Hourglass Dolphin
Encyclopedia
The hourglass dolphin (Lagenorhynchus cruciger) is a small dolphin
in the family
Delphinidae that inhabits Antarctic
and sub-Antarctic waters.
The dolphin has rarely been seen. It was identified as a new species
by Qouy and Galmard in 1824 from a drawing made in the South Pacific
in 1820. It is the only cetacean to have been widely accepted as a species solely on witness accounts. By 1960, despite decades of whaling
in the Southern Ocean
, only three specimens had been recovered. As of 2010 only 6 complete and 14 partial specimens had been examined. Further information was obtained from 4 strandings and boats which searched for the dolphins in areas rarely visited by ships.
Though it is 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
.
for "cross-carrier". This refers to the area of black coloration, 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 lives as far south. The right whale dolphin does not have a dorsal fin
, so the two species are easily distinguished. The fin considerably varies across individuals. It is generally tall and curved, and the curve may be particularly pronounced in older animals.
A fully grown adult is about 1.8 metres (5.9 ft) length and weighs 90–120 kg (198.4–264.6 ). Males are thought to be slightly smaller and lighter than females, although the small number of specimens does not permit a firm conclusion.
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 the population size at more than 140,000 individuals.
study recorded a group of 60.
They share feeding grounds with other cetaceans such as sei
, pilot
, bottlenose
and minke whale
s and southern right whale dolphin
s. They are regularly seen with fin whale
s. Whalers who were hunting these much larger animals used hourglass dolphins as "look-outs" to aid them in their hunt. Hourglass dolphins are keen bow-wave riders.
Examinations of the stomach contents of the few specimens indicate they eat various (unrecorded) types of squid
and small fish.
Dolphin
Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...
in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Delphinidae that inhabits Antarctic
Antarctic
The Antarctic is the region around the Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica and the ice shelves, waters and island territories in the Southern Ocean situated south of the Antarctic Convergence...
and sub-Antarctic waters.
The dolphin has rarely been seen. It was identified as a new species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
by Qouy and Galmard in 1824 from a drawing made in the South Pacific
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
in 1820. It is the only cetacean to have been widely accepted as a species solely on witness accounts. By 1960, despite decades of whaling
Whaling
Whaling is the hunting of whales mainly for meat and oil. Its earliest forms date to at least 3000 BC. Various coastal communities have long histories of sustenance whaling and harvesting beached whales...
in the Southern Ocean
Southern Ocean
The Southern Ocean comprises the southernmost waters of the World Ocean, generally taken to be south of 60°S latitude and encircling Antarctica. It is usually regarded as the fourth-largest of the five principal oceanic divisions...
, only three specimens had been recovered. As of 2010 only 6 complete and 14 partial specimens had been examined. Further information was obtained from 4 strandings and boats which searched for the dolphins in areas rarely visited by ships.
Though it is traditionally placed in the genus Lagenorhynchus
Lagenorhynchus
Lagenorhynchus is a genus in the order Cetacea, traditionally containing six species:* white-beaked dolphin, Lagenorhynchus albirostris* Atlantic white-sided dolphin, Lagenorhynchus acutus...
, recent molecular
Molecular phylogeny
Molecular phylogenetics is the analysis of hereditary molecular differences, mainly in DNA sequences, to gain information on an organism's evolutionary relationships. The result of a molecular phylogenetic analysis is expressed in a phylogenetic tree...
analyses indicate that the hourglass dolphin is actually more closely related to the dolphins of the genus Cephalorhynchus
Cephalorhynchus
Cephalorhynchus is a genus in the dolphin family Delphinidae. It consists of four species:*Commerson's Dolphin, Cephalorhyncus commersonii*Chilean Dolphin, Cephalorhyncus eutropia*Heaviside's Dolphin, Cephalorhyncus heavisidii...
.
Physical description
The hourglass dolphin is colored black and white and for this reason was colloquially known by whalers as a "sea cow". Each flank has a white patch at the front, above the beak, eye and flipper, and a second patch at the rear. These two patches are connected by a thin white strip, creating, loosely speaking, an hourglass shape and hence the common name of the dolphin. The scientific name cruciger is LatinLatin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
for "cross-carrier". This refers to the area of black coloration, which, viewed from above, vaguely resembles a Maltese cross
Maltese cross
The Maltese cross, also known as the Amalfi cross, is identified as the symbol of an order of Christian warriors known as the Knights Hospitaller or Knights of Malta and through them came to be identified with the Mediterranean island of Malta and is one of the National symbols of Malta...
or cross pattée
Cross pattée
A cross pattée is a type of cross which has arms narrow at the centre, and broader at the perimeter. An early English example from the start of the age of heraldry proper A cross pattée (or "cross patty", known also as "cross formée/formy") is a type of cross which has arms narrow at the...
