Andrews' Beaked Whale

Introduction

Andrews' Beaked Whale is known from strandings of only about 35 animals. They appear to avoid vessels and are rarely seen at sea.

Identification

Andrews' Beaked Whale was first recorded on New Brighton Beach, New Zealand in 1904. It was described in 1908 by R. C. Andrews and named after George Bowdoin, a trustee of the American Museum of Natural History. The species is known from strandings of only about 35 animals. They appear to avoid vessels and are rarely seen at sea.

Their colour is predominantly dark blue-black. The tip of the beak, as far as the posterior edge of the teeth, is white. The ventral side of the flanks may also be paler. Adult males sometimes have a greyish 'saddle' from behind the blowhole to the dorsal fin. Females have less white on the beak. Adult males are often covered with many long, linear tooth-rake scars (probably inflicted by other males), and both sexes may have oval scars from cookie-cutter shark bites.

It has a deep, round body at mid-length and a narrow head. The melon is not prominent. The beak is short and thick, and the lower jaw has a distinctive upward arch. This arch is more pronounced in males than females.

Adult males have a pair of large teeth set about halfway along the lower jaw at the apex of the arch. These teeth curve outwards slightly to lie outside the upper jaw. They are wide and flat, with a straight anterior, or front, edge, a convexly curved posterior edge and a forward-pointing denticle at the tip. The erupted teeth are mostly covered by skin and gum tissue, so only the tip of each tooth is exposed. As is typical of beaked whales, the teeth do not erupt in females. The dorsal fin is small and triangular with a rounded tip.

Andrews' Beaked Whale may be confused with Blainville's Beaked Whale. The jawline of Blainville's Beaked Whale (also toothed in males) is much more highly arched than that of Andrews' Beaked Whale. Andrews' Beaked Whale has a proportionally longer beak. Ginkgo-toothed Beaked Whales are difficult to distinguish from Andrews' Beaked Whales at sea, but the teeth of these whales barely protrude above the gum, unlike those of Andrews' Beaked Whales.

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

Andrews' Beaked Whales are found in temperate waters of the Southern Hemisphere (usually between 32° and 54°S), north of the Antarctic Convergence. Most records are from strandings in New Zealand, Australia and subantarctic Macquarie and Campbell Islands. As it is seen so rarely, it is possible that this species may live in deep water, far from land.

Feeding and diet

Although the details of the diet of this species are not known, these whales are presumed to feed on deepwater squid and fish, and possibly crustaceans and echinoderms (sea urchins and starfish) found on the sea floor. Because they lack functional teeth, they presumably capture most of their prey by suction.

Breeding behaviours

These whales are mainly known from stranded dead animals. They are rarely seen at sea due to their deep-ocean distribution, elusive behaviour, and possible low numbers, so virtually nothing is known of the breeding and general behaviour of this species. The calving season in New Zealand waters appears to be during summer and autumn.

References

• Baker, A. N. 1999. Whales and Dolphins of Australia and New Zealand: an identification guide. Allen & Unwin, St Leonards.
• Baker, A. N. 2001. Status, relationships and distribution of Mesoplodon bowdoini Andrews, 1908 (Cetacea: Ziphiidae). Marine Mammal Science 17: 473-493.
• 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 14. Beaked whales of the genus Mesoplodon. In Handbook of Marine Mammals. Pp. 349-430. (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. Andrews' Beaked Whale. In National Audubon Society Guide to Marine Mammals of the World. Pp. 286-287. Chanticleer Press, Inc., New York.