Gervais' beaked whale

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Gervais' beaked whale. Source. MarineBio

Gervais' beaked whale (scientific name: Mesoplodon europaeus) is is one of 21 species of beaked whales (Hyperoodontidae or Ziphiidae), all of which are medium-sized whales with distinctive, long and narrow beaks and dorsal fins set far back on their bodies. They are marine mammals within the order of cetaceans.

20433 mesoplodon-europaeus.jpg Gervais' beaked whale. Source: Collection Georges Declercq
472px-gervais- beaked whale size.png Size comparison of an average human against Gervais' beaked whale. Source: Chris Huh

Conservation Status:
Data Deficient

Scientific Classification

Kingdom: Animalia
Phylum:--- Chordata
Class:------ Mammalia
Order:-------- Cetacea
Family:-------- Hyperoodontidae
Genus:--------- Mesoplodon
Species:--------Mesoplodon europaeus (Gervais, 1855)

Common Names:
Antillean Beaked Whale
Atlantic Beaked Whale
Dense Beaked Whale
European beaked whale
Gervais' beaked whale
Gulf Stream beaked whale
Gervais's beaked whale

Gervais' beaked whale is a small beaked whale that can reach up to 5.5 m in length. The lower jaw has a single pair of teeth (exposed only in adult males). The forehead rises at a shallow angle. It has a distinct beak and the mouthline is curved down at rear. Gervais' beaked whale has a charcoal grey dorsal and lateral colouration with a lighter belly.

Adults may have clear scratches and scars on the body.Gervais' beaked whale may be confused with True's beaked whale but it has conspicuously smaller flippers. Gervais' beaked whales are usually found either alone or in small groups.

Gervais' beaked whale has a prominent, slender beak with only two teeth which, whilst obvious in males, are not visible in females. These whales are dark grey to black on the back, fading to light grey or white on the underside. The head is relatively small with a slightly bulging forehead and the dorsal fin is situated towards the tail end of the back.

Physical Description

Gervais' beaked whale is nearly impossible to distinguish from other beaked whales when sighted at sea. Overview physical beatures as for other beaked whales are endothermic metabolism and bilateral symmetry. Females are thought to be larger than males, becoming sexually mature at 4.5 meters (m) and giving birth to highly dependent young of just 2.1 m. Adult lengths are approximately 5.2 m for females and 4.6 m for males. Six whales have been weighed, and the body masses ranged from 49 kilograms (kg) for a 1.62 metre-long calf to 1178 kg for a female that was 3.71 metres in length.

Gervais' beaked whale is a toothed whale and can be recognised as such by the single blowhole and the presence of teeth (rather than baleen). It is a member of the beaked whale family with the characteristic V-shaped crease on the throat and the short dorsal fin set relatively far back.

The colouration of Gervais' beaked whale is black or dark grey on the back fading to a lighter gray on the sides and belly; juveniles' bellies are white. For a cetacean, the head is relatively small with respect to total body size.

The tails of ziphiids (beaked whales) are unusual among cetaceans in having no notch in the center of the fluke. Some stranded specimens, particularly adult males, have many scars on their bodies, presumably from sharks and fighting between males.

Nearly all ziphiids have a greatly reduced number of teeth, and Gervais' beaked whale has only two in the lower jaw. These two teeth are are visible outside the mouth as small tusks near the front of the rostrum. Conchoderma, or stalked barnacles, often attach themselves to these teeth. Tusk shape varies between species and it has been proposed that these difference evolved in order to aid the animals in differentiating their own species, as Mesoplodon species are otherwise very similar in appearance. It is extremely difficult to distinguish the similar-looking species of this genus by sightings, and sometimes even when using the diagnostic characters of the skull. (Lynn and Ross, 1992; Martin et al, 1990; McLeod, 2000b; Robineau and Vely, 1993; Vaughn et al, 2000; Pitman, 2001) The stomach, which has unexplained multiple chambers, has been found to contain mainly squid, in addition to deep sea shrimp and viper fish.

Behaviour

Key general species behaviours are motile and social. Very little detail is known about the species behaviour and dive duration, due to the relative lack of sightings (Kinze, 2002). They are thought to live in couples or small groups, and fighting between males is assumed to occur as stranded males are highly scarred. However, the distinctive tooth marks of the Cookie-cutter shark and the orca have been seen on individuals as well. (The Azorean Whale Watching Base, 2000; Debrot and Barros, 1992)

More than 50 Gervais’s beaked whales have been found stranded along the coast of the United States. The holotype of this species (the individual that was identified as a separate species, and named) was found floating in the English Channel in about 1840, and the name europeaus was applied, but since then, only one more has been reported from European waters. The whales apparently live in deep tropical to warm temperate waters of the Atlantic Ocean. As with other species in this genus, little is known about them.

