Sowerby's two-toothed whale
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Sowerby's two-toothed whale ( Mesoplodon bidens ) |
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| ( Sowerby , 1804) |
The Sowerby two-toothed whale ( Mesoplodon bidens ), also known as the North Sea beaked whale or flosser , is a species of whale from the beaked whale family (Ziphiidae). This was discovered in 1804 as the first whale species from the genus of the two-toothed whale and was named after its first describer James Sowerby .
distribution
The Sowerby two-toothed whale is distributed over large parts of the northern Atlantic . In the west it ranges from Labrador to New England ; however, the focus of their occurrence is the eastern Atlantic, where the animals are widespread on the European and North African Atlantic coasts from Iceland , Great Britain and Ireland as well as Norway to Madeira and the Azores . They are also found in the North Sea and possibly also in the eastern Mediterranean , where the species has only been found once documented.
With more than 150 strandings, most of them off the British Isles , the species is one of the best-documented species in its family, but sightings of live animals are rare, as with all two-toothed whales.
description
Sowerby's two-toothed whales can reach a length of around 4.5 to 5.5 meters and a weight of up to 1.5 tons. The body of the animals is spy-shaped with the largest diameter around the middle of the body. They are colored dark blue, dark gray or almost black on the upper side, the underside and the flanks are lighter. Elderly males' bodies may be covered in long, unpigmented scar lines that stem from rivalry battles. The snout area and the lower jaw form a beak-like long snout. In adult males, two triangular and tusk-like teeth protrude from the lower jaw; in females and young animals, these are not visible when their mouths are closed. In the area of the throat there are two clear pits. This whale species has very small flippers and a small, crescent-shaped fin , which, like all beaked whales, sits far back on the body, the relatively wide fluke is curved at the edge and has no central notch. The tail stalk is flattened laterally.
Way of life
These whales are inhabitants of open and deep sea areas. They prefer areas with a water depth of 500 to 2000 meters, usually in the area of highly structured seabed regions, submarine mountains and on the continental slope. The animals live mainly in colder water areas with maximum temperatures of up to 15 ° Celsius. There are different details about the group size. In addition to sightings of animals living in pairs (and stranding in pairs), there have also been reports of schools consisting of three to ten animals, including several males. It is assumed that group sizes of up to 10 animals exist, but most schools contain a maximum of 5 animals.
The whales mainly eat smaller squids and fish that live in the deep sea and on the seabed . The Sowerby two-toothed whale is one of the few species for which it is documented that the proportion of fish in the food spectrum is greater than that of deep-sea squid. They prefer fish species in the deeper pelagial and benthic zones, including cod that live in the deep sea . The prey animals reach lengths of 1 to 6% of the body length of the whales, most of them between 2 and 3%. Depending on the food spectrum, the hunt mainly takes place at greater depths of the sea, assuming a water depth of 500 to almost 3000 meters. The dives can last over an hour before the whales come to the surface to breathe.
Male animals are easy to recognize by their scars on their backs and flanks. These scars come from rival fights that the animals fight with their excellent teeth. As with all beaked whales, hardly any information is available about the mating and reproduction of the animals. It is assumed that matings and births are seasonal and that after a gestation period of about 12 months, births take place in spring.
Systematics
The Sowerby two- toothed whale is an independent species of the two- toothed whale ( mesoplodon ) within the toothed whale . It was described in 1804 by James Sowerby on the basis of an individual who stranded on the Scottish coast near Elgin as a physeter bidens and thus assigned to the sperm whales . 1817 described Henri Marie de Blainville Ducrotay with Delphinus sowerbensis another way, on the basis of the description in 1850 and establishment of the separate genus Mesoplodon by Paul Gervais took place. Delphinus sowerbensis was later synonymous with Physeter bidens , making the Sowerby two- toothed whale the type species for the genus.
No subspecies are distinguished within the species.
Danger
Due to the very little data on the populations and population developments of the animals, the Sowerby two-toothed whale is not assigned to a hazard category by the IUCN , but is listed as "data deficient". The species is not believed to be critically endangered, but it may be endangered. They are not threatened by commercial whaling , even though individual animals have been killed by whalers in the past. However, they are probably occasionally caught in fishermen's nets as bycatch .
In the last few years in particular, the influence of underwater noises, especially from sonar used underwater and explosions on various whales, including beaked whales, has been examined and discussed. There is clear evidence that these noise emissions have an impact on whales and lead to stranding of dolphins and beaked whales, among others. To what extent these emissions affect the Sowerby two-tooth whale is not known, but it can be assumed that it is also affected. In addition, plastic remains were found in various stranded whales, which were also discussed as a specific cause of death in individual cases.
The Sowerby two-toothed whale is listed on Appendix II of the Washington Convention on the Protection of Species (CITES).
supporting documents
- ↑ a b c d e f g h i "Sowerby's Beaked Whale." In: CD MacLeod: Family Ziphiidae (Beaked Whales) In: Don E. Wilson, Russell A. Mittermeier: Handbook of the Mammals of the World. 4. Sea Mammals. Lynx Edicions, Barcelona 2014; P. 356. ISBN 978-84-96553-93-4 .
- ↑ a b c Mesoplodon bidens . In: Don E. Wilson , DeeAnn M. Reeder (Eds.): Mammal Species of the World. A taxonomic and geographic Reference. 2 volumes. 3. Edition. Johns Hopkins University Press, Baltimore MD 2005, ISBN 0-8018-8221-4 .
- ↑ a b c d e Mesoplodon bidens in the endangered Red List species the IUCN 2006. Posted by: BL Taylor, R. Baird, J. Barlow, SM Dawson, J. Ford, JG Mead, G. Notarbartolo di Sciara, P. Wade, RL Pitman, 1996. Retrieved May 23, 2020.
literature
- "Sowerby's Beaked Whale." In: CD MacLeod: Family Ziphiidae (Beaked Whales) In: Don E. Wilson, Russell A. Mittermeier: Handbook of the Mammals of the World. 4. Sea Mammals. Lynx Edicions, Barcelona 2014; P. 356. ISBN 978-84-96553-93-4 .
Web links
- Mesoplodon bidens in the endangered Red List species the IUCN 2006. Posted by: BL Taylor, R. Baird, J. Barlow, SM Dawson, J. Ford, JG Mead, G. Notarbartolo di Sciara, P. Wade, RL Pitman, 1996 Retrieved May 23, 2020.