Blainville's beaked whale

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Blainville's beaked whale. Source: Chelonia Limited

Blainville's Beaked Whale (also known as the Dense-beak whale; scientific name: Mesoplodon densirostris) is one of 21 species of beaked whales (Hyperoodontidae or Ziphiidae), 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.

A particularly easy species to identify, Blainville's beaked whale has two distinctive horn-like teeth that grow from bulges in the lower jaw, and may be encrusted with barnacles. The forehead is flattened and the lower jaw is arched, giving the head a similar appearance to the right whale. Blainville's beaked whale is dark blue-grey above, and light below, with a darker dorsal fin and eye patch. Females develop white upper and lower jaws, and both sexes have large white spots covering the entire body. Males are heavily and deeply scarred from fighting, as well as from attacks by the Cookie-cutter shark, which leaves characteristic marks.

Beakedwhale blainvilles-ari friedlaender duke.jpg Blainville's Beaked Whale. Source: Ari Friedlaender, Duke University/NOAA
524px-blainville-s beaked whale size.png Size comparison of an average human against Blainville's 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 densirostris (Blainville, 1817)

Common Names:
Atlantic beaked whale
Baleine
Blainville's beaked whale

Blainvilles beaked whale is found worldwide in warm temperate to tropical waters. Small pods of three to seven whales have been seen off Hawaii in waters 700 to 1000 meters deep, near much deeper water. None have been seen near the British Isles, but one was recorded from Portugal and one from the Mediterranean coast near Spain. There are also scattered records from the Indian Ocean, the South Atlantic, and the South Pacific. Males of this species have relatively enormous teeth, about 120 millimeters (mm) high, 80 mm deep from front to back, and 30 mm wide. Their mouths have a distinctively curved line, as the lower jaw becomes very deep toward the back to accommodate them. A female stranded in North Carolina had scars on her skin that might have come from a Killer whale or False killer whale.

Found in groups of three to seven, Blainville's beaked whale both avoids and approaches boats. It performs shallow dives, as well as deeper dives lasting up to 45 minutes. On surfacing, the beak appears first, pointing vertically upwards, and after taking a breath, the beak is slapped against the water surface. The whale has also been noted as rolling slightly before diving. It feeds on fish and squid, locating its prey by echolocation. Little is known of its reproductive biology, although calves have been seen in spring.

Physical Description

Overview species physical features are: endothermic metabolism; homoiothermic; and bilateral symmetry. Head and body combined length ranges from three to seven meters, and adult body mass may slightly exceed 1000 kilograms. Pectoral fin length measures 20 to 70 centimeters (cm), dorsal fin height measures 15 to 20 cm, and tail fluke width is approximately 100 cm. Color varies from silver-gray to brown above and light gray to white below. The body is marked with scars and sctratches. Juveniles are lighter in color.

There is a clear sexual dimorphism in this species, chiefly manifesting in differing shapes of the two sexes. Two large teeth protrude from the middle of the mandible in males. These teeth point upward above the head of the whale, and they are often sheathed with a layer of barnacles. The other teeth are poorly developed and non-functional. The mouths of the female and young are slightly upcurved.

Behavior

Key behaviors are: natatorial; motile; solitary; and social. This mammal is able to remain underwater for 10 to 40 minutes, breathing only a few times before diving again. Cetaceans of this species can be identified in the water by their characteristic surfacing behavior; they thrust the chin and snout out of the water, and then rock the head back into the water as the the back and dorsal fin surface. Members of this genus usually travel alone or in small groups.

Lifespan

Females live at least 27 years (Ronald Nowak 1999), but probably much longer. As such, maximum longevity in this species must be classified as unknown.

Distribution and Movements

File:Distribution of Blainville

This species has a world-wide distribution, found broadly throughout the temperate and tropical marine Northern and Southern Hemisphere seas.

Habitat

Mesoplodon densirostris is found in both temperate and tropical waters. These animals seem to prefer to travel in deep waters, and are most common in Hawaii, where the ocean reaches depths of 1000 fathoms.

Feeding Habits

Blainville's beaked whale feeds in deep waters, preying on fish, mollusks and squid.

Threats and Conservation Status

The threats to Blainville's beaked whale are poorly understood, but it is known to be susceptible to high intensity, low frequency, active sonar used by US and NATO vessels. This brings about acoustic trauma and results in strandings, thought to be caused by surfacing too quickly. It is also at risk from the ingestion of rubbish, as well as incidental catch and low levels of hunting.

The IUCN Red List adds:

Some Blainville's beaked whales have been taken incidentally by Japanese tuna boats off the Seychelles and Western Australia, as well as directly by small cetacean hunters in various areas. Dolar (1994) investigated directed fisheries for marine mammals in central and southern Visayas, northern Mindanao and Palawan, Philippines from archived reports and visits to sites where such fisheries are conducted. Hunters at Pamilacan Island take some small whales, including Mesoplodon densirostris. Dolphins and whales are taken by hand harpoons or, increasingly, by togglehead harpoon shafts shot from modified, rubber-powered spear guns. Jefferson et al. (1993) reported that some specimens have been incidentally taken in the North Pacific by Taiwanese fishermen, and accidentally by Japanese tuna fishermen in the Indian Ocean.

In 1993, an adult Blainville's beaked whale was found washed ashore in southern Brazil (Secchi and Zarzur 1999). Stomach analysis revealed the presence of a bluish bundle of plastic threads occupying a large part of the main stomach chamber. Both stomach and intestines were completely free of parasites, as well as food remains and faeces, indicating that the whale had not fed for some time. The ingested plastic may have resulted in a false sensation of satiation for the animal, which could have reduced the whale's appetite and meal size and, in turn, led to the death of the whale. This form of water pollution may be increasing and could be a threat to the species.

In recent years, there has been increasing concern that loud underwater sounds, such as active sonar and seismic operations, may be harmful to beaked whales (Malakoff 2002). The use of active sonar from military vessels has been implicated in mass strandings of Blainville’s beaked whales (Balcomb and Claridge 2001, Jepson et al. 2003; Wang and Yang 2006; Yang et al. 2008). A stranding of two Cuvier’s beaked whales in the Gulf of California was also closely correlated with a seismic survey (Malakoff 2002). The mechanistic cause of the strandings is not well understood, but gas bubble formation (Fernandez et al. 2005) from a behaviorally mediated response to sound has been proposed (Cox et al. 2006).

Blainville's beaked whale is classified as Data Deficient (DD) on the IUCN Red List 2004 and is listed on Appendix II of CITES. It is also listed on Appendix II of the Berne Convention on the Conservation of European Wildlife and Natural Habitat, on Annex IV of the EC Habitats Directive and on Schedule II of the Indian Wildlife Protection Act 1972.

No conservation action has been targeted specifically at this species, but its inclusion on the Berne Convention, the EC Habitats Directive and CITES (Convention on International Trade in Endangered Species of Flora and Fauna) give it some protection. Further research into the distribution and population of this distinctive species is necessary before an action plan can be drawn up.

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Citation

Encyclopedia of Life (2011). Blainville's 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/Blainville's_beaked_whale
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