Longman's Beaked Whale

Longman's Beaked Whales are the least well known of all cetaceans. Until recently, this species was known from only two specimens, including a skull and lower jaw found at Mackay in northern Queensland in 1822.

Identification

The original skull was donated to the Queensland Museum where the curator, Heber Longman, wrote in 1926 that the skull represented a new species of whale. He named it Mesoplodon pacificus, the Pacific Beaked Whale. After the skull from Mackay was described, there were no further reports of this whale for many years and doubts arose regarding its identity and status as a valid species. A comprehensive paper, published by Joseph Moore in 1968, comparing all then-known beaked whales resolved this question. Moore not only showed that Longman's Beaked Whale was a valid species, but suggested that it was sufficiently distinct to warrant its placement in a new genus, Indopacetus. In the same year, Azzaroli described a second Longman's Beaked Whale skull and lower jaw that were discovered in 1955 in a fertiliser factory in Somalia.

Recently, Dr Merel Dalebout was able to obtain DNA from the holotype (first named specimen) of Indopacetus pacificus: the original beachwashed skull from Mackay, Queensland. This was a great achievement considering both the age of the specimen (over 120 years since its discovery) and the fact that it was much weathered by the sun and sea. Mitochondrial DNA sequences from this specimen were added to the beaked whale database that she and her colleagues had compiled. Subsequent comparisons using this database revealed that two beaked whales from South Africa were also Longman's Beaked Whales. These two whales had previously been incorrectly identified as Southern Bottlenose Whales. With this discovery, we now know for the first time what this species looks like because photographs of the South African animals (both juvenile males) were taken at the time of stranding. Now that its appearance is known, comparisons to large, previously unidentified beaked whales observed at sea in the tropical Indian and Pacific Oceans (often referred to as 'Tropical Bottlenose Whales') have confirmed that these animals are also Longman's Beaked Whales. Their similarity in external appearance to the better-known Southern Bottlenose Whale suggests that other Longman's whales may have been similarly misidentified.

The colour pattern of the Adult Longman's Beaked Whales is variable, but dominated by tan to greyish brown tones. The melon is well formed in both sexes and may be whitish in colour. The beak is moderately long. The dorsal fin is long and hooked and set far back on the body. Juveniles are dark grey dorsally, with white sides and a white melon. Behind the blowhole, the head is dark grey-black and features a white 'ear' patch. A band of dark pigment runs down towards the pectoral fin. This species has only one pair of teeth, set at the tip of the lower jaw. If similar to most other beaked whale species, then these teeth only erupt in adult males. However, until adult Longman's Beaked Whales of both sexes are examined, this is yet to be confirmed. The teeth are forwardly inclined at the tip of the jaw, like those of Cuvier's Beaked Whale and the Southern Bottlenose Whale, but the teeth are more oval than round in cross section. The beak has an unusual lateral swelling about halfway along its length.

Longman's Beaked Whales have been seen at sea in tight groups of 5-20 animals, and sometimes up to 100 animals; pods appear to be close-knit and cohesive. The beak and melon are sometimes exposed when they are traveling fast. The blow is low and bushy. Dives are reported to last 18-25 minutes. They are sometimes seen with Short-finned Pilot Whales and Bottlenose Dolphins.

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

Longman's Beaked Whale is restricted to offshore waters of the tropical Pacific and Indian Oceans. There have been no confirmed sightings of this species in the Atlantic Ocean.

Feeding and diet

Nothing is known about the diet of Longman's Beaked Whales, although, based on the examination of the stomach contents of other species, they probably feed on deep-sea fish, 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

Nothing is known about breeding in this species. 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. 2002. Bare bones and beaked whales. Nature Australia Spring 2002 27(6): 65-71.
• 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.
• Pitman, R. L., Palacios, D. M., Brennan, P. L., Balcomb, K. C. I. and Miyashita, T. 1999. Sightings and possible identity of a bottlenose whale in the tropical Indo-Pacific: Indopacetus pacificus? Marine Mammal Science 15: 531-549.
• Reeves, R. R., Stewart, B. S., Clapham, P. J. and Powell, J. A. 2002. Longman's Beaked Whale. In National Audubon Society Guide to Marine Mammals of the World. Pp. 266-267. Chanticleer Press, Inc., New York.