Overview

Brief Summary

The spade-toothed beaked whale may be the world's rarest whale. It was initially described in 1872 from a skull collected in the Chatham Islands, New Zealand. Other skull fragments were found on White Island, New Zealand in the 1950's and on Robinson Crusoe Island, Chile in 1986.   No live animals had been observed.  In December 2010, two whales presumed to be a mother and calf stranded and then died on Opape Beach, near to the White Island locality. Officials originally identified them as Gray's beaked whales, the most common beaked whale to strand in this area. Scientists took samples and photographs, then buried the bodies on the beach.  To everyone's surprise, DNA testing from those samples indicated that these were instead the elusive spade-toothed beaked whale.  Scientists have used the photographs to describe this whale's appearance for the first time.  They have also recovered most of the skeletal remains for further analysis.  (Thompson et al. 2012).

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Distribution

Range Description

The three specimens so far examined have come from New Zealand (White Island and the Chatham Islands [Pitt Island]), and Chile (Robinson Crusoe Island in the Juan Fernandez Archipelago). Therefore, this is probably a southern Hemisphere (possibly circum-Antarctic) species. However, it may be much more widely-distributed, and until more records are available, this will remain unknown (van Helden et al. 2002).
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Standing Distribution

Stranding Distribution

Appears to range through Eastern Tropical Pacific.

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Physical Description

Morphology

Tooth morphology

Tooth position

A single pair of large teeth overlap the posterior edge of the mandibular symphysis. The teeth recline posteriorly in long alveoli at an angle of 140 degrees.

Tooth exposure

In adult males, nearly all the tooth that erupts from lower jaw is exposed above the gumline. Teeth do not erupt above the gumline in females or juveniles.

Tooth shape

Broad and spade-shaped, the teeth of adult male M. traversii do not taper towards the tip as do the teeth of M. layardii. The teeth are weakly sinusoidal in the sagittal plane and the root is offset at about 20 degrees. There is a large prominent denticle on the apex of each tooth that is inclined forward with its tip facing outwards.

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Skull morphology

Diagnostic features of the skull and mandible

On the vertex of the dorsal skull the premaxillary bone extends forward of the nasal and frontal bones. Separates from Berardius and Ziphius.

A sulcus (groove) running along the middle of the combined surfaces of the nasal bones so depresses their combined middle that it is the lateral portion of each nasal bone that reaches farthest forward on the vertex. Separates from Tasmacetus and Indopacetus.

When the skull is upright and the long axis of the anterior half of the beak is horizontal, a horizontal plane transecting the summit of either maxillary prominence transects the mesethmoid bone. Separates from Hyperoodon.

Tooth alveoli of mandible overlap the posterior mandibular symphysis. Separates from Berardius, Ziphius, Tasmacetus, Indopacetus, Hyperoodon, M. densirostris, M. europaeus, M. ginkgodens, M. grayi, M. hectori, M. mirus, M. perrini, M. peruvianus, and M. stejnegeri.

Basirostral groove absent or present as a shallow groove that does not extend past the prominental turbercle. Separates from M. layardii.

The maxillary prominences rise 15+ mm higher than the height of the premaxillaries where the latter passes between the former. Separates from M. bidens.

The space between the nasals is extremely narrow. Separates from M. bowdoini and M. carlhubbsi.

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External morphology

Head Shape

Unknown.

Coloration

Unknown.

Size

Adult body length range unknown. Body length at birth unknown.

Most Likely Confused With:

Mesoplodon layardii

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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
Nothing is known of the habitat of this species. Nothing is known of the diet, but it is assumed that squid are the main prey.

Systems
  • Marine
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
DD
Data Deficient

Red List Criteria

Version
3.1

Year Assessed
2008

Assessor/s
Taylor, B.L., Baird, R., Barlow, J., Dawson, S.M., Ford, J., Mead, J.G., Notarbartolo di Sciara, G., Wade, P. & Pitman, R.L.