Lifespan

One specimen may have been over 48 years old (Ronald Nowak 2003), and this is the maximum recorded age in the wild.

Reproduction

Key general reproductive features are: gonochoric/gonochoristic/dioecious (sexes separate); viviparous. Very little detailed reproductive information is available, but females are thought to be sexually mature by the time they reach 4.5 metres size. (Martin et al, 1990; Poss, 1998; Pitman, 2001) As with all cetaceans, the young are necessarily precocial at birth and Mesoplodon europaeus are about 2.1 metres long at birth.

Distribution and Movements

File:Distribution of Gervais

Gervais' beaked whale is known only from strandings, so the known distribution may be affected by ocean currents and efforts in North America to retrieve stranded animals. Recorded from as far north as New York and as far south as Trinidad, Mesoplodon europaeus is probably the most abundant member of its genus in the Gulf of Mexico. Records from the eastern side of the Atlantic are more spotty, ranging from Ireland to Guinea Bissau in Africa. A relationship has been suggested between water temperatureand prey species distribution, thus affecting the distribution of different Mesoplodon species. (McLeod, 2000a; Robineau and Vely, 1993)

Habitat

Gervais' beaked whale is an oceanic and coastal species that may be seen at the surface, but little is known as to the depths of their dives.

Feeding Habits

From stomach contents of stranded Gervais' beaked whale it is known that they consume primarily squid (Octopoteuthis spp., Mastigoteuthis spp. and Taonius spp.), deep sea shrimp (Gnathophausia ingens) and mesopelagic viper fish (Chauliodus sloani and Nesiarchus nasutus); mollusks are also known to be taken. The stomach is divided into multiple chambers. The purpose of this is undetermined, as squid and fish are easily digested, as opposed to the tough material eaten by most animals with such stomach morphology. (Vaughn et al, 2000; Debrot and Barros, 1992; Martin et al, 1990)

Predation

From distinctive scars on some stranded beaked whale specimens it is known that cookie-cutter sharks do attack Mesoplodon europaeus. The whale probably uses its tusks to protect itself from this and other predators, as well as for interspecific fighting. (Pitman, 2001)

Threats and Conservation Status

The main threats to Gervais' beaked whale are accidental entanglement in gillnets and acoustic trauma following military noise pollution underwater.

In the mid to late 1980s, several mass strandings were thought to be associated with naval activities around the Canary Islands. Later, between 1992 and 1998, 28 Gervais' beaked whales were stranded along the US coast between Florida and Massachusetts, followed by more mass strandings in September 2002 after NATO tested low frequency sonar.

The IUCN Red List add:

This species, like other beaked whales, is likely to be vulnerable to loud anthropogenic sounds, such as those generated by navy sonar and seismic exploration (Cox et al. 2006).

In particular, several atypical mass strandings of beaked whales, including Gervais' beaked whales, were associated with naval activities: mid to late 1980s on the Canary Islands (Waring et al. 2006), in March 2000 on the Bahamas (Rowles et al. 2000, Anonymous 2001) and again in September 2002 during a naval NATO manoeuvre involving low frequency sonar around the Canaries (Vidal pers. comm.).

Evidence from stranded individuals of several species, including Mesoplodon europaeus, indicates that they have swallowed discarded plastic items, which may eventually lead to death (e.g. Scott et al. 2001).

Direct hunting has never been associated with this species. Pervasive gillnet and longline fisheries throughout the species' range raises concern that some bycatch is likely. Even low levels of bycatch might cause unsustainable impacts on this group of naturally rare cetaceans.

Gervais' beaked whale is classified as Data Deficient (DD) on the IUCN Red List 2004, and is listed on Appendix II of CITES.

All cetaceans (whales and dolphins) are listed on Annex A of EU Council Regulation 338/97; they are therefore treated by the EU as if they are included in CITES Appendix I, so that commercial trade is prohibited. There are no special conservation plans for this species, although trade in this species is limited by CITES around the world and prohibited in Europe.

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Citation

Encyclopedia of Life. (2011). Gervais' beaked whale. ed. C. Michael Hogan. Encyclopedia of Earth. National Council for Science and Environment. Washington DC. Retrieved from http://editors.eol.org/eoearth/wiki/Gervais'_beaked_whale
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