Gray's Beaked Whale

Gray's Beaked Whale is the second-most commonly stranded of the beaked whales in Australia, and is the most common beaked whale to strand in New Zealand.

Identification

This species was described from the remains of animals found at a mass stranding involving approximately 28 whales in the Chatham Islands off New Zealand in 1874. It was described in 1876 by von Haast, and named after the former Director of the British Museum, John E. Gray, who had died the year before. (Gray had described no less than three new species of beaked whale during his career: Hector's, the Strap-toothed and the Spade-toothed Beaked Whale.)

Gray's Beaked Whales are dark bluish-grey dorsally and paler below. The beak and anterior part of the forehead are light grey or white. Adult females may be slightly lighter dorsally than adult males. Animals of both sexes may carry circular white scars from bites inflicted by cookie-cutter sharks (as may all beaked whales and many other cetaceans). Males may also be marked with numerous single, linear, tooth-rake scars, probably inflicted by other males. The beak is long and cylindrical and the mouthline is straight. There is no noticeable bulge on the forehead, but the melon does bulge slightly just in front of the blowhole. In males, there is a single mandibular tooth positioned near the middle of each side of the jaw. In adult males, these teeth tilt forward slightly and are large and triangular; they may grow up to 10 cm wide, although approximately 6 cm wide is more common. There is also a row 17-22 small, vestigial, teeth towards the rear of the upper jaw in adults of both sexes. These teeth are not attached to the bone and, in females, do not emerge from the gums. The dorsal fin is hooked and quite pointed.

The long white beak protrudes from the water as the animal surfaces to breathe. Two or three animals, as well as larger aggregations, have been sighted at sea. Gray's Beaked Whale is the second-most commonly stranded of the beaked whales in Australia, and is the most common beaked whale to strand in New Zealand. Strandings of up to 28 individuals have occurred, suggesting this species may be more gregarious than some of the other beaked whales. Gray's Beaked Whale is known to breach and 'porpoise' when traveling fast at the surface.

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. This approach was used recently to identify a live Gray's Beaked Whale swimming close to shore at Busselton, Western Australia. A sample of sloughed skin for DNA analysis was obtained from this animal using a scrubby pad (kitchen pot scourer) that was passed along its flank as it swam past.

Alternative name/s

Scamperdown Whale

Distribution

Gray's Beaked Whales have a circumpolar Southern Hemisphere distribution, occurring in cold temperate waters mainly between 30° and 45°S, with a northern limit of about 25°S. Sightings and strandings suggest that the species is common in the Indian Ocean, south and east of Madagascar, as well as off South America, the Falkland Islands, New Zealand and Western Australia. It is a relatively commonly stranded beaked whale on southern Australian coasts. There is one record of this species from the Northern Hemisphere: a female stranded in The Netherlands. The animal is thought to have been an anomalous stray.

Feeding and diet

Nothing is known about the diet of this species. It is presumed to feed on deep-sea fish and squid, 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.

Life history cycle

Little is known about breeding and general behaviour in this species. Sightings are rare due to their deep-ocean distribution, elusive behaviour and possible low numbers. Strandings in New Zealand and around southern Australia occur mostly during the summer and autumn from December to April, suggesting there may be seasonal movement inshore to calve.

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.
• Gales, N. J., Dalebout, M. L., and Bannister, J. 2002. Genetic identification and biological observation of two free-swimming beaked whales: Hector's Beaked Whale (Mesoplodon hectori, Gray, 1871), and Gray's Beaked Whale (Mesoplodon grayi, Von Haast, 1876). Marine Mammal Science 18: 544-551.
• 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. Gray's Beaked Whale. In National Audubon Society Guide to Marine Mammals of the World. Pp. 282-283. Chanticleer Press, Inc., New York.