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Common Dolphin

Common Dolphin Illustration; Copyright Caroline Lathe

Physical Description

The distinctive yellowish hourglass pattern on the sides of a common dolphin makes it easy to identify. The back and upper flanks are black or brownish black; the chest and belly are cremy-white in colour, and there is a tan/yellow patch on the sides.  Flukes, flippers and dorsal fin are dark, and the beak is long and slim.  There are black stripes from the flipper to middle of the lower jaw and from the eye to the base of the beak.  Common dolphins measure between 1.7 and 2.4 metres, with the male slightly larger than the female.

Distribution

Common dolphins are found worldwide in temperate and tropical waters.  Widely distributed in British and Irish waters, mainly in the south and west and also in the North Sea, they are common in the southern Hebrides.  They appear to frequent deeper waters.  The Isle of Coll, Ardnamurchan Peninsula, occur between the months of June and July, but sightings have been reported up to late October.

Behavior


In British waters, these dolphins are usually found in groups of about 10 – 30 individuals, but sometimes in large, active schools of several hundred.  In the Pacific, schools can number more than 2000!  Their splashing can often be seen and heard from quite a distance.  They are fast swimmers, reaching speeds 24km per hour or faster if threatened.  Very acrobatic and boisterous, they leap clear of the water, with several individuals sometimes surfacing together.  Extremely vocal, their high-pitched squealing can be heard above the surface of the water.  Common dolphins are inquisitive and sociable, often approaching boats and hitching a free ride in the wake caused by the boat, an activity known as ‘bow-riding’.  To the delight of the passengers, they will often travel alongside a boat for several miles.

Feeding

The common dolphin has between 80 – 120 sharp, pointed teeth on each jaw, and eats a varied diet of squid and fish, such as cod, herring, and mackerel.  Individuals often co-operate to panic fish in order to catch them more easily.  They are often seen in association with diving gannets feeding on the same fish.

Current situation

These dolphins can live for up to 30 years.  As the name suggests, they are one of the most abundant cetaceans, numbered in millions worldwide, although some populations have declined due to exploitation.  The major threat they face is pollution, as well as accidental capture in fishing gear.