Dwarf Sperm Whale

## Description

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 tail in the other.

The dwarf sperm whale is a suction feeder that mainly eats squid, and does this in small pods of typically one to four 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. 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 by the International Union for Conservation of Nature (IUCN) is least concern.

## Appearance

A small whale (smaller than some dolphins), Dwarf sperm whale is a rare and insufficiently explored species. Most of the available information about this animal is taken from occasional strandings. Dwarf sperm whale is quite similar and closely related to the pygmy sperm whale: when found at sea, these two species usually seem to be the same. According to recently conducted genetic studies, it's possible that there are two separate species of Dwarf sperm whale: one in the Atlantic Ocean, and another in the Indo-Pacific.

## Distribution

The area of their distribution stretches through all of the world's oceans. Dwarf sperm whales are most frequently found in deep tropical and temperate waters over the edge of a continental shelf. They can occasionally be observed close to the shore in the Gulf of California as well as in the warmer waters off the southern tip of South Africa.

## Behavior

These animals have been observed both solitary and in groups, consisting of 6 - 10 individuals. They are slow and cautious swimmers. When coming to the surface, they usually rise slowly and then disappear. Other times, they can often be seen simply floating motionless at the surface. Dwarf sperm whales do not tend to approach vessels, but are known to allow vessels to approach them as they bask on the surface. There is an opinion that they are able to dive at depths of more than 1,000 feet (300 meters) when foraging. They are likely to use echolocation when looking for prey. Due to their cautiousness, lack of a visible blow as well as low profile/appearance in the water, these animals are extremely difficult to come across at sea. They can only be observed in ideal conditions such as calm sea, little or no swells and low wind speed.

## Diet

Dwarf sperm whales are carnivores (molluscivores), they feed upon crustaceans, including shrimp and crabs. They also favor fish and cephalopods such as squid and octopus.

## Reproduction

There is no information on the mating system of dwarf sperm whales and very little is known about their reproductive habits. They are likely to breed in autumn or winter, giving birth in summer of the following year. Gestation period lasts for 9 - 11 months, yielding a single baby. The mother nurses and suckles the calf, which is likely to be weaned by one year old, when it reaches 5 feet (1.5 meter) in length. Sexual maturity is reached at 2.5 - 5 years old, which coincides with a length of 7 feet (2 meters).

## Population

### Population threats

Currently, there’s a huge number of threats to this species' population. Thus, the dwarf sperm whales are exposed to ship strikes due to their habit of floating motionless at the surface. As deep-diving whales, they are highly threatened by underwater sounds and anthropogenic noise, which are very dangerous to these animals. Another big threat is entanglement and incidental by-catch due to interaction with fisheries and, particularly, drift gillnets. Living near seashore, they are threatened by human activities and pollution in a form of marine debris: some stranded specimens have been found with blocked intestinal tracks because of ingesting garbage such as plastic, while others have had serious health problems, including degenerative heart disease, immune system problems and heavy parasite infestations.

### Population number

According to the IUCN Red List, the global population size of the Dwarf sperm whale is unknown for today. However, specific populations have been estimated in some areas: off Hawaii - 19,172 whales; the northern Gulf of Mexico – 742 whales; the western North Atlantic – 395 whales; the eastern tropical Pacific - 150,000 whales. Currently, Dwarf sperm whales are classified as Data Deficient (DD) on the IUCN Red List.

## Fun Facts for Kids

The pygmy and dwarf sperm whales were determined as two separate species in 1966, by a scientist at the Smithsonian Institution (Washington D.C.).

Dwarf sperm whales stand out of other cetaceans due to the use of the "squid tactic": this is when a threatened animal ejects liquid. Like cephalopods such as squids, these whales are able to eject this liquid, giving out as much as 3 gallons (12 liters) of it at a time. They use this ability as a technique of self-defense, creating a dense cloud, which acts like diversion; while the opponent is confused, the whale has time to escape.

The upper jaw of the animal holds up to 6 teeth, while the lower jaw has 16 - 24 teeth.

When swimming, whales move their tails up and down. They also use their flippers, which also aid them when making turns.

Whales usually sleep right below the surface so that their blowhole remains above the surface. They occasionally come to the surface, releasing air from their blowhole, which creates a stream of watery mist known as a "blow".