Two-toothed whales

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Two-toothed whales
Sowerby's two-toothed whale (Mesoplodon bidens) on a Faroe Islands postage stamp

Sowerby's two-toothed whale ( Mesoplodon bidens ) on a Faroe Islands postage stamp

Systematics
Subclass : Higher mammals (Eutheria)
Superordinate : Laurasiatheria
Order : Whales (cetacea)
Subordination : Toothed whales (Odontoceti)
Family : Beaked whales (Ziphiidae)
Genre : Two-toothed whales
Scientific name
Mesoplodon
Gervais , 1850

The two-toothed whales ( Mesoplodon ) represent the species-richest genus of whales from the beaked whale family . Although 14 species have been described, particularly little is known about their biology. Since the two-toothed whales live in the open sea ( pelagic ), only a few sightings lead to a determination and can be evaluated.

distribution

Most species have a restricted range and occur in cooler or temperate oceans in the northern or southern hemisphere, only one species, the Blainville beaked whale , is found worldwide. In the eastern North Atlantic, and thus near the European coasts, live the true whale , the Sowerby two-toothed whale and the Gervais two-toothed whale .

description

Two-toothed whales are 3.5 to 6 meters long, depending on the species. They have a triangular fin placed far back . Namely, whales of this genus only have a fully developed pair of teeth in their lower jaw. In adult males these teeth (similar to the tusks of a boar ) are clearly visible even when the mouth is closed; in the case of long teeth (such as the Hubbs-beaked whale or the Layard whale ), the tips of the teeth protrude above the snout (rostrum) even when the mouth is closed . This suggests that these long teeth are also used when the mouth is closed. In juvenile males and females, the teeth are smaller and do not protrude. The tooth length has no influence on the size of the prey. In addition, there may be stunted rudiments of other teeth in the upper and lower jaw that are not assigned any function.

Way of life

Like all beaked whales, two-toothed whales dive very deep and hunt squids , which are their almost exclusive prey; in the Layard whale they accounted for 94.8% of the stomach contents in an evaluation, of which mainly Histioteuthis (Histioteuthidae) and Taonius pavo ( Gallertkalmare ).

Two-toothed whales live together in pairs or small groups. Suspicions that the groups were sexually separated were not confirmed.

Scars on the back and on the flanks of many male animals indicate that they are fighting intraspecific rivalry fights with their protruding teeth . There are no signs of interspecific fighting (investigated for Mesoplodon europaeus). There is no reliable knowledge about reproduction and gestation period. A calf is usually born in spring or early summer.

threat

No species of this genus was hunted on a large scale; there were simply too few sightings for that. The main threats are pollution of the seas and the fact that they are often caught in fishing nets and drowned. But the threat posed by sonar might also play a role, because after maneuvers with sonar tests, there were sometimes mass strandings. Population sizes or threat data are not available.

Identification of the species

The species often differ only in the size and position of the teeth, which is why it is very difficult to distinguish them during sightings - in females and young animals, whose teeth are not visible, it is actually impossible. But stranded, dead specimens are also repeatedly identified incorrectly. Sometimes only molecular-biological comparisons, e.g. B. their mitochondrial DNA (mtDNA). Quite a few species are not documented by a single unequivocal sighting and only by a few strandings.

The last described were the Peruvian beaked whale in 1991 and in 2002 the Perrin beaked whale , recognized as a separate species by molecular genetic studies . The Bahamonde beaked whale described in 1997 was found on the basis of mtDNA comparisons that the species is the same as in a skull found in New Zealand in the 19th century.

species

The compilation summarizes the species according to distribution area or tooth shape and does not necessarily reflect the relationships.

These three species are characterized by small teeth standing in front of the jaw and live in the North Atlantic, only the true whale has another population in the southern Indian Ocean .

These four species are restricted to the seas of the southern hemisphere ( South Pacific or circumpolar distribution).

This species, which lives in the Pacific and Indian Oceans, owes its name to its special ginkgo-like teeth.

These two species live in the northern Pacific and are characterized by large teeth in the back of the jaw.

  • Peruvian beaked whale ( M. peruvianus ) occurrence in the southeastern Pacific, first description 1991
  • Perrin-beaked whale ( M. perrini ) occurrence in the northeastern Pacific, first description 2002

These two species were described on the basis of stranding. They are the smallest members of their genus and, according to mtDNA comparisons, appear to be closely related to one another .

This species, sometimes in the subgenus Dolichodon , has the longest teeth of all species and lives in a circumpolar manner in the southern hemisphere.

A special feature of the Blainville beaked whale is its double sonar , otherwise unknown to toothed whales. Conspicuous curved lower jaws, on which the teeth sit, apparently in gender-typical expression , characterize this species, which is the only one in the world. Sometimes it is listed in the subgenus Dioplodon .

Was considered a synonym for M. ginkgodens for a long time and only became a valid species again in February 2014.

