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. 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 tailstock 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. Field Identification: The most useful field identification features of the 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. Behaviour: 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. 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. Food and Feeding: Common dolphins feed on a wide variety of squids and fishes, particularly schooling fish such as herring and sardines. 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. 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. 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. More frequently seen off headlands during the summer but there is evidence of a strong inshore winter peak along the south coast, possibly associated with movements of sprat. In February 2001 common dolphins were observed on 9 days in groups ranging from 300-1,000 inside Cork harbour. Species Similar in Appearance: Most likely to be confused with striped dolphins, which differ only in markings. 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. Reproduction and Life Cycle: Max life expectancy: 25 - 30 years, Male sexual maturity: 5 - 12 years, between 1.7 - 2m, Female sexual maturity: 6 - 7 years, between 1.6 - 1.9m. Gestation period: 10 - 11 months, Calves born: Length at birth is 0.80 to 85 m and the calf is nursed for 14 - 19 months, although this may vary from stock to stock. 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 large unstained catches in fisheries. Stocks in the Black Sea, north eastern Mediterranean and the eastern tropical Pacific have apparently been depleted. Incidentally killed in some Atlantic fisheries and often stranded in large numbers along the Atlantic coast of France.
