Blue and white dolphin
| Blue and white dolphin | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Blue and white dolphin ( Stenella coeruleoalba ) |
||||||||||||
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Stenella coeruleoalba | ||||||||||||
| ( Meyen , 1833) |
The blue and white dolphin or striped dolphin ( Stenella coeruleoalba ) is the most widespread species of the spotted dolphin ( Stenella ). It lives in all oceans in tropical , subtropical and temperate latitudes.
features
The blue and white dolphin is about 1.80 to 2.50 meters long and 110 to 165 kilograms. It has a very slim body and a narrow, short snout. The melon , i.e. the curve of the forehead, is clearly pronounced. The animals each have 36 to 45 pairs of teeth in the upper and lower jaw. Each tooth is tapered towards the tip and is slightly curved inwards.
The typical banding makes it easy to identify the animals and differentiate them from other dolphins : a black band runs from the eye to the front fins. Two more bands run from the eyes along the flanks and meet at the base of the tail under the belly. The area from the dorsal fin to the forehead is dark blue, the sides light gray and the ventral side mostly white. The tail section is completely dark in color from the anus on.
The dark dorsal fin is concave at the back and lies roughly in the middle of the back, the pectoral fins are curved and the caudal fin ( fluke ) is indented in the center.
distribution
The blue and white dolphin can be found in all warmer seas worldwide. In the west pacific he swims very often off the coast of Japan , there is also evidence from the central pacific from the coasts of Hawaii , from Papua New Guinea and the Solomon Islands . On the American Pacific coast you can meet the striped dolphin up to 50 degrees north latitude .
In the Indian Ocean , the animals are found off the coasts of Mozambique and South Africa . Their distribution here is likely aided by the Agulhas Current , which carries warm seawater along the south coast of Africa.
The northern limit of distribution in the Atlantic is probably at the level of Nova Scotia ; the northernmost evidence comes from the south coast of Greenland , although it was probably just a lost specimen. In the Southwest Atlantic you can find dolphins along the coast of South America , and in the central Atlantic near Jamaica and Ascension . On the African Atlantic coast it occurs north of Senegal to the Mediterranean Sea , and also on the southern European coast of Spain , Portugal and southern France . From around Gascony , the frequency of the animals decreases significantly. However, there are also sighting reports and stranded animals from the Netherlands and Great Britain .
In the western Mediterranean, the blue and white dolphin is probably the most common dolphin species after the common dolphin ( Delphinus delphis ), with which it is very often confused here. The animals are also less common in the eastern Mediterranean.
Way of life
Blue and white dolphins are very active. They often soar out of the water and "ride" on the bow waves of ships or migrating large whales . Your communication consists of clicks and whistles.
The observations on the dolphins lead to the conclusion that these animals make seasonal migrations. They usually appear off the coast of Japan in September to October and then move to the East China Sea to winter . The return hike takes place in spring with a somewhat greater distance from the coast. This migration is likely to be influenced by the warm Kuroshio Current . Migrations are also assumed for the populations off the European coast. The assumption is based on the fact that most beachings on the coasts of Spain take place in spring and summer, whereas in France it occurs in winter. For this reason, a northward migration is assumed for wintering, which is probably linked to the availability of food.
The blue and white dolphins live in groups of around 25 to 1000 animals and form so-called schools. They prefer the marine area a little further away from the coast and rarely approach it more than 200 meters.
The food of the animals consists almost exclusively of cephalopods and small to medium-sized fish in the open water, as well as crustaceans , which they bring in from a depth of up to 200 meters. As with other small whales , sharks and killer whales can be seen as natural enemies for the blue and white dolphin .
Reproduction and development
The females of the blue and white dolphins reach sexual maturity in different regions around an age of six to seven (Mediterranean) or nine to ten years (Japan), the males around a year earlier. The males do not mate until around 12 to 16 years of age, after they have reached "social sexual maturity". The females carry a young about every three years, the pregnancy lasts about 13 months, the lactation period about 16 months and the subsequent mating break about 6 months. After the age of 30, pregnancies decrease significantly.