.
In its usual range the dolphin is easily identifiable. Only the southern right whale dolphin
Southern Right Whale Dolphin
The southern right whale dolphin, Lissodelphis peronii, is a small and slender species of mammal found in cool waters of the southern hemisphere...
is of comparable size and lives as far south. The right whale dolphin does not have a dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
, so the two species are easily distinguished. The fin considerably varies across individuals. It is generally tall and curved, and the curve may be particularly pronounced in older animals.
A fully grown adult is about 1.8 metres (5.9 ft) length and weighs 90–120 kg (198.4–264.6 ). Males are thought to be slightly smaller and lighter than females, although the small number of specimens does not permit a firm conclusion.
Population and distribution
The range is circumpolarCircumpolar
The term circumpolar may refer to:* circumpolar navigation: to travel the world "vertically" traversing both of the poles* Antarctic region** Antarctic Circle** the Antarctic Circumpolar Current** Subantarctic** List of Antarctic and subantarctic islands...
from close to the Antarctic ice pack to about 45°S. The most northerly confirmed sightings were 36°S in the South Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
and 33°S near Valparaíso
Valparaíso
Valparaíso is a city and commune of Chile, center of its third largest conurbation and one of the country's most important seaports and an increasing cultural center in the Southwest Pacific hemisphere. The city is the capital of the Valparaíso Province and the Valparaíso Region...
, Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
, in the Pacific. Sightings have been made most commonly from the south of New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, around the South Shetland Islands
South Shetland Islands
The South Shetland Islands are a group of Antarctic islands, lying about north of the Antarctic Peninsula, with a total area of . By the Antarctic Treaty of 1959, the Islands' sovereignty is neither recognized nor disputed by the signatories and they are free for use by any signatory for...
and off Tierra del Fuego
Tierra del Fuego
Tierra del Fuego is an archipelago off the southernmost tip of the South American mainland, across the Strait of Magellan. The archipelago consists of a main island Isla Grande de Tierra del Fuego divided between Chile and Argentina with an area of , and a group of smaller islands including Cape...
, Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
. The species is unlikely to be particularly densely populated close to these lands.
One survey estimated the population size at more than 140,000 individuals.
Behavior
Hourglass dolphins tend to move in groups of about 5 to 10. One International Whaling CommissionInternational Whaling Commission
The International Whaling Commission is an international body set up by the terms of the International Convention for the Regulation of Whaling , which was signed in Washington, D.C...
study recorded a group of 60.
They share feeding grounds with other cetaceans such as sei
Sei Whale
The sei whale , Balaenoptera borealis, is a baleen whale, the third-largest rorqual after the blue whale and the fin whale. It inhabits most oceans and adjoining seas, and prefers deep offshore waters. It avoids polar and tropical waters and semi-enclosed bodies of water...
, pilot
Pilot whale
Pilot whales are cetaceans belonging to the genus Globicephala. There are two extant species, the long-finned pilot whale and the short-finned pilot whale . The two are not readily distinguished at sea and analysis of the skulls is the best way to tell the difference between them...
, bottlenose
Bottlenose whale
The Northern bottlenose whale is a species of the ziphiid family, one of two members of the Hyperoodon genus. The northern bottlenose was hunted heavily by Norway and Britain in the 19th and early 20th centuries...
and minke whale
Minke Whale
Minke whale , or lesser rorqual, is a name given to two species of marine mammal belonging to a clade within the suborder of baleen whales. The minke whale was given its official designation by Lacepède in 1804, who described a dwarf form of Balænoptera acuto-rostrata...
s and southern right whale dolphin
Southern Right Whale Dolphin
The southern right whale dolphin, Lissodelphis peronii, is a small and slender species of mammal found in cool waters of the southern hemisphere...
s. They are regularly seen with fin whale
Fin Whale
The fin whale , also called the finback whale, razorback, or common rorqual, is a marine mammal belonging to the suborder of baleen whales. It is the second longest whale and the sixth largest living animal after the blue whale, bowhead whale, and right whales, growing to nearly 27 metres long...
s. Whalers who were hunting these much larger animals used hourglass dolphins as "look-outs" to aid them in their hunt. Hourglass dolphins are keen bow-wave riders.
Examinations of the stomach contents of the few specimens indicate they eat various (unrecorded) types of squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
and small fish.