True's Beaked Whale

So excited by his discovery of True's Beaked Whale, Frederick True gave it the species name 'mirus', meaning 'wonderful'.

Identification

Freshly stranded Southern Hemisphere True's, or 'Wonderful', Beaked Whales are dark grey-black on the upper part, flanks and belly of the body from the head almost to the dorsal fin. They have dark eye-patches. The lower jaw and body from the caudal to the dorsal fin and between the genital and anal regions are white. They may have black speckling on the jaw and throat. The colouration is different in Northern Hemisphere animals. Adults may reach 5.3m in length, with weight up to 1.5 tonnes. At birth these whales are about 2.2m long. The body is rounded in the middle and tapered towards both ends. The head is small with a short, cone-shaped beak. The melon is small, but well-rounded, sloping steeply to a relatively short beak. Males have a single pair of teeth at the tip of the lower jaw. These teeth are angled forward and are visible when the jaws are closed. Nearly all the tooth that erupts from the lower jaw is exposed in the live animal. The slightly hooked dorsal fin is positioned between about 60 and 70% of the distance between the beak and the tail flukes. The flippers are small and paddle-shaped and, when at rest, fit into shallow recesses in the body wall. (These flipper pockets are present in most beaked whales.)

True's Beaked Whales may be almost impossible to positively identify at sea. They may be confused with Hector's Beaked Whales, as the males of both species have a pair of triangular teeth set at the apex of the lower jaw. However, the teeth of male Hector's Beaked Whales are positioned 2-3cm behind the tip of the lower jaw, rather than right at the tip.

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.

Alternative name/s

Wonderful Whale.

Distribution

True's Beaked Whales are found in cool temperate, deep oceanic waters. This species has a uniquely disjunct distribution, occurring in the northern North Atlantic Ocean, as well as the southern regions of the Indian and Pacific Oceans. Strandings in southern Australia (Western Australia, Victoria and Tasmania) and South Africa suggest that there may be localized populations of True's Beaked Whales in these regions. Given the disjunct distribution of this species, there may be grounds for recognizing the Northern and Southern Hemisphere forms as distinct subspecies.

Feeding and diet

Nothing is known about the diet of this species, but 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.

Life history cycle

Little is known about breeding in this species. Three animals likely to be True's Beaked Whales (possibly two adult females and a large calf) were observed off Hatteras Inlet, North Carolina, and an adult female with calf were stranded in South Africa. Sightings are rare due to their deep-ocean distribution, elusive behaviour and possible low numbers.

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 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. True's Beaked Whale. In National Audubon Society Guide to Marine Mammals of the World. Pp. 276-277. Chanticleer Press, Inc., New York.
• Ross, G. J. B. 1969. Evidence for a southern breeding population of True's beaked whale. Nature 222: 585.
• Ross, G. J. B. 1984. The smaller cetaceans of the south east coast of southern Africa. Annals of the Cape Provincial Museum (Natural History) 15: 173-410.