See text The mesoplodont whales are the fourteen species of whale that make up the genus Mesoplodon, making it the single largest genus in the cetacean order. Two species were discovered for the first time as recently as 1991 and 1995, and many marine biologists expect to discover more species in the future. This genus is traditionally characterized by the size and shape of the skull, in particular the distinctive curved beak shape at the jaw, shaped rather like a playground slide. Some other whale species share this property and together they are known as the beaked whales. The word mesoplodon comes from the Greek meso- (middle) - hopla (arms) - odon teeth, and may be translated as 'armed with a tooth in the centre of the jaw'.

The species

English name (most common first), Latin name, known distribution:

• Andrew's Beaked Whale, Deep-crested Beaked Whale, M. bowdoini, unknown, possibly circumpolar on latitudes roughly level with New Zealand
• Bahamonde's Beaked Whale, M. bahamondi, unknown, one individual found off Chile
• Blainville's Beaked Whale, Dense Beaked Whale, M. densirostris, circumpolar temperate waters
• Gervais' Beaked Whale, Antillean Beaked Whale, Gulf Stream Beaked Whale, M. europaeus, temperate to tropical North Atlantic Ocean, Caribbean Sea
• Ginkgo-toothed Whale, Japanese Beaked Whale, M. ginkgodens, tropical Indian and Pacific Oceans
• Gray's Beaked Whales, Haast's Beaked Whale, M. grayi, circumpolar temperate Southern Hemisphere.
• Hector's Beaked Whale, New Zealand Beaked Whale, M. hectori, circumpolar cool-to-temperate Southern Hemisphere waters
• Hubbs' Beaked Whale, M. carlhubbsi, temperate North Pacific
• Layard's Beaked Whale, Long-toothed Beaked Whale, Strap-toothed Whale, M. layardii, circumpolar Southern Ocean
• Perrin's Beaked Whale, M. perrini, eastern Pacific
• Pygmy Beaked Whale, Peruvian Beaked Whale, Lesser Beaked Whale, M. peruvianus, off west coast of South America
• Sowerby's Beaked Whale, North Atlantic Beaked Whale, M. bidens, North Atlantic Ocean
• Stejneger's Beaked Whale, Bering Sea Beaked Whale, M. stejnegeri, Cool to sub-Arctic Pacific Ocean, Bering Sea
• True's Beaked Whale, M. mirus, North Atlantic Ocean, possibly southern Indian Ocean
• Unidentified Beaked Whale, M. sp. 'A' , known only from sightings in the Eastern Tropical Pacific Ocean

Longman's Beaked Whale (also known as the Indo-Pacific Beaked Whale) is also sometimes classed in the Mesoplodon genus. However most authorities follow the lead of Joesph Curtis Moore who in the 1960s put it in its own genus - the Indopacetus.

Physical description and behaviour

Physical data is scant for almost all species on account of the fact that mesoplodons all live far out to sea. For instance it is not known whether females are larger than males. From beached individuals we know that the whales are small, ranged from 4-6m in length and are typically about one 1000-1500kg in weight.

Species typically have a small triangular dorsal fin about two-thirds to three-quarters along the back.

Virtually nothing is known about mesoplodon behaviour as so few have been seen alive. Further their range of behaviours at the surface appears limited to slow swimming. There is usually no surface blow and there have been no reports of a mesoplodon fluking (raising their tail fluke clear of the water on diving).

Longeveity, lactation and gestation data is non-existent.

Conservation

The mesoplodon species populations are unknown and consequently the species are generally omitted from Red Data Species lists. The main threat from humans is the accidental capture in drift nets.