Southern Bottlenose Whale

The Southern Bottlenose Whale was described by William Flower in 1882 from a beach-worn skull found on Lewis Isle in the Dampier Archipelago of north-western Australia. This remains the most northerly record for this species.

Identification

Most descriptions of the colour pattern are largely based on the better-known sister-species of the Southern Bottlenose Whale, the Northern Bottlenose Whale. Adult Southern Bottlenose Whales are brownish-grey, and are darker dorsally than ventrally. Old animals may be light brown or dull yellow. (The brownish colouration in this species may be due to a diatom coating.) The head may be pale, with the pale colour on the melon extending beyond the blowhole. A 6.6m long male that stranded at Ohope, New Zealand in 1979 had a distinct shield-shaped light patch beneath the eyes. Young animals may be black to chocolate brown dorsally and greyish-white ventrally. The body is thick and robust. The melon is very bulbous and may overhang the short, narrow beak. There may be an indentation between the beak and the melon. The head is much larger in adult males than females and rises steeply from the beak. The front surface of the melon may be flattened in old mature males. Adult males also have a single pair of small, conical teeth at the tip of the lower jaw. They slope forwards and slightly outwards and are visible outside the closed mouth. Each tooth has a central peaked denticle. These teeth do not erupt in females. The triangular to slightly sickle-shaped dorsal fin is positioned about two-thirds of the distance from the beak to the tail and is of moderate size (up to about 40cm in length).

The blow is low and bushy and projects forwards slightly. They may be difficult to distinguish at sea from Arnoux's Beaked Whales, although the beak in the latter species is much longer and the melon less pronounced than that of the Southern Bottlenose Whale.

Accurate species identification is difficult for this and most other species of beaked whale, even for stranded animals. Identification of females and juveniles can be particularly problematic. While cranial anatomy and tooth morphology are useful, the distinguishing features may apply only to adults. Recently, molecular genetic techniques have been applied to the identification of beaked whales. A database of mitochondrial DNA sequences has been compiled for all known species, making it possible to reliably assign individual animals to a particular species.

Distribution

Southern Bottlenose Whales are found in the cold temperate waters of the Southern Hemisphere, from the Antarctic throughout the Southern Ocean to about 30°S. It seems they are most common between 58° and 62°S in the Atlantic and eastern Indian Ocean. They are usually found in deep ocean waters and rarely occur inshore. A small number of strandings have been recorded from southern Australia and New Zealand. There have also been some sightings off New South Wales. Other records from north-western Australia and Brazil suggest that Southern Bottlenose Whales may also occur in warmer temperate waters.

Feeding and diet

Compared to the Northern Bottlenose Whale, little is known about the diet of Southern Bottlenose Whales. However, the stomach of an adult female found stranded on Heard Island included beaks from 15 species of squid, as well as fish eye lenses. The stomach of the specimen from Ohope, New Zealand contained 200 squid beaks. The stomachs of an adult male and an adult female from South Africa also contained squid beaks. The squid included species from South African, Antarctic, and subantarctic waters. Because they lack functional teeth, they presumably capture most of their prey by suction.

The Northern Bottlenose Whale is known to dive to great depths to capture food. It is thought that the huge fatty forehead acts as an acoustic lens for beaming of echolocation signals and prey-stunning sound bursts.

Other behaviours and adaptations

These whales have been observed in groups of 3-10 animals and some breaching has also been seen. The beak and melon appear first when surfacing. The flukes may sometimes be raised when they dive deep and they may remain submerged for up to one hour.

Life history cycle

Little is known about the breeding habits of this species. More information is available for the Northern Bottlenose Whale, which was exploited extensively in the north Atlantic Ocean up to the early 1970s. The northern species has a minimum length at sexual maturity of 6.0m for females and 7.5m for males. The gestation period is estimated as 12 months, with a lactation period of at least one year, and a calving interval of two years.

Based on stranding patterns, it is assumed that calving off South Africa takes place in spring or early summer. Evidence from two New Zealand strandings also suggests that the Southern Bottlenose Whale calves in spring.

Conservation status

There has never been a commercial hunt for Southern Bottlenose Whales, but a few were taken by whalers for research purposes. Several animals have been caught accidentally by driftnets in the Tasman Sea between Australia and New Zealand. There are no abundance estimates for this, or any other, species of beaked whale.

References

• Baker, A. N. 1999. Whales and Dolphins of Australia and New Zealand: an identification guide. Allen & Unwin, St Leonards.
• Bryden, M., Marsh, H. & Shaughnessy, P. 1998. Dugongs, Whales, Dolphins and Seals. A guide to the sea mammals of Australasia. Allen & Unwin, St Leonards.
• Carwardine, M. 2000. Whales, Dolphins and Porpoises. Dorling Kindersley, London.
• Dalebout, M. L., van Helden, A. van Waerebeek, K, and Baker, C. S. 1998. Molecular genetic identification of Southern Hemisphere beaked whales. Molecular Ecology 7: 687-694.
• Mead, J. G. 1989. Chapter 13. Bottlenose whales Hyperoodon ampullatus (Forster, 1770) and Hyperoodon planifrons Flower, 1882. In Handbook of Marine Mammals. Pp. 321-348. (Eds S. H. Ridgeway and S. R. Harrison.) Academic Press, London.
• Menkhorst, P. 2001. A Field Guide to Mammals of Australia. Oxford University Press, Melbourne, Australia.
• Reeves, R. R., Stewart, B. S., Clapham, P. J. and Powell, J. A. 2002. Southern Bottlenose Whale. In National Audubon Society Guide to Marine Mammals of the World. Pp. 272-273. Chanticleer Press, Inc., New York.
• Sekiguchi, K., Klages, N., Findlay, K. and Best, P. B. 1993. Feeding habits and possible movements of southern bottlenose whales (Hyperoodon planifrons). Proceedings of the NIPR Symposium on Polar Biology 6: 84-97.
• Slip, D. J., Moore, G. J. and Green, K. 1995. Stomach contents of a southern bottlenose whale, Hyperoodon planifrons, stranded at Heard Island. Marine Mammal Science 11: 575-584.