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beaked whales
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General Description
One of the most poorly known of the marine mammal groups is the family Ziphiidae, the beaked whales. Although the taxonomy of the beaked whales is largely uncertain, there are at present twenty recognised species in six genera. At least five genera and twelve species are seen in New Zealand waters. Of the fourteen recognised species of the genus Mesoplodon, eight species occur within the New Zealand region. Other beaked whales seen off New Zealand are in separate genera, Berardius, Hyperoodon, Tasmacetus, and Ziphius; the latter two genera have one species.
Mesoplodon whales have small heads, long trunks, and short tails, and range between 3.9 m (pygmy beaked whale) and 6.2 m (strap-toothed whale) in length. Whales in the other genera are larger and may grow to almost 10 m (Arnoux's beaked whale). Beaked whales are characterised by a pronounced rostrum or beak, a pair of grooves on the throat, a shallow (if present) notch between the tail flukes, and a dorsal fin set well back on the body. Species vary in the size, shape, and position of their teeth. Most species have only a single pair of teeth, which are pronounced in males, whereas females and juveniles are effectively toothless. In some species the protruding teeth are like tusks that may be used aggressively by males. Strap-toothed whales are so named because, in adult males, two lower teeth grow over the upper jaw and severely limit the mouth opening. The Shepherd's beaked whale is the only species with a full set of teeth in both jaws.
Stranded individuals and limited sightings at sea suggest that most beaked whale species have a Southern Ocean distribution and occur in small groups in cool, temperate waters. Beaked whales are believed to be deep divers. They are thought to be suction feeders and eat mesopelagic squid and fish.
Knowledge of the presence of beaked whales in New Zealand waters is determined from strandings, rather than sightings at sea. Most strandings have occurred south of the Bay of Plenty, particularly on the east coasts, Chatham Islands, and some subantarctic islands. The southern bottlenose whale and the Gray's beaked whale seem to strand more often in New Zealand than elsewhere, and the latter species is prone to mass strandings. A stranded specimen is the only evidence of the New Zealand presence of the pygmy beaked whale, which is usually found in waters east of Peru and Chile and north to California. Cuvier's and Andrews' beaked whales and strap-toothed whales are thought to calve in New Zealand waters during spring or early summer.
Status
The biology, ecology, and population status of beaked whales are poorly known worldwide and this is reflected in their conservation status. Where species have been assessed, beaked whales found in New Zealand waters are ranked by the Department of Conservation as "data deficient". Most species are listed by IUCN as "insufficiently known". Most were never hunted commercially; however some species have been killed in drift nets in the Southern Ocean and are taken in the coastal fisheries of Japan and Indonesia. Southern bottlenose whales are thought to be the most abundant beaked whale in the Antarctic, with about 500,000 animals south of the Antarctic Convergence in summer. The Gray's and the strap-toothed beaked whales are thought to be widespread and fairly common in the Southern Ocean. Andrews' and Hector's beaked whales are considered uncommon.
Key Locations
Most beaked whales are limited to temperate areas of the southern hemisphere, with some species extending further south to the Antarctic continent. This general pattern is exemplified by the Arnoux's beaked whale, the southern bottlenose whale, the Shepherd's beaked whale, the Gray's beaked whale, the Hector's beaked whale, and the strap-toothed whale. Several species appear to be largely restricted to southern Australian and New Zealand waters, including the Andrews' beaked whale and the Hector's beaked whale. A small centre of distribution for the ginkgo-toothed beaked whale near the Antipodes and Bounty islands may be the southern limit for the species, which mainly occurs in tropical and subtropical seas.
Summary of Threats
Due to their open ocean existence, entanglement in drift nets could pose a threat to beaked whales. Due to a paucity of information on the population status of most of the species, it is difficult to determine whether coastal fisheries or other human-induced effects, including seismic surveys, could pose a threat to the overall survival of the species. Natural threats may include parasitic infestation, and predation by sharks, killer whales, and false killer whales.
Typical Habitats
As there are few at-sea observations of beaked whales, it is difficult to identify specific habitat types for individual species. The preferred habitat is deep ocean waters or continental slopes down to about 2000 m.
State of Information
The taxonomy of this family is still uncertain despite recent developments in molecular analysis. The shy nature and far offshore habitat mean that some species have never been seen alive, and for many there is little information pertaining to their biology, reproduction, ecology, population size, or distribution. Most information of beaked whales comes from beach strandings.
Significance for Maori
No information specific to beaked whales was found, though it is likely that the bones of stranded beaked whales were used to form implements and ornaments. There are also references to the opportunistic harpooning of smaller species of beaked whales when encountered during sea voyages for fishing expeditions.
Key References
Folkens, P A, Reeves, R R, Stewart, B S, Clapham, P J and J A Powell. 2002. Guide to Marine Mammals of the World. National Audubon Society. Alfred A. Knopf Inc. 528pp.
Gaskin, D E. 1972. Whales dolphins and seals with special reference to the New Zealand region. Heinemann Educational Books Ltd. 200pp.
Hoelzel, A R (ed). 2002. Marine Mammal Biology: An evolutionary approach. Blackwell Science Ltd., Oxford. 432pp.
Perrin, W F, Würsig, B and J G M Thewissen (eds). 2002. Encyclopedia of Marine Mammals. San Diego: Academic Press. 1414pp.
Shirihai, H. 2002. The Complete Guide to Antarctic Wildlife: Birds and marine mammals of the Antarctic Continent and the Southern Ocean. Princeton University Press, Princeton, New Jersey. 510pp.
Table 10: Beaked Whales (Family Ziphiidae) in New Zealand
| Taxon | Common name | Status in New Zealand region | IUCN status | DoC status |
|---|---|---|---|---|
| Subfamily Ziphiinae | ||||
| Berardius arnouxi | Arnoux's beaked whale | Breeder | Lower risk-conservation dependent | Data deficient |
| Tasmacetus shepherdi | Shepherd's beaked whale | Unknown | Data deficient | Data deficient |
| 2 | ||||
| Subfamily Hyperoodontinae | ||||
| Hyperoodon planifrons | Southern bottlenose whale | Unknown | Lower risk-conservation dependent | Data deficient |
| Mesoplodon bowdoini | Andrews' beaked whale | Breeder | Data deficient | Data deficient |
| Mesoplodon densirostris | Blainville's beaked (dense-beaked) whale | Unknown | Data deficient | None given |
| Mesoplodon ginkgodens | Ginkgo-toothed beaked whale | Unknown | Data deficient | None given |
| Mesoploden grayi | Gray's beaked whale | Unknown | Data deficient | Data deficient |
| Mesoplodon hectori | Hector's beaked whale | Unknown | Data deficient | Data deficient |
| Mesoploden layardii | Strap-toothed whale | Breeder | Data deficient | Data deficient |
| Mesoplodon peruvianus | Pygmy beaked whale | Unknown | Data deficient | Data deficient |
| Mesoploden traversii | Spade-toothed whale | Unknown | Data deficient | Data deficient |
| Ziphius cavirostris | Cuvier's beaked (goosebeak) whale | Breeder | Data deficient | Data deficient |
| 10 |
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