The dwarf sperm whale (''Kogia sima'') is a sperm whale that inhabits temperate and tropical oceans worldwide, in particular continental shelves and

slopes In mathematics, the slope or gradient of a line is a number that describes both the ''direction'' and the ''steepness'' of the line. Slope is often denoted by the letter ''m''; there is no clear answer to the question why the letter ''m'' is used ...

. It was first described by

biologist A biologist is a scientist who conducts research in biology. Biologists are interested in studying life on Earth, whether it is an individual Cell (biology), cell, a multicellular organism, or a Community (ecology), community of Biological inter ...

Richard Owen in 1866, based on illustrations by naturalist Sir Walter Elliot. The species was considered to be synonymous with the

pygmy sperm whale The pygmy sperm whale (''Kogia breviceps'') is one of two extant species in the family Kogiidae in the sperm whale superfamily. They are not often sighted at sea, and most of what is known about them comes from the examination of stranded speci ...

(''Kogia breviceps'') from 1878 until 1998. The dwarf sperm whale is a small whale, and , that has a grey coloration, square head, small jaw, and robust body. Its appearance is very similar to the pygmy sperm whale, distinguished mainly by the position of the

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...

on the body–nearer the middle in the dwarf sperm whale and nearer the tail in the other. The dwarf sperm whale is a

suction feeder Aquatic feeding mechanisms face a special difficulty as compared to feeding on land, because the density of water is about the same as that of the prey, so the prey tends to be pushed away when the mouth is closed. This problem was first identifi ...

that mainly eats squid, and does this in small pods of typically one to four members. It is preyed upon by the

killer whale The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only extant species in the genus ''Orcinus'' and is recognizable by its black-and-white ...

(''Orcinus orca'') and large sharks such as the

great white shark The great white shark (''Carcharodon carcharias''), also known as the white shark, white pointer, or simply great white, is a species of large Lamniformes, mackerel shark which can be found in the coastal surface waters of all the major ocean ...

(''Carcharodon carcharius''). When startled, the whale can eject a cloud of red-brown fluid. Most of what is known of the whale comes from beached individuals, as sightings in the ocean are rare. Many of these stranded whales died from parasitic infestations or heart failure. The dwarf sperm whale is hunted in small numbers around Asia. It is most threatened by ingesting, or getting entangled by, marine debris. No global population estimate has been made, and so its

conservation status The conservation status of a group of organisms (for instance, a species) indicates whether the group still exists and how likely the group is to become extinct in the near future. Many factors are taken into account when assessing conservatio ...

by the

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of nat ...

(IUCN) is least concern.

Taxonomy

The first two dwarf sperm whale

specimen Specimen may refer to: Science and technology * Sample (material), a limited quantity of something which is intended to be similar to and represent a larger amount * Biological specimen or biospecimen, an organic specimen held by a biorepository ...

s, a male and a female, were collected in 1853 by naturalist Sir Walter Elliot, who thought it a kind of porpoise due to the short snout. However, when he sent drawings of these whales – including skeletal diagrams – to biologist Richard Owen to describe, Owen, in his 1866 paper, recognized it as a type of sperm whale in the family Physeteridae based on several similar characteristics, such as having functional teeth in only the lower jaw, a lopsided blowhole leaning towards the left side, and a spermaceti organ. He named it ''Physeter (Euphysetes) simus'', the same genus as the sperm whale (''Physeter macrocephalus'') and the

(now ''Kogia breviceps''), with ''Euphysetes'' acting as a subgenus. The

species name In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...

''simus'' is

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

for "stump-nosed", a reference to its blunt snout.

John Edward Gray John Edward Gray, FRS (12 February 1800 – 7 March 1875) was a British zoologist. He was the elder brother of zoologist George Robert Gray and son of the pharmacologist and botanist Samuel Frederick Gray (1766–1828). The same is used for ...

, when he created the genus ''

Kogia ''Kogia'' is a genus of toothed whales within the superfamily Physeteroidea comprising two extant and two extinct species from the Neogene *Pygmy sperm whale, ''Kogia breviceps'' *Dwarf sperm whale, ''Kogia sima'' *†'' Kogia pusilla'', Italy, ...

'' in 1846, gave no indication to the meaning, but, since the word has a feminine ending, the masculine species name ''simus'' had to be changed to ''sima'' to fit this when the combination ''Kogia simus'' was proposed by various 20th century authors. In 1900, zoologist

Frank Evers Beddard Frank Evers Beddard FRS FRSE (19 June 1858 – 14 July 1925) was an English zoologist. He became a leading authority on annelids, including earthworms. He won the Linnean Medal in 1916 for his book on oligochaetes. Life Beddard was born in ...

speculated that the word "might be a tribute to a Turk of the past surnamed Cogia Effendi, who observed whales in the Mediterranean". In 1871,

mammalogist In zoology, mammalogy is the study of mammals – a class of vertebrates with characteristics such as homeothermic metabolism, fur, four-chambered hearts, and complex nervous system In biology, the nervous system is the highly complex part ...

