The right whale dolphins, the Northern Right Whale Dolphin (Lissodelphis borealis) and the Southern Right Whale Dolphin (Lissodelphis peroni), are two of the easiest cetaceans to identify at sea. Both these oceanic dolphins are coloured black and white and have no dorsal fin. Despite scientists being long acquainted with the species (the Northern species was identified by Peale in 1848 and the Southern even earlier - Lacepede, 1804) surprisingly little is known about them in terms of life history and behaviour.

Physical description

Both species have slender bodies, small, pointed flippers and a small fluke. Conspiciously neither species have a dorsal fin. The Northern Right Whale Dolphin is the only dolphin in the Pacific with this property. Similarly the Southern is the only finless dolphin in the southern hemisphere. The two species, apart from the geographical dislocation can be readily distinguished by the extent of the whiteness on the body. Both have white bellies. However the Southern species has more extensive white - including the flanks, flippers, beak and forehead.

Northern males are about 220cm long at sexual maturity. Females are 200cm. Both sexes become mature at about 10 years. New-born Right Whale Dolphins are about half the length of their parents. The Southern species are typically larger (up to 250cm) and heavier (up to 100kg compared with the Northern's maximum of 80-90kg). The dolphins live for about 40 years.

Distribution

The Northern Right Whale Dolphin is widely distributed in the temperate North Pacific in a band running from Kamchatka and mainland Japan in the west to British Columbia down to Baja California in the east. It is not known with certainty if they follow a migratory pattern. However individuals have been observed close to the Californian shore following their main food source, squid, in winter and spring. Such sightings have not been recorded in summer. Otherwise these dolphins are pelagic. No global population estimates exist. There are an estimated 14,000 individuals close to the North American shoreline.

The Southern Right Whale Dolphin has a circumpolar distribution running from about 40&degS to 55&degS. They are sighted in the Tasman Sea in particular.

Behaviour

Both species are highly gregarious. They move in pods of several hundred individuals and sometimes congregate in groups of 3000 [4]. The groups may also contain Dusky Dolphins and Pilot Whales (in the south) and Pacific White-sided Dolphins (in the north). These dolphins are some of the fastest swimmers (in excess of 40km/h). They can by turns become very boisterous and breach and tail-slap or become very quiet and almost undetectable at sea. At high speed they can leap up to 7 metres across the ocean's surface in a graceful bouncing motion.

The species will generally avoid boats, but bow-riding has been recorded on occasion.

No strandings have been recorded for the Northern species. There has been one recorded instance of 77 Southern Right Whale Dolphins stranding on Chatham Island.

Conservation

Neither species is hunted and the long-term survival of the species is currently assessed to be secure under present conditions. However tens of thousands of the northern species were killed in the 1980s due to them becoming caught in oceanic drift gillnets introduced at that time. Gillnets were banned by the United Nations in 1993. Conservation campaigners work vigorously to try to ensure these bans are retained.

Attempts have been made to keep Northern Right Whale Dolphins in aquaria. In most cases they have died for unknown reasons with in three weeks. Exceptionally, one animal survived 15 months in captivity. There have been no attempts to bring a Southern Right Whale Dolphin into captivity.

References

1. National Audobon Society Guide to Marine Mammals of the World ISBN 0375411410
2. Encyclopedia of Marine Mammals ISBN 0125513402
3. Whales, Dolphins and Porpoises, Mark Carwardine, ISBN 0751327816
4. The northern right whale dolphin Lissodelphis borealis in the eastern North Pacific S. Leatherwood and A. Walker (1979) in "Behaviour of Marine Mammals" Vol 3. pp85-141