Reviewer/s
Hammond, P.S. & Perrin, W.F. (Cetacean Red List Authority)

Contributor/s

Justification
There is no information on abundance or trends in global abundance for this species. As a relatively uncommon species it is potentially vulnerable to low-level threats and a 30% global reduction over three generations cannot be ruled out (criterion A).

History
  • 2003
    Not Evaluated
    (IUCN 2003)
  • 2003
    Not Evaluated
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Population

Population
There is no information on abundance of this species. However, it is probable that it is relatively rare, given the small number of records of its occurrence so far discovered.

Population Trend
Unknown
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Threats

Major Threats
Direct hunting has never been associated with this species. Entanglement in fishing gear, especially gillnets is probably the most significant threat.

This species, like other beaked whales, is likely to be vulnerable to loud anthropogenic sounds, such as those generated by navy sonar and seismic exploration (Cox et al. 2006).

As a species potentially limited to temperate waters, the spade-toothed whale may be vulnerable to the effects of climate change as ocean warming may result in a shift or contraction of the species range as it tracks the occurrence of its preferred water temperatures (Learmonth et al. 2006). The effect of such changes in range size or position on this species is unknown.

Evidence from stranded individuals of several similar species indicates that they have swallowed discarded plastic items, which may eventually lead to death (e.g. Scott et al. 2001); this species may also be at risk.
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Management

Conservation Actions

Conservation Actions
The species is listed in Appendix II of CITES. Research is needed to determine the impacts of potential threatening processes on this species.
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Relevance to Humans and Ecosystems

Risks

IUCN Red List Category

Data Deficient (DD)
  • IUCN (2008) Cetacean update of the 2008 IUCN Red List of Threatened Species.
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Wikipedia

Spade-toothed whale

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The Spade-toothed Whale, Mesoplodon traversii, was a name given to a partial beaked whale jaw found on Pitt Island (New Zealand) in 1872 figured in 1873 by James Hector and described the next year by John Edward Gray who named it in honor of Henry Hammersley Travers, the collector. This was eventually lumped with the Layard's Beaked Whale, starting as early as 1878 (Hector 1878, who in fact never considered the specimen to be specifically distinct). A calvaria found in the 1950s at White Island (also New Zealand) initially remained undescribed but later was believed to be from a Ginkgo-toothed Beaked Whale (Baker & van Helden 1999).

In 1986, a damaged calvaria was found washed up on Robinson Crusoe Island (Chile), and was described as a new species, Mesoplodon bahamondi or Bahamonde's Beaked Whale. The results of DNA sequence and morphological comparisons (van Helden et al. 2002) have shown that all three finds come from the same species, which is therefore properly known as M. traversii. This species is remarkable since the external appearance is still completely unknown, and it is likely to be the most poorly known large mammalian species of our time.

Contents

Physical description

Nothing is known about this species other than cranial and dental anatomy. There are some notable differences between it and other mesoplodonts, such as the relatively large width of the rostrum; altogether it might look most similar to an oversized Ginkgo-toothed Beaked Whale in overall shape, as their skulls are quite alike except in size. The distinguishing character are the very large teeth of the animal, 23 cm (9 inches), close in size to those of Layard's Beaked Whale. The teeth are much wider than the Layard's, and a peculiar denticle on the tip of the teeth present on both species is much more pronounced in the Spade-toothed Whale. The common name was chosen because the part of the tooth that protrudes from the gums in life, unlike the straplike ones of Layard's Beaked Whales, must have a shape similar to the tip of a flensing spade of 19th-century whalers.

Despite the rather similar dentition, the Spade-toothed Whale and Layard's Beaked Whale seem only distantly related. The present species' relationships are not known with certainty though, because it is very distinct morphologically and DNA sequence information is contradictory and unable to propose a robust phylogenetic hypothesis this far[2]. Judging from the size of the skull, the species may be between 5 and 5.5 meters (16 and 18 feet) in length, perhaps a bit larger.