Theodore Gill Theodore Nicholas Gill (March 21, 1837 – September 25, 1914) was an American ichthyologist, mammalogist, malacologist and librarian. Career Born and educated in New York City under private tutors, Gill early showed interest in natural histo ...

split Physeteridae into two subfamilies: Physterinae with ''Physeter'', and Kogiinae with ''Kogia'' and the now-defunct ''Euphysetes''; this has now been elevated to family, Kogiidae. Gill also proposed the dwarf sperm whale be moved to its own genus, ''Calignathus''. In 1878, naturalist

James Hector Sir James Hector (16 March 1834 – 6 November 1907) was a Scottish-New Zealand geologist, naturalist, and surgeon who accompanied the Palliser Expedition as a surgeon and geologist. He went on to have a lengthy career as a government employe ...

synonymized the dwarf sperm whale with the pygmy sperm whales as ''K. breviceps''. No distinction was made by most authors until mammalogist Dale Rice in his 1998 review of marine mammal taxonomy citing the works of Dr. Teizo Ogawa from 1936, researcher Munesato Yamada from 1954,

zoologist Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the animal kingdom, including the structure, embryology, evolution, classification, habits, and d ...

Charles Handley Charles Overton Handley, Jr. (July 14, 1924 - June 9, 2000) was a zoologist and explorer who conducted various expeditions for the United States government. Born in Longview, Texas, Handley's father was a professor of wildlife management and an av ...

from 1966, and

Graham James Berry Ross from 1979. Genetic testing in 2006 suggests that ''K. sima'' may actually represent two species, one in the Atlantic and one in the Indo-Pacific region. The Cape of Good Hope around South Africa may mark the barrier between these two populations.

Description

The dwarf sperm whale can range in size from in length and in weight—less than the and pygmy sperm whale. A newborn is generally around long and . Males are thought to reach physical maturity at age 15, and females at age 13. Sexual maturity, which happens after an individual has attained in length, happens at 2 to 3 years for males and around 5 for females. Gestation takes place probably over around 9.5 months. The dwarf sperm whale has a dark-grey or blue-grey coloration with a lighter-grey underside, and a pale, crescent-shaped mark between the eye and the flipper, sometimes called a "fake gill", which is characteristic of the genus. Some individuals have been known to have a second crescent-shaped mark, creating a sort of pale ring encircling a darker spot. It has a high

halfway down the length of the body, and two or more throat grooves. The dorsal fin is taller and closer to the head than it is in the pygmy sperm whale, and the back is flatter. Kogia sima

''Kogia'' is identified as having a square head, a small jaw with the snout jutting outward, and a porpoise-like build with a robust body that rapidly decreases towards the tail. They have the shortest snouts of any modern day whale. Characteristic of sperm whales, the left nostril is markedly larger than the right, and it has a spermaceti organ on its skull. The brain weighs around . The eyes are adapted for low-light environments. The dwarf sperm whale has 14 to 24 teeth, rarely 26, in the lower jaw that are sharp, slightly curved backwards, and–like other sperm whales–lack enamel. The teeth rarely exceed in length, smaller than those of the pygmy sperm whale. At most, 6 teeth are in the upper jaws, though in modern sperm whales, upper teeth are defunct. Unique to ''Kogia'', there is a sac which hangs off from the small intestines near the anus that is filled with a dense, red-brown fluid that looks similar to chocolate syrup. When stressed, this fluid is released. The dwarf sperm whale has between 50 and 57

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

e, 7

neck vertebra In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In ...

e, 12 to 14

thoracic vertebra In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebrae and they are intermediate in size between the cervical ...

e, and 29 or 35-to-37

lumbar vertebra The lumbar vertebrae are, in human anatomy, the five vertebrae between the rib cage and the pelvis. They are the largest segments of the vertebral column and are characterized by the absence of the foramen transversarium within the transverse ...

e. The variation can either be due to loss of bones during preparation of a specimen, or individual variations. It is not known to be

sexually dimorphic Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...

