Kogia breviceps (de Blainville, 1838)

English: Pygmy sperm whale
German: Zwergpottwal
Spanish: Cachalote pigmeo
French: Cachalot pygmée

1. Description

Kogia spp. are porpoiselike, and robust, with a distinctive underslung jaw, not unlike sharks. They have the shortest rostrum among cetaceans and the skull is markedly asymmetrical. Pygmy sperm whales reach a maximum size of about 3.8 m total length and a body mass of 450 kg. Colouration in adults is dark blueish grey to blackish brown on the back with a light venter. On the side of the head, between the eye and the flipper, there is often a crescent-shaped, light-coloured mark referred to as a "false gill" (McAlpine, 2002).

2. Distribution

The Pygmy sperm whale is evidently an oceanic species that lives mostly beyond the edge of the continental shelf in tropical and temperate waters around the world. It ranges north to Nova Scotia, the Acôres, the Netherlands, Miyagi on the east coast of Honshu, Hawaii, and northern Washington State. It ranges south to Uruguay, Cape Province, the Tasman Sea, Islas Juan Fernández, and Arica, Chile (Rice, 1998). It is unknown whether the populations are isolated (Carwardine, 1995). However, Martin and Heyning (1999) reported the cyamid amphipod species Isocyamus kogiae Sedlak-Weinstein (1992) for the first time from a K. breviceps stranded in southern California, extending the known range of the amphipod from Moreton Island, Queensland, Australia, to the northeastern Pacific. This ectoparasite suggests that pigmy sperm whales from both sides of the Pacific are not isolated from each other.

Kogia breviceps is poorly known, though a lack of records of live animals may be due to inconspicuous behaviour rather than rarity. Most information stems from strandings (especially females with calves), which may give an inaccurate picture of the actual distribution at sea (Carwardine, 1995).

3. Population size

In areas where they frequently strand, members of the genus Kogia are considered to be one of the most common species to come ashore. While many large males strand, many Kogia strandings also consist of a female and small calf or a female that has given birth only recently. However, as with K. sima, there are no real estimates of abundance (Caldwell and Caldwell, 1989).

4. Biology and Behaviour

Habitat: K. breviceps seems to prefer warmer waters: there are records from nearly all temperate, subtropical, and tropical seas. It is rarely seen: it tends to live a long distance from shore and has inconspicuous habits. It is often confused with the Dwarf Sperm Whale, which was not recognised as a separate species until 1966. With so few field records, it is uncertain whether the two can be distinguished reliably except at very close range. It appears to be relatively common off the southeastern coast of the USA and around southern Africa, southeastern Australia, and New Zealand (Carwardine, 1995). A total of 28 strandings were reported for Europe until 1991 (Duguy, 1994). Recent strandings were recorded in Hawaii (Mazzuca et al. 1999), Sable Island, Nova Scotia (Zoe and Hooker, 2000), Spain (Abollo et al. 1998), Veracruz, Mexico (Delgado et al. 1998), Chile (Sanino and Yanez, 1997), France (Duguy, 1991), Micronesia (Eldredge, 1991) and South Australia (Kemper, 1991). There was a sighting off Vietnam (Smith et al. 1997).
According to Caldwell and Caldwell (1989) K. breviceps lives in oceanic waters beyond the edge of the continental shelf while K. simus lives over or near the edge of the shelf. However, this separation of both species was not apparent in the study of Mullin et al. (1994) who, by aerial observation, found both species over water depths of 400-600m in the North-Central Gulf of Mexico. These waters of the upper continental slope were also characterised by high zooplankton biomass (Baumgartner et al. 2001).

Behaviour: Similar to K. sima (Carwardine, 1995). When seen at sea, they generally appear slow and sluggish, with no visible blow (Jefferson et al. 1993). K. breviceps is said to be very easy to approach, lying quietly at the surface practically until touched although it will not approach boats by itself and is rather timid, slow moving and deliberate. Like its congener, K. breviceps spends considerable time lying motionless at the surface with the back of the head exposed and the tail hanging down loosely. K. breviceps is reported to float higher in the water with more of the head and back exposed than K. sima (Caldwell and Caldwell, 1989).

Schooling: Most sightings of pygmy sperm whales are of small groups of less than 5 or 6 individuals. Almost nothing is known of the behaviour and ecology of this species (Jefferson et al. 1993).

Food: Studies of feeding habits, based on stomach contents of stranded animals, suggest that this species feeds in deep water on cephalopods and, less often, on deep-sea fishes and shrimps (Caldwell and Caldwell, 1989; Jefferson et al. 1993; Santos and Haimovici, 1998).

5. Migration

Stranding data of both Kogiidae do not seem to bear out any strong seasonal changes in distribution nor any migrations, although some writers have suggested such in very general terms (Caldwell and Caldwel, 1989). Duguy (1994) suggests that the species may migrate from the coast to the open sea in summer, since most strandings e.g. In Florida occurred during winter and fall. In Europe, there are more strandings in winter, which supports this hypothesis.

6. Threats

Direct catch: Pygmy sperm whales have never been hunted commercially. Small numbers have been taken in coastal whaling operations off Japan and Indonesia (Jefferson et al. 1993).

Incidental catch: A few have been killed in Sri Lanka's gillnet fisheries, and it is likely they are killed in gillnets elsewhere as well (Jefferson et al. 1993). Perez et al. (2001) report on occasional by-catches in fisheries in the north-east Atlantic. However, although it is taken in small numbers both directly and incidentally in fisheries, Baird et al. (1996) find no serious threats to its status.

Pollution: Watanabe et al. (2000) present data on organic pollutants found in small cetaceans stranded on the coast of Florida and Marcovecchio et al. (1994) summarise the available knowledge on environmental contamination in marine mammals off Argentina. Tarpley and Marwitz (1993) report on a young male pygmy sperm whale stranded alive on Galveston Island, Texas, USA which died in a holding tank 11 days later. During necropsy, the first two stomach compartments (forestomach and fundic chamber) were found to be completely occluded by various plastic bags.

7. Remarks

This species is insufficiently known with respect to all aspects of its biology and potential threats. Collection of by-catch and sighting data is strongly needed. For recommendations on Southeast Asian stocks, see Perrin et al. (1996). Not listed by the IUCN or by CMS.

8. Sources

© Boris Culik, Kiel, Germany, 2003

Jede Veröffentlichung dieses Textes im Printbereich oder Internet ist - auch auszugsweise - ohne Genehmigung des Autors ausdrücklich untersagt.