Individual evidence

  1. a b Merel L. Dalebout et al .: A divergent mtDNA lineage among Mesoplodon beaked whales: molecular evidence for a new species in the tropical Pacific? In: Marine Mammal Science , Volume 23, No. 4, 2007, pp. 954-966, doi : 10.1111 / j.1748-7692.2007.00143.x .
  2. a b c d S. K. Hooker, Robin W. Baird: Observations of Sowerby's beaked whales, Mesoplodon bidens, in the Gully, Nova Scotia. ( Memento of March 24, 2016 in the Internet Archive ) (PDF; 161 kB) In: Canadian Field-Naturalist , Volume 113, No. 2, 1999, pp. 273-277.
  3. ^ A b c d John E. Heyning: Functional morphology involved in intraspecific fighting of the beaked whale, Mesoplodon carlhubbsi. In: Canadian Journal of Zoology , Vol. 62, No. 8, 1984, pp. 1645-1654.
  4. a b c d e K. Sekiguchi, NTW Klages, PB Best: The diet of strap ‐ toothed whales (Mesoplodon layardii). In: Journal of Zoology , Vol. 239, No. 3, 1996, pp. 453-463, doi : 10.1111 / j.1469-7998.1996.tb05935.x .
  5. Colin D. MacLeod: Intraspecific scarring in odontocete cetaceans: an indicator of male 'quality' in aggressive social interactions ?. In: Journal of Zoology , Vol. 244, No. 1, 1998, pp. 71-77.
  6. ^ Stephanie A. Norman, James G. Mead: Mesoplodon europaeus. In: Mammalian Species. 2001, pp. 1-5. doi : 10.1644 / 1545-1410 (2001) 688 <0001: ME> 2.0.CO; 2 .
  7. Pamela M. Willis, Robin W. Baird: Sightings and strandings of beaked whales on the west coast of Canada. (PDF; 182 kB) In: Aquatic Mammals , Volume 24, No. 1, 1998, pp. 21-25.
  8. TM Cox et al .: Understanding the impacts of anthropogenic sound on beaked whales. In: Journal of Cetacean Research and Management , Volume 7, 2006, pp. 177-187.
  9. ^ Joseph Curtis Moore: Diagnoses and distribution of beaked whales of the genus Mesoplodon known from North American waters. In: Whales, Dolphins and Porpoises University of California Press, 1966, pp. 32-61.
  10. a b c Julio C. Reyes, James G. Mead, Koen Van Waerebeek: A new species of beaked whale Mesoplodon peruvianus sp. n. (Cetacea: Ziphiidae) from Peru. In: Marine Mammal Science , Volume 7, No. 1, 1991, pp. 1-24, doi : 10.1111 / j.1748-7692.1991.tb00546.x .
  11. a b c d Merel L. Dalebout et al .: A new species of beaked whale Mesoplodon perrini sp. n. (Cetacea: Ziphiidae) discovered through phylogenetic analyzes of mitochondrial DNA sequences. In: Marine Mammal Science , Volume 18, No. 3, 2002, pp. 577-608, doi : 10.1111 / j.1748-7692.2002.tb01061.x .
  12. ^ A b Anton L. Helden et al .: Resurrection of Mesoplodon traversii (Gray, 1874), senior synonym of M. bahamondi Reyes, Van Waerebeek, Cárdenas and Yañez, 1995 (Cetacea: Ziphiidae). In: Marine Mammal Science , Volume 18, No. 3, 2002, pp. 609-621. doi : 10.1111 / j.1748-7692.2002.tb01062.x
  13. ^ PT Madsen et al .: Biosonar performance of foraging beaked whales (Mesoplodon densirostris). In: Journal of Experimental Biology , Volume 208, No. 2, 2005, pp. 181-194, doi : 10.1242 / jeb.01327 .
  14. ^ M. Johnson et al .: Foraging Blainville's beaked whales (Mesoplodon densirostris) produce distinct click types matched to different phases of echolocation. In: Journal of Experimental Biology , Volume 209, No. 24, 2006, pp. 5038-5050, doi : 10.1242 / jeb.02596 .
  15. Joseph C. Besharse: maturity and sexual dimorphism in the skull, mandible, and teeth of the beaked whale, Mesoplodon densirostris. In: Journal of Mammalogy. 1971, pp. 297-315.
  16. Merel L. Dalebout, C. Scott Baker, Debbie Steel, Kirsten Thompson, Kelly M. Robertson, Susan J. Chivers, William F. Perrin, Manori Goonatilake, R. Charles Anderson, James G. Mead, Charles W. Potter, Lisa Thompson, Danielle Jupiter, Tadasu K. Yamada. Resurrection of Mesoplodon hotaula Deraniyagala 1963: A new species of beaked whale in the tropical Indo-Pacific. Marine Mammal Science, 2014; DOI: 10.1111 / mms.12113

Web links

Commons : Mesoplodon  - collection of images, videos and audio files