Population and distribution

The dwarf sperm whale ranges throughout tropical and temperate oceans of the world and inhabits the continental shelf and

slope In mathematics, the slope or gradient of a line is a number that describes both the ''direction'' and the ''steepness'' of the line. Slope is often denoted by the letter ''m''; there is no clear answer to the question why the letter ''m'' is use ...

area. It seems to prefer warmer waters than the pygmy sperm whale. The dwarf sperm whale is one of the most commonly beached deep-diving whales in the world, though rarely seen at sea, and likewise, most information about the whale comes from examining beached individuals. Diving depth may vary from place to place: a study in the Bahamas placed average depth at around , whereas a study in the deeper waters of Hawaii placed it at around . In the West Pacific, its recorded range spans from Japan to Tasmania and New Zealand, and in the East Pacific from

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

to central Chile. In the Indian Ocean, the whale is reported from Oman, Sri Lanka, India, Thailand, Philippines, Indonesia around

Timor Timor is an island at the southern end of Maritime Southeast Asia, in the north of the Timor Sea. The island is divided between the sovereign states of East Timor on the eastern part and Indonesia on the western part. The Indonesian part, also ...

, western Australia and South Africa. In the West Atlantic, it has been recorded from

Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth ar ...

to southern Brazil, and in the East Atlantic from Italy in the

Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ...

to South Africa. No global population estimation has been made. Population counts have been taken over certain areas, though given the difficulty to distinguish the dwarf sperm whale from the pygmy sperm whale, the overall estimate represents the total number of both species. In the North Atlantic, they are estimated at around 3,785 individuals; in the East Pacific, around 11,200 individuals.

Ecology

Histioteuthis reversa (Michael Vecchione, NOAA)

Diet

The dwarf sperm whale is an

open ocean The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...

predator. The stomach contents of stranded dwarf sperm whales comprise mainly squid and, to a lesser degree, deep sea fish (from the

mesopelagic The mesopelagic zone (Greek μέσον, middle), also known as the middle pelagic or twilight zone, is the part of the pelagic zone that lies between the photic epipelagic and the aphotic bathypelagic zones. It is defined by light, and begins at ...

and bathypelagic zones) and

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...

s. However, crustaceans make up a sizable part of the diets of Hawaiian dwarf sperm whales, up to 15%. The stomach contents of whales washed up in different regions of the world indicate a preference for cock-eyed squid and

glass squid The family Cranchiidae comprises the approximately 60 species of glass squid, also known as cockatoo squid, cranchiid, cranch squid, or bathyscaphoid squid. Cranchiid squid occur in surface and midwater depths of open oceans around the world. The ...

across its range, particularly the elongate jewel squid (''Histioteuthis reversa'') and ''

Taonius ''Taonius'' is a small genus of glass squid. Although it comprises only three recognised species, it has been suggested there may be as many as five species In biology, a species is the basic unit of classification and a taxonomic rank o ...

''. The throat grooves and the developed musculature in the throat in ''Kogia'' are probably adaptations for increasing the volume of the mouth for

suction feeding Aquatic feeding mechanisms face a special difficulty as compared to feeding on land, because the density of water is about the same as that of the prey, so the prey tends to be pushed away when the mouth is closed. This problem was first identifi ...

, possibly the best-developed among

toothed whale The toothed whales (also called odontocetes, systematic name Odontoceti) are a parvorder of cetaceans that includes dolphins, porpoises, and all other whales possessing teeth, such as the beaked whales and sperm whales. Seventy-three species of ...

s. Also, the blunt snout, lack of teeth, and reduced jaw are characteristics seen in other suction feeding toothed whales. The whale uses its sharp teeth to hold onto prey while expelling water from the mouth. Dwarf sperm whale calves typically start eating solid food once they have reached a size of around though are not fully weaned until they reach around . Toothed whale calves generally start eating solid food at around 6 months, and mothers stop lactating after around 18 to 20 months.

Threats

Killer whale The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only extant species in the genus ''Orcinus'' and is recognizable by its black-and-white ...

s (''Orcinus orca'') and sharks are known to prey on the dwarf sperm whale. Dwarf sperm whale remains have been found in the stomachs of

s (''Carcharodon carcharias''), and infestations of the cestode '' Phyllobothrium delphini'' in beached individuals indicates shark attacks since the cestode matures in sharks. The dwarf sperm whale also competes with other squid-eating whales, such as

beaked whale Beaked whales (systematic name Ziphiidae) are a family of cetaceans noted as being one of the least known groups of mammals because of their deep-sea habitat and apparent low abundance. Only three or four of the 24 species are reasonably well-k ...

s. It occupies the same

ecological niche In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of resources and competitors (for ...

in the same regions as the pygmy sperm whale, though the latter can forage in deeper waters and has been known to feed on a wider array of species of larger size. Some beached individuals have had large parasitic infestations which probably lead to their death, particular with nematodes in the stomach and

tapeworm Eucestoda, commonly referred to as tapeworms, is the larger of the two subclasses of flatworms in the class Cestoda (the other subclass is Cestodaria). Larvae have six posterior hooks on the scolex (head), in contrast to the ten-hooked Cesto ...

s in the blubber. In the southeastern United States, stranded dwarf sperm whales were found to have died from heart failure, and heart failure may have led to the stranding itself.

