Dwarf sperm whale

The dwarf sperm whale (Kogia sima) is a sperm whale that inhabits temperate and tropical oceans worldwide, in particular continental shelves and slopes. It was first described by biologist Richard Owen in 1866, based on illustrations by naturalist Sir Walter Elliot. The species was considered to be synonymous with the pygmy sperm whale (Kogia breviceps) from 1878 until 1998. The dwarf sperm whale is a small whale, 2 to 2.7 m (6 ft 7 in to 8 ft 10 in) and 136 to 272 kg (300 to 600 lb), that has a gray 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 on the body–nearer the middle in the dwarf sperm whale and nearer the back in the other. The dwarf sperm whale is a suction feeder that mainly eats squid, and does this in small pods of typically 1 to 4 members. It is preyed upon by the killer whale (Orcinus orca) and large sharks such as the great white shark (Carcharodon carcharius). When startled, the whale can eject a cloud of red-brown fluid, similar to a squid. 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 more threatened by ingesting or getting entangled by marine debris. No global population estimate has been made, and so its conservation status by the International Union for Conservation of Nature (IUCN) is data deficient. The first two dwarf sperm whale specimens, 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 pygmy sperm whale (now Kogia breviceps), with Euphysetes acting as a subgenus. The species name simus is Latin for 'stump-nosed', a reference to its blunt snout. John Edward Gray, when he created the genus Kogia 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 1871, mammalogist Theodore Gill 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 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 Charles Handley from 1966, and mammalogist 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. The dwarf sperm whale can range in size from 2 to 2.7 m (6.6 to 8.9 ft) in length and 136 to 272 kg (300 to 600 lb) in weight—less than the 4.25 m (14 ft) and 417 kg (920 lb) pygmy sperm whale. A newborn is generally around 1 m (3 ft 3 in) long and 14 kg (31 lb). Males are thought to reach physical maturity at age 15, and females age 13. Sexual maturity, which happens after an individual has attained 2–2.2 m (6 ft 7 in–7 ft 3 in) 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-gray or blue-gray coloration with a lighter-gray 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 dorsal fin 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.