The pygmy sperm whale (Kogia breviceps)

Nov 22, 2014 Features / Columnists, Interesting Creatures in Guyana

The pygmy sperm whale (Kogia breviceps) is one of three species of toothed whale in the

Pygmy sperm whale

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.
There has been debate and differing opinion as to the correct classification of the pygmy and dwarf sperm whales. The two were widely considered to be the same species, until 1966, when a scientist at the Smithsonian Institution definitively identified them as separate species.
The pygmy sperm whale was first named by Henri Marie Ducrotay de Blainville in 1838.
This whale is not much larger than many dolphins. They are about 1.2 metres (3 ft 11 in) at birth, growing to about 3.5 metres (11 ft) at maturity. Adults weigh about 400 kilograms (880 lb). The underside is a creamy, occasionally pinkish, colour and the back and sides are a bluish grey; there is, however, considerable intermixing between the two colours.
The shark-like head is large in comparison to body size, given an almost swollen appearance when viewed from the side. There is a whitish marking, often described as a “false gill”, behind each eye.
The lower jaw is very small and slung low. The blowhole is displaced slightly to the left when viewed from above facing forward. The dorsal fin is very small and hooked; its size is considerably smaller than that of the dwarf sperm whale and may be used for diagnostic purposes.
Like its giant cousin, the sperm whale, the pygmy sperm whale has a spermaceti organ in its forehead. It also has a sac in its intestines that contains a dark red fluid. The whale may expel this fluid when frightened, perhaps to confuse and disorient predators.
Pygmy sperm whales have from 50 to 55 vertebrae and from 12 to 14 ribs on either side, although the latter are not necessarily symmetrical, and the hindmost ribs do not connect with the vertebral column. Each of the flippers has seven carpals and a variable number of phalanges in the digits, reportedly ranging from two in the first digit to as many as 10 in the second digit. There is no true innominate bone, which is replaced by a sheet of dense connective tissue. The hyoid bone is unusually large, and presumably has a role in the whale’s suction feeding.
The pygmy sperm has between 20 and 32 teeth, all of which are set into the rostral part of the lower jaw. Unusually, adults lack enamel due to a mutation in the enamelysin gene, although enamel is present in very young individuals.
Like other toothed whales, the pygmy sperm whale has a “melon”, a body of fat and wax in the head that it uses to focus and modulate the sounds it makes. The inner core of the melon has a higher wax content than the outer cortex. The inner core transmits sound more slowly than the outer layer, allowing it to refract sound into a highly directional beam. Behind the melon, separated by a thin membrane, is the spermaceti organ. Both the melon and the spermaceti organ are encased in a thick fibrous coat, resembling a bursa.
The whale produces sound by moving air through the right nasal cavity, which includes a valvular structure, or “museau de singe”, with a thickened vocal reed, functioning like the vocal cords of humans.
The stomach has three chambers. The first chamber, or fore-stomach, is non-glandular, and opens directly into the second, fundic chamber, which is lined by digestive glands. A narrow tube runs from the second to the third, or pyloric, stomach, which is also glandular, and connects, via a sphincter, to the duodenum. Although fermentation of food material apparently occurs in the small intestine, there is no caecum.
Like all toothed whale, the pygmy sperm whale hunts prey by echolocation. The frequencies it uses are mostly ultrasonic, peaking at around 125 kHz.
Although firm details concerning pygmy sperm whale reproduction are limited, they are believed to mate from April to September in the southern hemisphere. Gestation lasts 11 months and, unusually for cetaceans, the female gives birth to the calf head-first. Newborn calves are about 1.2 metres (3 ft 11 in) in length, and are weaned at around one year of age.
The whale makes very inconspicuous movements. It rises to the surface slowly, with little splash or blow, and will remain there motionless for some time. The species has a tendency to back away from rather than approach boats. Breaching has been observed, but is not common.
Pygmy sperm whales are normally either solitary, or found in pairs, but have been seen in groups of up to six. Dives have been estimated to last an average of 11 minutes, although longer dives of up to 45 minutes have been reported.
Analysis of stomach contents suggests that pygmy sperm whales feed primarily on cephalopods, most commonly including bioluminescent species found in midwater environments. The most common prey are reported to include glass squid, and lycoteuthid and ommastrephid squid, although the whales also consume other squid, and octopuses. They have also been reported to eat some deep-sea shrimps, but, compared with dwarf sperm whales, relatively few fish.
Predators may include great white sharks and killer whales.
Pygmy sperm whales are found throughout the tropical and temperate waters of the Atlantic, Pacific and Indian Oceans.
However, they are rarely sighted at sea, so most data come from stranded animals – making a precise range and migration map difficult.
The pygmy sperm whale is covered by the Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas (ASCOBANS) and the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS). 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).
(Source: Wikipedia – The Free Online Encyclopedia)