar size, the immatures were probably around one year old. The adults were both an estimated 9 years old when they died.

The causes of death of two animals can be tentatively inferred; the 1997 specimen was starving at the time of death, possibly following a parasite infection (Dalebout et al. 2002). The 1975 female had died around May 14 (Mead 1981); given that the juvenile found on May 22 was apparently its calf and that it was not yet fully weaned, its death seems to be a direct consequence of the loss of its mother.

As with their relatives, cookiecutter sharks attack this whale to try and bite off chunks of flesh. Such attacks are generally not life-threatening to the whale. It is a host of the thoracican barnacle Conchoderma auritum, and for one or several species of parasitic Phyllobothrium cestodes (possibly Phyllobothrium delphini), this species is either a primary or a dead-end host.

Specimens

  1. USNM 504259 - May 22, 1975; 33°15′N 117°26′W / 33.250°N 117.433°W / 33.250; -117.433 - the smallest specimen, an immature male
  2. USNM504260 - May 28, 1975; 33°16′N 117°26′W / 33.267°N 117.433°W / 33.267; -117.433 - an adult, the only female known to date and probably the mother of USNM 504259 (Dalebout et al. 2002)
  3. USNM504853 - September 9, 1978; 33°07′N 117°20′W / 33.117°N 117.333°W / 33.117; -117.333 - an adult male, the holotype
  4. LACM 088901 JRH 052 - December 27, 1979; 32°55′N 117°15′W / 32.917°N 117.250°W / 32.917; -117.250 - an immature male
  5. TMMC-C75 - September 18, 1997; 36°37′N 121°55′W / 36.617°N 121.917°W / 36.617; -121.917 - an immature male

The 1976 possible sightings took place on July 30, the 1978 one on September 9 - the same day the holotype specimen was discovered (Mead 1981). Altogether, there is a marked concentration of sightings between May and September. It is unknown if this has any significance. Nonetheless, with the scant data at hand, it still appears that looking for small beaked whales during the summer months in the area between Santa Catalina and San Clemente Islands and the mainland has the best odds of encountering this enigmatic species.

References

Footnotes

  1. ↑ Taylor, B.L.; Baird, R.; Barlow, J.; Dawson, S.M.; Ford, J.; Mead, J.G.; Notarbartolo di Sciara, G.; Wade, P. & Pitman, R.L. (2008). "Mesoplodon perrini". IUCN Red List of Threatened Species. Version 2008. International Union for Conservation of Nature. Retrieved 24 March 2009. Database entry includes a brief justification of why this species is of data deficient.
  2. ↑ These specimens provided data which erroneously has been published as referring to M. hectori, before their true identity became known – especially since the adult male of Hector's Beaked Whale has only recently been described. Dalebout et al. (2002) specifically list Mead (1981), Mead (1984), Mead & Baker (1987), Mead (1989), Baker (1990), Jefferson et al. (1993), Mead (1993), Carwardine (1995), Reeves & Leatherwood (1994), Henshaw et al. (1997) and Messenger & McQuire (1998)
  3. ↑ Note that the supposed unidentifiable "vertebrate" piece discovered in the female specimen's stomach is probably a misprint; the original description of the specimen (Mead 1981) has "invertebrate".
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