Pygmy Sperm Whale

The Pygmy Sperm Whale (Kogia breviceps) is one of three species of whale in the Sperm Whale family . They are not often sighted at sea and most of our understanding of the creaturescomes from the study of washed-up specimens

Taxonomy

There has been debate and differing opinion as to the correct classification of the Pygmy and Dwarf Sperm Whales (see Sperm Whale family for details). Until 1966, the two species were widely considered to actually be thesame species. That year a scientist at the SmithsonianInstitute definitively diagnosed them as separate species. The Pygmy Sperm Whale was first named by Blainville in 1838.

Physical description

Like its giant cousin, the Sperm Whale , the Pygmy Sperm Whale has aspermaceti organ in its forehead (see the Sperm Whale for a discussion of itspurpose). It also has a sac in its intestines that contains a dark red fluid. The whale will expel this fluid when frightened.Its purpose is believed to be to confuse and disorientate predators.

The Pygmy Sperm is amongst the smallest of all whales and is not much larger than many dolphins . They are about 1.2m at birth, growing to about 3.5m at maturity. Adults weigh about 400kg. Roughlyspeaking the underside is a creamy, occasionally pinkish, colour and the back and sides are a bluish grey. However there isconsiderable intermixing between the two colours. The head is large in comparison to body size, given an almost swollenappearance when viewed from the side. The lower jaw is very small and slung low. The blowhole is displaced slightly to the leftwhen viewed from above facing forward. The dorsal fin is very small indeed andhooked. Its size is considerablely smaller than the Dwarf Sperm Whale and may this may be used for diagnostic purposes. The PygmySperm has between 20 and 32 teeth all of which are set into the lower jaw only. There is false gill behind each eye.

This whale makes very inconspicious movements. It rises to the surface slowly, with little splash or blow, and will remainthere motionless for some time. In Japan the whale was historically known as the "floating whale" because of this. Its dive isequally lacking in grand flourish - it simply drops out of view. The species has a tendency to back away from rather thanapproach boats. Breaching has been observed, but is not common.

Pygmy Sperms are usually solitary creatures but have been seen in groups of upto six. Primary food sources are squid and crabs .

Population and distribution

Pymgy Sperm Whales are found in the temperature waters of the Atlantic, Pacific and Indian Oceans. However they are rarelysighted at sea so most data comes from stranded animals - making a precise range and migration map difficult. They are believedto prefer off-shore waters. Their status is usually described as rare but occasional patches of higher density of strandingssuggest it may be more common rather previously supposed. The total population is unknown.

Human interaction

Pymgy Sperm Whales have never been hunted on a wide scale. Land-based whales have hunted them from Indonesia , Japan and the Lesser Antilles . Individuals have also been recorded killed in drift nets. Some stranded animals have beenfound with plastic bags in their stomachs - which may be a cause for concern. It is not known whether these activities arecausing long-term damage to the survival of the species.

References

1. Pygmy and Dwarf Sperm Whales by Donald F. McAlpine in Encyclopedia of Marine Mammals pp. 1007-1009 ISBN 01255513402
2. Whales Dolphins and Porpoises, Mark Carwardine, Dorling Kindersley Handbooks, ISBN 0751327816
3. National Audubon Society Guide to Marine Mammals of the World, Reeves, Stewart, Clapham and Powell, ISBN 0375411410