Everything about The Hourglass Dolphin totally explained
The
Hourglass Dolphin (
Lagenorynchus cruciger) is a small
dolphin found in
Antarctic and sub-Antarctic waters.
The dolphin was for a long time rarely seen. It was first identified as a new species by Qouy and Galmard in
1824 from a drawing made in the
South Pacific in 1820. It is only the
cetacean to have been widely accepted as a species on eye accounts alone
1. Indeed by
1960, despite decades of
whaling in the
Southern Ocean, only three specimens had been brought to the attention of
scientists. Even now only 6 complete and 14 partial specimens have been examined. Further information has been obtained from 4 strandings and boats which have deliberately set out to observe the dolphins in areas rarely otherwise visited by ships.
Though it's traditionally placed in the genus
Lagenorhynchus, recent
molecular analyses indicate that the Hourglass Dolphin is actually more closely related to the dolphins of the genus
Cephalorhynchus and ought to be placed in that genus.
Physical description
The Hourglass Dolphin is coloured black and white and for this reason was colloquially known by whalers as the "sea
cow". On each flank there's a white patch at the front of the dolphin, above the beak, eye and flipper, and a second patch at the rear. These two patches are connected by a thin strip of white, creating, loosely speaking, an
hourglass shape and hence the common name of the dolphin. The scientific name
cruciger is
Latin for "cross-carrier". This refers to the area of black colouration on the body, which, viewed from above, vaguely resembles a
Maltese cross or
cross pattée.
In its usual range the dolphin is easily identifiable. Only the
Southern Right Whale Dolphin is of comparable size and found so far south. The Right Whale Dolphin doesn't have a
dorsal fin and so the two species are trivially distinguished from one another. The fin varies from one individual to another quite considerably. Broadly speaking it's tall and curved, and the curve may be particularly pronounced in older animals.
A fully grown adult is about 1.8 m in length and weighs 90-120 kg. Males are probably slightly smaller and lighter than females (from a sample size of eight specimens).
Population and distribution
The range is
circumpolar from close to the Antarctic ice pack to about 45°S. The most northerly confirmed sightings were 36°S in the South
Atlantic Ocean and 33°S near
Valparaíso,
Chile, in the
Pacific. Sightings have been made most commonly from the south of
New Zealand around the
South Shetland Islands and off
Tierra del Fuego,
Argentina. The species is unlikely to be particularly densely populated close to these lands. One survey estimated that there was a minimum of 140,000 individuals alive today.
Behaviour
Hourglass Dolphins tend to move in groups of about 5-10 in number. One
International Whaling Commission study recorded a group of 60. They share feeding grounds with other cetaceans such as
Sei,
Pilot,
Bottlenose and
Minke Whales and
Southern Right Whale Dolphins. They are found very regularly with
Fin Whales. In fact whalers hunting these much larger whales used Hourglass Dolphins as "look-outs" to aid them in their hunt. Hourglass Dolphins are keen bow-riders.
Examinations of the stomach contents of the few analysed specimens indicated the it eats various (unrecorded) types of
squid and small fish.
Image:hourglass dolphin.jpg|Two hourglass dolphins breaching
Image:hourglass dolphin 2.jpg|The hourglass dolphin has a beautiful and striking black-and-white pattern.
Further Information
Get more info on 'Hourglass Dolphin'.
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