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Striped Dolphin

Striped Dolphin

Stenella coeruleoalba

Physical description

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The striped dolphin is slender and streamlined with a well-defined beak. The beak is long and thin and there are about 50 cone shaped teeth on both jaws. The dorsal fin is placed mid-way down the body and is falcate. The pectoral fins are short and the tail fluke has a pronounced notch. Most noticeable are the two very well defined black or blue/black stripes, the first running form the corner of the eyes down to the anal region and the second from the eye to the pectorals. Sometimes these lines are double and there is usually a falcate area under the dorsal fin which also points to the eye. The fins, flukes, beak and jaws are all dark whereas the belly is pale.

Distribution
The striped dolphin is found in tropical and temperate waters of all oceans. In the Atlantic its northern limits are Newfoundland and Greenland. In the Pacific it is found as far North as Hokkaido or Washington. Southwards it is found all around Australia and New Zealand and South Africa as well as off the east coast of South America to the same latitudes. However on the west coast of South America it has not been found so far south. The striped dolphin prefers deep water and is rarely found in coastal areas. It carries out a local migration around the equator in the autumn, travelling towards the cooler latitudes in the spring.

Behaviour

Striped dolphins are very acrobatic, leaping up to 7 metres out of the water. They travel in very large groups of up to 100 individuals and are attracted by ships. Like many dolphins they enjoy bow riding but have a habit of suddenly “streaking” away from the ships. They can attain speeds of up to 37 km/hr, surfacing every five seconds. When travelling more slowly they surface roughly about every 10 to 20 seconds. There is no data at present about their use of sound.


Breeding
The large mixed schools of striped dolphins appear to be sub-divided into smaller breeding or non-breeding schools and mating is seasonal. The calving interval is thought to be about four years. Gestation lasts about 12 months and the young are between 93 and 100cm at birth. Females become sexually mature earliest, between 5 and 13 years, and the males between 7 and 15 years. Their maximum estimated age is 58 years.

Feeding
As one would expect from a species which has such a large range, the striped dolphin eats a large variety of foods. It seems to prefer feeding on shoals of small, deep sea fish, as well as squid and octopus. They can dive to depths of 200 to 700 metres but in the Atlantic their main prey seems to be cod.

Current situation

On a global scale the striped dolphin remains abundant. However, in some regions there is concern due to large numbers being killed in drift-netting for tuna and swordfish. Over fishing of their prey such as squid and cod seems to have led to striped dolphins being poorly nourished and therefore being more susceptible to disease. Around Japan the striped dolphin has been subjected to very intensive hunting in the past and they are seldom found in those waters now.