Ecology and status

This species has never been seen alive, so nothing is known of its behavior. It is presumably not different from other Mesoplodon of medium size, which are deep-water species living alone or in small groups and which feed on cephalopods and small fish. The young become independent of their mothers probably around one year of age, as in most whales.

The population status of the Strap-toothed Whale is entirely unknown, but it is unlikely to be abundant.

Specimens

  • NMNZ 546 - 1872; Pitt Island specimen. Apparently male, probably fully adult.
  • Auckland University School of Biological Sciences MacGregor Collection (unnumbered) - 1950s White Island specimen. Probably fully adult.
  • MNHNC 1156 - 1986; Robinson Crusoe Island specimen. Probably fully adult.

The sex of the 20th-century specimens is not known. However, by recovering or failing to recover DNA sequences of the Y chromosome, it could, in theory, be resolved. Note that little material is shared between the Pitt Island specimen and the calvariae, making direct anatomical comparisons problematic.

See also

References

  • Baker. Alan N. & van Helden, Anton L. (1999): New records of beaked whales, Genus Mesoplodon, from New Zealand (Cetacea: Ziphiidae). Journal of the Royal Society of New Zealand 29(3) :235–244. PDF fulletxt
  • Dalebout, Merel L.; Ross, Graham J.B.; Baker, C. Scott; Anderson, R. Charles; Best, Peter B.; Cockcroft, Victor G.; Hinsz, Harvey L.; Peddemors, Victor & Pitman, Robert L. (2003): Appearance, Distribution, and Genetic Distinctiveness of Longman's Beaked Whale, Indopacetus pacificus. Marine Mammal Science 19(3): 421–461. PDF fulltext
  • Gray, John Edward (1874): Notes on Dr Hector's paper on the whales and dolphins of the New Zealand seas. Transactions of the New Zealand Institute 6: 93–97. PDF fulltext. Although the paper was presented in 1873, it was not available in print until the next year.
  • Hector, James (1873) On the whales and dolphins of the New Zealand seas. Transactions of the New Zealand Institute 5: 154–170. PDF fulltext. Although the paper was presented in 1872, it was not available in print until the next year.
  • Hector, James (1878): Notes on the whales of the New Zealand seas. Transactions of the New Zealand Institute 10: 331–343. PDF fulltext. Although the paper was presented in 1877, it was not available in print until the next year.
  • Perrin, William F.; Wursig, Bernd & Thewissen, J.G.M (eds.) (2002): Encyclopedia of Marine Mammals. Academic Press. ISBN 0-12-551340-2
  • Reeves, Randall R. & Leatherwood, S. (1994): Dolphins, porpoises and whales: 1994-98 Action plan for the conservation of cetaceans. IUCN, Gland, Switzerland. ISBN 2-8317-0189-9
  • Reyes, J.C.; van Waerebeek, K; Cárdenas J.C. & Yáñez, J.L. (1995): Mesoplodon bahamondi sp.n. (Cetacea, Ziphiidae), a new living beaked whale from the Juan Fernández Archipelago, Chile. Boletin del Museo Nacional de Historia Natural, Chile 45: 31–44.
  • van Helden, Anton L.; Baker, Alan N.; Dalebout, Merel L.; Reyes, Julio C.; van Waerebeek, Koen & Baker, C. Scott (2002): Resurrection of Mesoplodon traversii (Gray, 1874), senior synonym of M. bahamondi Reyes, van Waerebeek, Cárdenas and Yáñez, 1995 (Cetacea: Ziphiidae). Marine Mammal Science 18(3):609-621. PDF fulltext

Footnotes

  1. ^ Taylor, B.L., Baird, R., Barlow, J., Dawson, S.M., Ford, J., Mead, J.G., Notarbartolo di Sciara, G., Wade, P. & Pitman, R.L. (2008). Mesoplodon traversii. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 24 March 2009. Database entry includes a brief justification of why this species is of data deficient.
  2. ^ Compare for example van Helden et al. (2002) and Dalebout et al. (2003).
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