There is no information about the mating behavior of these dolphins. The mating times and thus also the times of birth are regionally different. Births in the Mediterranean fall from autumn to the beginning of winter, while two birth periods are given for the Northeast Atlantic, spring and autumn.
The smallest young animal found so far was 80 centimeters long, the largest fetus 108 centimeters. It is believed that the average length of newborns is about three feet. After birth, the young animal is suckled for 12 to 16 months. Blue and white dolphins can reach an age of over 40 years, the oldest animal found so far was estimated to be 57 years old.
Systematics
In addition to the blue and white dolphin, the genus of the spotted dolphin contains four other species, all of which have a much smaller distribution area. These are the East Pacific dolphin ( Stenella longirostris ), the Clymene dolphin ( Stenella clymene ), the slender dolphin ( Stenella attenuata ) and the bridle dolphin ( Stenella frontalis ). A phylogenetic study of these species is not available.
For the blue and white dolphin, various subdivisions into subspecies have been discussed, but all of them have proven to be unsustainable. There are, however, variations in color and size between different populations.
Threat and protection
The worldwide population is estimated at over two million individuals and is not threatened, for this reason the animals are not protected separately. However, regional problems can arise. The population of animals in the Mediterranean has dwindled, especially due to deaths in ship propellers and fishing nets. In Japan, especially off the Izu Peninsula , near Chōshi and near Taiji , blue and white dolphins were shot in large numbers for a long time, around 14,000 specimens annually in the 50 / 60s. In the 1980s a quota of 1000 dolphins per year was introduced, which caused the species to recover somewhat in the Northwest Pacific. This quota is still valid today.
As with many other whales also provides for the blue-white dolphins marine pollution by environmental toxins , the main burden. Especially heavy metals such as mercury , lead or cadmium accumulate in the whales in the muscles and the liver and in the kidney to. Fat-soluble environmental toxins such as polychlorinated biphenyls (PCB) or (now decreasing) dichloro-diphenyl-trichloroethane (DDT) accumulate in the fat layer .
In the early 1990s, the Mediterranean population was also seriously threatened by a viral infection . This started in 1990 from the Spanish coast and spread to the eastern parts of the Mediterranean by 1992. The trigger was probably a morbillivirus , which mainly killed weakened animals with very high concentrations of heavy metals. The number of animals that died within these two years is estimated to be well over 1,000.
literature
- Mark Carwardine : Whales and Dolphins. Delius Klasing, Bielefeld 2008, ISBN 978-3768824736 (high quality guide)
- Mark Carwardine: Dolphins. Biology, distribution, observation in the wild. Naturbuch, 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)
- J. Niethammer, F. Krapp (ed.): Handbook of mammals in Europe. Vol 6. Marine mammals. T 1a. Wale und Delphine 1. Aula, Wiesbaden 1994, ISBN 3-89104-559-X (very detailed textbook)
- 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).
- Gérard Soury: The great book of the dolphins. Delius Klasing, Bielefeld 1997, ISBN 3-7688-1063-1 (detailed illustrated book)
- M. Würtz, N. Repetto: Underwater World. Dolphins and Whales. White Star Guides, Vercelli 2003, ISBN 88-8095-943-3 (identification book)
- T. Nakamura: Dolphins. Chronicle Books, San Francisco 1997, ISBN 0-8118-1621-4 (photo book)
Web links
- Blue and white dolphin
- Stenella coeruleoalba in the endangered Red List species the IUCN 2006. Posted by: Cetacean Specialist Group, 1996. Retrieved on 11 May, 2006.
Individual evidence
- ^ T. Kasuya, N. Miyazaki: The Stock of Stenella coeruleoalba off the Pacific Coast of Japan . In: Food and Agriculture Organization of the United Nations (Ed.): Mammals in the seas . Volume IV: Small Cetaceans, Seals, Sirenians and Otters. Rome 1982, ISBN 92-5100514-1 , pp. 21 ( limited preview in Google Book search).