Behavior

''Kogia'' is thought to be slow-moving, rarely displaying rapid surfacing behavior, tending to float at the surface with only the nape and dorsal fin exposed. From the surface, they sink vertically, instead of lifting their tails out of the water to dive, which would create a splash. The dwarf sperm whale congregates into small pods of one to four individuals, though on occasion up to ten, likely due to limited food resources. Small group size and deep foraging grounds in the summer could also be anti-predator behaviors. However, this is less likely as dolphins congregate in large pods with hundreds of members to prevent predation. The whale probably follows seasonal squid migrations from offshore in the summer to nearshore in the winter. It is possible it prefers a slope habitat as it allows the whale to herd squid against the wall, or it causes

upwelling Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nut ...

which the whale can ride on in order to save energy while hunting. Younger animals may congregate in shallower areas and adults in deeper areas; the slope around South Africa may be a nursery grounds. ''Kogia'', unlike other whales, can eject a red-brown fluid when startled, likely to distract predators, similar to squid. This cloud can cover in the water. This species does not whistle, and instead produces

narrowband Narrowband signals are signals that occupy a narrow range of frequencies or that have a small fractional bandwidth. In the audio spectrum, narrowband sounds are sounds that occupy a narrow range of frequencies. In telephony, narrowband is usua ...

high-

frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...

clicks. These clicks are more similar to those produced by some dolphin and porpoise species–such as the

hourglass dolphin The hourglass dolphin (''Lagenorhynchus cruciger'') is a small dolphin in the family Delphinidae that inhabits offshore Antarctic and sub-Antarctic waters. It is commonly seen from ships crossing the Drake Passage, but has a circumpolar dis ...

(''Sagmatias cruciger''),

Hector's dolphin Hector's dolphin (''Cephalorhynchus hectori'') is one of four dolphin species belonging to the genus '' Cephalorhynchus''. Hector's dolphin is the only cetacean endemic to New Zealand, and comprises two subspecies: ''C. h. hectori'', the more n ...

(''Cephalorhynchus hectori''), the

Chilean dolphin The Chilean dolphin (''Cephalorhynchus eutropia''), also known as the black dolphin, is one of four dolphins in the genus ''Cephalorhynchus''. The dolphin is found only off the coast of Chile; it is commonly referred to in the country as ''ton ...

(''Cephalorhynchus eutropia''),

Commerson's dolphin Commerson's dolphin (''Cephalorhynchus commersonii''), also referred to by the common names jacobita, skunk dolphin, piebald dolphin, panda dolphin, or tonina overa (in South America), is a small oceanic dolphin of the genus ''Cephalorhynchus'' ...

(''Cephalorhynchus commersonii''), the

harbour porpoise The harbour porpoise (''Phocoena phocoena'') is one of eight extant species of porpoise. It is one of the smallest species of cetacean. As its name implies, it stays close to coastal areas or river estuaries, and as such, is the most familiar ...

(''Phocoena phocoena''), and

Dall's porpoise Dall's porpoise (''Phocoenoides dalli'') is a species of porpoise endemic to the North Pacific. It is the largest of porpoises and the only member of the genus ''Phocoenoides''. The species is named after American naturalist W. H. Dall. Taxono ...

(''Phocoenoides dalli'')–than to those of other deep-diving whales, such as beaked whales and the sperm whale. The peak frequencies of ''Kogia'' are generally less than 130

kHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that on ...

Relationship with humans

There is some hunting of the dwarf sperm whale in Indonesia, Japan, Sri Lanka, and the

Lesser Antilles The Lesser Antilles ( es, link=no, Antillas Menores; french: link=no, Petites Antilles; pap, Antias Menor; nl, Kleine Antillen) are a group of islands in the Caribbean Sea. Most of them are part of a long, partially volcanic island arc bet ...

as food or bait, though there are no major operations. A bigger threat is likely ingestion of marine debris and entanglement in fishing gear, though it has not been determined how serious a threat these pose. The

(IUCN) currently lists the dwarf sperm whale's

as data deficient, though it could possibly be of

least concern A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. T ...

. The dwarf sperm whale is covered by the

Convention on International Trade in Endangered Species of Wild Fauna and Flora CITES (shorter name for the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention) is a multilateral treaty to protect endangered plants and animals from the threats of intern ...

(CITES), the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area. The species is further included in the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia ( Western African Aquatic Mammals MoU), and the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MoU).

References

External links

Whale & Dolphin Conservation Society (WDCS)
{{Taxonbar, from=Q42669 Sperm whales Fauna of Southeast Asia Cetaceans of the Indian Ocean Cetaceans of the Pacific Ocean Cetaceans of the Atlantic Ocean Mammals described in 1866 Taxa named by Richard Owen