Pygmy sperm whale

Habitat: Deep waters. Feeds in deep zone of continental shelf and slope waters.

Description: Body is dark blue-grey on back, outer margins of flippers, and flukes. Flanks are light grey, belly is dull white, sometimes pinkish. Skin may appear wrinkled. Conical head which becomes squarer with age; no beak. Head is around 1/6 of body length (cf. 1/3 in sperm whale). Oil-filled spermaceti organ is small, lies above skull behind large melon. Throat grooves short, ill-defined. Flippers relatively long, up to 14% of body length, are wide at base, tapering to rounded point. Dorsal fin is low, slightly re-curved, just behind centre of back. Tail has distinct median notch, concave trailing edge. Crescent-shaped, light ‘false gill’ marking on side of head between eye and flippers.

Size: 3.3 m (both sexes similar).

Weight: 300 – 400 kg; 450 kg male reported in east Canada.

Lifespan: Unknown.

Distribution: Poorly known. Probably worldwide in tropical, subtropical, and temperate seas. 12 strandings reported on Atlantic coasts of British Isles between 1966 – 2002. 3 sightings reported from waters around British Isles; 1 in North Sea off north-east England, August 1979; 2 in deep water off north-west Ireland on successive days in June 1982.

Diet and feeding: Predominantly mesopelagic squid, also fish and crustaceans. Females with calves take more inshore species than adult males.

Breeding: Season unknown in north Atlantic. Off southern Africa, breeding occurs April – September, with births taking place March – August. Gestation period estimated at 11 months, lactation lasts 12 months, females ovulate approximately once every 1.5 years; post-partum oestrus occurs, with 24% of all mature animals examined along coast of south Africa found to be simultaneously pregnant and lactating.

Conservation status and population: Listed by IUCN as lower risk / least concern. No estimates for population size or status. Sometimes caught in fishing gear, reported on Caribbean coast of Colombia, Brazil, Japan. Occasionally taken in harpoon fisheries in east Caribbean, Indonesia, Japan. Found in fish markets in Sri Lanka (estimated >80 a year die in fishing gear). Stranded animals frequently show evidence of collision with vessels. Very little information on pollutant levels; examined individuals have shown high zinc levels but generally low levels of other metals, DDT, PCBs. Plastic bags found in the stomach of some individuals may have caused death by starvation

Identification

Robust, dark body. Surfaces slowly with indistinct blow, may lie still at surface. Easily confused with dwarf sperm whale. Noticeably smaller than other beaked whales; slower moving and squarer-headed than blunt-headed dolphins of similar size. Blowhole slightly left of midline. Lower jaw is narrow, ends well behind the tip of the snout, carries 10 – 16 pairs of sharp pointed teeth (none on upper jaw - dwarf sperm whale sometimes has a few teeth here).

Vocalisations: Echolocation clicks recorded at 60 – 200 kHz with dominant frequency at 60 – 200 kHz.