Kogia sima

2. Dwarf Sperm Whale Kogia sima

French: Cachalot nain / German: Kleinstpottwal / Spanish: Cachalote enano

Other common names: Owen's Pygmy Whale, Snub-nosed Cachalot

Taxonomy. Physeter simus Owen, 1866,

India, Andhra Pradesh (= Madras Presidency), “taken at Waltair,” near Vishaknaptnam.

Rules of Latin gender agreement and scientific nomenclature establish that sima is the correct spelling for the species name, rather than the widely used simus. Recent genetic evidence suggests that the Atlantic Ocean population may be distinct from K. sima occupying the Indian and Pacific oceans. Monotypic.

Distribution. Apparently mainly tropical, but also temperate waters of the Atlantic, Pacific, and Indian oceans; stranding records concentrated on Atlantic and Pacific coasts of S USA, South Africa, and S coast of the Arabian Peninsula; a single record exists for the Mediterranean (Italy). Precise atsea distribution is unknown.

Descriptive notes. Total length 200-270 cm; weight 136-280 kg. Condylobasal length of the skull of the Dwarf Sperm Whale is 26.2-30.3 cm, significantly smaller than that of the Pygmy Sperm Whale (K. breviceps) at 39.1-46.9 cm. The Dwarf Sperm Whale is variable in color, but it is generally blackish-brown dorsally, shading to cream on its belly. Relative position of foramen magnum near midpoint of skull height in the Dwarf Sperm Whale is well above midpoint of skull height in the Pygmy Sperm Whale; this characteristic has been reported to be diagnostic, but overlap in this feature has been noted in individuals from South African waters. Other diagnostic cranial characteristics include sagittal septum (narrow, 6-14 mm, with near vertical sides in the Dwarf sperm Whale and broad, 2.3-8 cm, with gradually sloping sides in the Pygmy Sperm Whale) and degree of slope from dorsal rim of cranial fossae (steep in the Dwarf Sperm Whale and gradual in the Pygmy Sperm Whale). Dorsal fin of the Dwarf Sperm Whale is greater than 5% of total body length and is taller than that of the Pygmy Sperm Whale. The Dwarf Sperm Whale has a shorter snout that the Pygmy Sperm Whale, and distance between snout and anterior insertion of dorsal fin is less than 50% of total body length. Lowerjaw of the Dwarf Sperm Whale has 8-13 teeth on each side and up to three in each upper jaw.

Habitat. Continental shelf and slope, frequently in waters with depths of 900-1500 m. Although the Dwarf Sperm Whale is considered pelagic, it is occurs in more coastal areas and shows preferences for higher water temperatures and more tropical seas than the Pygmy Sperm Whale.

Food and Feeding. The Dwarf Sperm Whale feeds on the same main squid species as does the Pygmy Sperm Whale, but it eats larger squid, has a narrower range of prey species, and feeds in shallower water. Apparently, the smaller geographic distribution and shorter mating and birthing periods of the Dwarf Sperm Whale (four months vs. six months in the Pygmy Sperm Whale) results in this more specialized feeding strategy. Cephalopods associated with continental shelf habitats are found frequently in stomachs of Dwarf Sperm Whales stranded on South Africa and Taiwan, perhaps reflecting the more shoreward distribution of the Dwarf Sperm Whale compared with the Pygmy Sperm Whale.

Breeding. Sexual maturity of the Dwarf Sperm Whale in South African is reached at a length of ¢.200 cm and 2-6-3 years old in males and ¢.210 cm and 4-5 years in females. Length and weight at birth are estimated at 95-110 cm and 14 kg, respectively.

Activity patterns. Dive times of 14-30 minutes have been recorded for Dwarf Sperm Whales in the Gulf of California. Elsewhere, average dive duration of eleven minutes has been calculated. Periods at the surface are brief for active Dwarf Sperm Whales, lasting 1-3 minutes.

Movements, Home range and Social organization. Maximum group size of Dwarf Sperm Whales observed at sea is somewhat larger than for Pygmy Sperm Whales; groups are typically 1-12 individuals. Groups are 1-5 individuals in the eastern tropical Pacific and western Indian oceans. Median group size is 3-5 individuals off the Bahamas and 2-3 individuals off Hawaii. Maximum number of individuals recorded stranding simultaneously is four immature individuals (one male and three females). Off the Bahamas, Dwarf Sperm Whales seems to undertake seasonal movements, with small groups of 1-8 individuals occupying the deepest water habitat (900-1600 m) in May-October and somewhat larger groups of 1-12 individuals observed moving into shallower (400-900 m) slope habitat in November—April. It is hypothesized that efforts to avoid sharks may reduce group size and cause movement of Dwarf Sperm Whales into deeper water off the Bahamas in summer. Nothing is known of social organization of the Dwarf Sperm Whale.

Status and Conservation. CITES Appendix II. Classified as Data Deficient on The [UCN Red List. Nevertheless, the true conservation status of the Dwarf Sperm Whale is uncertain and may range from Least Concern to a more threatened category. There are no estimates of global abundance of the Dwarf Sperm Whale. Population estimates from specific regions in 1993-2006 should be considered provisional, but they suggested 19,172 and 11,200 Dwarf Sperm Whales off Hawaii and in the eastern tropical Pacific Ocean, respectively, and 395 Dwarf Sperm Whales and Pygmy Sperm Whales, collectively, in the western North Atlantic Ocean and 742 in the northern Gulf of Mexico. A subsequent estimate suggested 150,000 Dwarf Sperm Whales and Pygmy Sperm Whales, collectively, in the eastern tropical Pacific Ocean based on data collected between 1986 and 1996. Current information is insufficient to evaluate population trends.

Bibliography. Baccetti et al. (1991), Dunphy-Daly et al. (2008), Katona et al. (1983), Marino et al. (2003), Nagorsen (1985), Scott & Cordaro (1987), Taylor et al. (20084), Willis & Baird (1998).