Round head dolphin
| Round head dolphin | ||||||||||||
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Round-headed dolphin ( Grampus griseus ) |
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| Scientific name of the genus | ||||||||||||
| Grampus | ||||||||||||
| JE Gray , 1828 | ||||||||||||
| Scientific name of the species | ||||||||||||
| Grampus griseus | ||||||||||||
| ( G. Cuvier , 1812) |
The round-headed dolphin ( Grampus griseus ), also known as the Risso dolphin , is a species of dolphins (Delphinidae) named after the head shape that is unusual for the family. Today it is believed that the round-headed dolphin belongs to the relatives of the pilot whales ( Globicephala ) within the dolphins .
features
A round head dolphin can be almost four meters long and weigh a maximum of 650 kilograms. The most striking feature of this species is the unusual head profile: the round-headed dolphin has a voluminous, almost vertically sloping forehead with a distinctive melon , and the whale has a broad, but very short snout. Another characteristic is the sickle-shaped, large dorsal fin ( fin ), which resembles that of a young killer whale . The pectoral fins ( flippers ) are also very long and narrow, but only very slightly curved. The caudal fin ( fluke ) is wide with a deep indentation in the middle.
The round-headed dolphin has only two to seven teeth in the lower jaw and in the upper jaw there are only rudiments of stunted teeth. Sometimes the foremost pair of teeth or two can also be formed.
The round head dolphin is very variable in color. Calves are still silver-gray, then become darker and, as older young animals, are almost black with a few white spots on the belly side. Then the colors fade back to a slate gray. The colors stay strong longer on some parts of the body than on others. The resulting pattern is individually different. In addition, there are numerous scars in older animals , which result from both intra-species fights and from fights with other animals, such as cephalopods or sharks , and are more common in the males than in the females.
distribution
In all oceans , the round head dolphin can be found in both temperate and tropical latitudes. He also lives in the Mediterranean and the Red Sea . Its relatively low level of awareness is due to the fact that it rarely approaches the coast and stays away from ships. The northern limit of distribution is in the Atlantic at the level of Sweden and Newfoundland , in the Pacific off Alaska and the Kuril Islands . The southern border lies with South Africa , Tierra del Fuego , New Zealand and the southern coast of Australia .
In the European Atlantic and in the Mediterranean, especially in the Ligurian Sea , the round-headed dolphins occur regularly. They are very rarely found in the North Sea , they are absent in the Black Sea . One of the main gathering points for whales is off the Atlantic coast of the Iberian Peninsula , where they can be found in large numbers all year round. North of Great Britain they are only found seasonally, especially in late summer. The migration routes of the animals are not known for Europe. There appear to be food-borne migrations off the California coast.
Way of life
Like other dolphins, the round-headed dolphin forms groups ( schools ) that comprise on average 14 to 30 individuals, but can also contain up to 200 animals. Mixed groups with actual pilot whales ( Globicephala melaena ) were also observed. The animals probably prefer deeper waters, although entire schools could occasionally be observed in shallow bays. They use different tones to communicate , especially whistles.
The dolphins mainly eat cephalopods , and they rarely catch fish. The modifications of the skull as well as the reduction of the teeth are an adaptation to this form of nutrition, which is known as " teutophagy ". The exact composition of the food varies depending on the distribution area of the respective population, but the spectrum obviously includes almost all cephalopod groups. Hunting is usually not done by sight, but by echolocation .
Reproduction and development
The age at which round-headed dolphins become sexually mature has not yet been clarified. An indication, however, is the average length of the animals at this point in time, which suggests an age of slightly less than 13 years. In the Pacific as well as in the South and North Atlantic, the time of birth falls in summer. The gestation period is likely to be 13 to 14 months, so the mating season is in early summer.
The birth length of the whales is about 150 centimeters, according to other sources it is 120 centimeters. Nothing is known about the development of the animals or their maximum age.
Systematics
The round-headed dolphin was first scientifically described in 1812 by Georges Cuvier as Delphinus griseus . The skeleton of his holotype is now in the Natural History Museum in Paris . Since 1837 this species was placed in a new genus Grampus , in which it is the only representative to this day. A synonym of the species is Grampus richardsonii , which appeared in 1850 for the young of the species.
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Phylogenetic systematics of the Delphinidae according to Horreo 2018
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Today it is believed that the round-headed dolphin belongs to the relatives of the pilot whales (Globicephalinae) among the dolphins. This assumption is based primarily on features of the skeleton.
Genetic studies show the round-headed dolphin as the basal taxon of the pilot whale (Globicephalinae). According to current studies, they probably form the sister species of a taxon from the small killer whale ( Pseudorca crassidens ), the two known species of the pilot whale ( Globicephala ) and the broad-billed dolphin ( Peponocephala electra ) and the pygmy pilot whale ( Feresa attenuata ). Together these species form the subfamily Globicephalinae within the dolphins and are compared to the two species of the genus Orcaella .
Threat and protection
Like many other small whales , the round-headed dolphin is also regularly a victim of fishing , ending up in the nets as bycatch and usually suffocating painfully there. In Asia (Japan, Philippines) it is sometimes caught with nets or harpoons and ends up on the local markets, but its economic importance is very low compared to other species. So far, nothing is known about the impact of environmental pollution on these animals.
The round-headed dolphin is protected in all European countries and is listed in Appendix II of the Washington Convention on the Protection of Species . Import, transport and keeping are also prohibited by European Union legislation . There are no current inventory estimates.
supporting documents
- ↑ a b c d José L. Horreo: New insights into the phylogenetic relationships among the oceanic dolphins (Cetacea: Delphinidae). Journal of Zoological Systematics and Evolutionary Research 57 (2), May 2019; Pp. 476-480. doi : 10.1111 / jzs.12255
literature
- Mark Carwardine: Whales & Dolphins. Understand, recognize, observe . Gondrom, Bindlach 2005, ISBN 3-8112-2593-6 (high quality guide)
- Mark Carwardine: Dolphins. Biology, distribution, observation in the wild . Naturbuch Verlag, Augsburg 1996. ISBN 3-89440-226-1 (informative illustrated book)
- Ralf Kiefner: whales and dolphins worldwide . Year Top Special, Hamburg 2002. ISBN 3-86132-620-5 (guide of the magazine tauchen , very detailed)
- Tsuneo Nakamura: Dolphins . Chronicle Books, San Francisco, Calif. 1997. ISBN 0-8118-1621-4 (photo book on the subject)
- RR Reeves, BS Stewart, PJ Clapham, JA Powell: Sea Mammals of the World. A Complete Guide to Whales, Dolphins, Seals, Sea Lions and Sea Cows. Black, London 2002, ISBN 0-7136-6334-0 (guide with numerous pictures).
- Daniel Robineau et al. a. (Ed.): Wale and Delphine 1 . AULA-Verlag, Wiesbaden 1994. ISBN 3-89104-559-X ( Handbook of Mammals in Europe ; Vol. 6, Part 1-A; very detailed textbook)
- Gérard Soury: The great book of the dolphins. Delius Klasing, Bielefeld 1997, 2000. ISBN 3-7688-1063-1 (detailed illustrated book)
- Maurizo Würtz, Nadia Repetto: Underwater world. Dolphins and Whales . White Star Guides, Vercelli 2003. ISBN 88-8095-943-3 (identification book)
Web links
- Oceanlight.com - site with lots of photos of round headed dolphins
- Grampus griseus in the endangered Red List species the IUCN 2006. Posted by: Cetacean Specialist Group, 1996. Retrieved on 10 May, 2006.