Common Dolphin

Classification

Class: Mammalia
Order: Cetacea
Suborder: Odontoceti
Family: Delphinidae
Genus: Delphinus
Species: delphis
Common names: Short-beaked common dolphin
Irish Name: An deilf choiteann
 

Key Identification Features

Maximum body length: Adult male 2.6m, adult female 2.3
Average body length: Adult 1.7 - 2.4m
Head shape: Typical dolphin shape, eye ring and line from jaw to flipper
Beak: Black, long, teeth shape and conical, 80-100 Upper row, 80-100 Lower row
Dorsal fin: Tall, falcate, located mid-back. Often dark with a lighter centre.
Colouration: The beak, back and appendages are dark brown to black, and the ventral surface is white. The front flank patches are yellow and the rear flank and the sides of the tail-stock are streaked light grey. These features give a distinctive hourglass pattern on the sides, which is the most characteristic feature of common dolphins.
Markings: Distinctive black back and cape form a V-shaped saddle that dips below the dorsal fin. Hourglass pattern on sides. The eye is surrounded by black, and a narrow stripe runs forward to the melon. Another dark stripe runs from chin to flipper and several face to anus stripes may also be visible. Common dolphin © Pádraig Whooley, IWDG
 

Field Identification

The most useful field identification features of the short-beaked common dolphin are the yellowish/ochre patches on the sides in front of the dorsal fin and the V formed by the intersection of the different colours just below the dorsal fin.

Video Clip [MPG Format 5MB]
 

Species Similar in Appearance

Most likely to be confused with striped dolphins, which differ only in markings.
 

Behaviour

Short-beaked common dolphins are gregarious and live in herds ranging from a few tens to several thousands. They are active and boisterous and often bow-ride boats, ships and even large whales (fin whales in Irish waters). Breaching, surface slaps using the flippers not uncommon. They are often seen associated with other species. They are highly vocal, producing a wide range of whistles and pulsed sounds.
 

Status and Distribution

Common dolphins inhabit tropical to warm waters, generally preferring surface temperatures greater than 10°C. They are found mostly in relatively deep offshore waters, but some live in shallow coastal waters. They are found in the Pacific Ocean, Indian Ocean, Gulf of Mexico, Mediterranean, the Black Sea, the Red Sea, the Persian Gulf, Sea of Japan, the South China Sea and the Gulf of California. In the Atlantic, they occur from Newfoundland to Argentina and from Norway to South Africa.

Although no reliable estimates of world population exist, the common dolphin is undoubtedly one of the most abundant of all dolphins. They are split today into two forms, the long-beaked and the short-beaked common dolphin, but there is no overlapping of their ranges in the North Atlantic. 
 

Where and When Best Seen in Ireland

Although the biggest concentrations in Ireland are over the continental shelf and in deeper waters, they are frequently observed in shallow inshore waters off the south and southwest coasts and around the Aran Islands but also frequently seen in the southern Irish Sea and offshore.

Although frequently seen off headlands during the summer months, there is evidence of a strong inshore winter peak along the south coast, possibly associated with movements of sprat and herring. In February 2001 common dolphins were observed on 9 days in groups ranging from 300-1,000 inside Cork harbour. But aggregations of several hundred are not unusual from headlands that benefit from regular effort watches in Counties Kerry, Cork and Waterford.
 

Food and Feeding

Common dolphins feed on a wide variety of squid and fish species, particularly schooling fish such as herring and sprat. The diet varies seasonally in some areas. The schools adopt a number of different cooperative feeding strategies, including driving the shoals up to the surface where they are easier to feed, often attracting other predators, especially birds to the area. In other areas, they may feed at night, on organisms associated with the deep scattering layer.
 

Reproduction and Life Cycle

Max life expectancy: 25 - 30 years
Female sexual maturity: 6 - 7 years, between 1.6 - 1.9m
Gestation period: 10 - 11 months
Calves born: Length at birth is 0.80 - 0.85 m and the calf is nursed for 14 - 19 months, although this may vary from stock to stock.
Male sexual maturity: 5 - 12 years, between 1.7 - 2m
 

Social Structure

There is some evidence of sexual segregation in common dolphins, and of nursery schools, consisting of large proportions of pregnant and nursing females.
 

Conservation Issues

This species is one of several targets of directed fisheries in Japan and South America.

Despite its general abundance, certain stocks are in trouble; due mostly to unsustainable bycatch levels in certain fisheries. Stocks in the Black Sea, northeastern Mediterranean and the eastern tropical Pacific have apparently been depleted. Incidentally killed in some Atlantic fisheries and occasionally stranded in large numbers in European Atlantic waters, including the British Isles.
 

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