Dwarf Sperm Whale
Encyclopedia
The Dwarf Sperm Whale is one of three species
in the sperm whale family
. They are not often sighted at sea. As such, most information is a result of the study of stranded carcasses.
, in the Kogiidae family and Kogia genus, however it was not until 1966 that the two species were regarded as separate, and even more recently that Kogiidae was regarded as a subfamily (Kogiinae) of Physeteridae.
s. The species makes slow, deliberate movements with little splash or blow and usually lies motionless when at the sea's surface. Consequently it can be observed only in very calm seas.
The Dwarf Sperm Whale is similar in appearance and behavior to its cousin the Pygmy Sperm Whale
. Identification may be close to impossible at sea – however, the Dwarf is slightly smaller and has a larger dorsal fin
. The body is mainly bluish gray with a lighter underside with slightly yellow vein
-like streaks possibly visible. There is a white false gill
behind each eye. The flippers are very short and broad. The top of the snout
overhangs the lower jaw
, which is small. Dwarfs have long, curved and sharp teeth (0–6 in the upper jaw, between 14 and 26 in the lower). These teeth led to the species being described as the "rat
porpoise
" in the Lower Antilles
.
Like other Sperm Whales, the Dwarf Sperm Whale has a spermaceti
organ in its forehead. Like the pygmy, the dwarf is able to expel a dark reddish substance when frightened or attacked—possibly to put off any predators.
Dwarf sperm whales are usually solitary but have occasionally been seen in small groups. They feed mainly on squid
and crab
.
. In the Atlantic, strandings have been observed in Virginia
, United States
in the west and Spain
, United Kingdom
in the east, and as far south as southern Brazil
and the tip of Africa
. In the Indian Ocean
, specimens have been found on the south coast of Australia
and on many places along the Indian Ocean's northern coast - from South Africa
right round to Indonesia
. In the Pacific, the known range includes the Japan
ese coast and British Columbia
. No global population estimates have been made. One survey estimated a population of about 11,000 in the eastern Pacific.
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...
in the sperm whale family
Sperm whale family
Physeteroidea is a superfamily including just three living species of whale; the Sperm Whale, in the genus Physeter, and the Pygmy Sperm Whale and Dwarf Sperm Whale, in the genus Kogia...
. They are not often sighted at sea. As such, most information is a result of the study of stranded carcasses.
Taxonomy
Today, the dwarf sperm whale is generally classified as one of two species, along with the Pygmy Sperm WhalePygmy Sperm Whale
The Pygmy Sperm Whale is one of three species of toothed whale in the sperm whale family. They are not often sighted at sea, and most of what is known about them comes from the examination of stranded specimens.-Taxonomy:...
, in the Kogiidae family and Kogia genus, however it was not until 1966 that the two species were regarded as separate, and even more recently that Kogiidae was regarded as a subfamily (Kogiinae) of Physeteridae.
Physical description
The Dwarf Sperm Whale is the smallest species commonly known as a whale. It grows up to 2.7 metres (8.9 ft) in length and 250 kilograms (551.2 lb) in weight— making it smaller than the bigger dolphinDolphin
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...
s. The species makes slow, deliberate movements with little splash or blow and usually lies motionless when at the sea's surface. Consequently it can be observed only in very calm seas.
The Dwarf Sperm Whale is similar in appearance and behavior to its cousin the Pygmy Sperm Whale
Pygmy Sperm Whale
The Pygmy Sperm Whale is one of three species of toothed whale in the sperm whale family. They are not often sighted at sea, and most of what is known about them comes from the examination of stranded specimens.-Taxonomy:...
. Identification may be close to impossible at sea – however, the Dwarf is slightly smaller and has a larger 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...
. The body is mainly bluish gray with a lighter underside with slightly yellow vein
Vein
In the circulatory system, veins are blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart...
-like streaks possibly visible. There is a white false gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
behind each eye. The flippers are very short and broad. The top of the snout
Snout
The snout, or muzzle, is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw.-Terminology:The term "muzzle", used as a noun, can be ambiguous...
overhangs the lower jaw
Jaw
The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...
, which is small. Dwarfs have long, curved and sharp teeth (0–6 in the upper jaw, between 14 and 26 in the lower). These teeth led to the species being described as the "rat
Rat
Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus...
porpoise
Porpoise
Porpoises are small cetaceans of the family Phocoenidae; they are related to whales and dolphins. They are distinct from dolphins, although the word "porpoise" has been used to refer to any small dolphin, especially by sailors and fishermen...
" in the Lower Antilles
Netherlands Antilles
The Netherlands Antilles , also referred to informally as the Dutch Antilles, was an autonomous Caribbean country within the Kingdom of the Netherlands, consisting of two groups of islands in the Lesser Antilles: Aruba, Bonaire and Curaçao , in Leeward Antilles just off the Venezuelan coast; and Sint...
.
Like other Sperm Whales, the Dwarf Sperm Whale has a spermaceti
Spermaceti
Spermaceti is a wax present in the head cavities of the sperm whale . Originally mistaken for the whales' sperm , spermaceti is created in the spermaceti organ inside the whale's head and connected to its nasal passage...
organ in its forehead. Like the pygmy, the dwarf is able to expel a dark reddish substance when frightened or attacked—possibly to put off any predators.
Dwarf sperm whales are usually solitary but have occasionally been seen in small groups. They feed mainly on 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 crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
.
Population and distribution
The Dwarf Sperm Whale prefers deep water, but is more coastal than the pygmy sperm. Its favorite habitat appears to be just off the continental shelfContinental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...
. In the Atlantic, strandings have been observed in Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
in the west and Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
, United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
in the east, and as far south as southern Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
and the tip of Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
. In the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
, specimens have been found on the south coast of Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and on many places along the Indian Ocean's northern coast - from South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
right round to Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
. In the Pacific, the known range includes the Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
ese coast and British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
. No global population estimates have been made. One survey estimated a population of about 11,000 in the eastern Pacific.