Facts about Common Dolphin
The common dolphin (Delphinus delphis) is found in offshorewarm-temperate waters in
the Atlantic and Pacific and is the most
numerous dolphin within this range. It is closely related to the long-beaked common dolphin (Delphinus capensis) which prefers shallower
and warmer water. Short-beaked common dolphins are found in waters throughout New Zealand and Australia. In New Zealand, this species tends to remain a few kilometres from the coast and is particularly common in the Hauraki Gulf and off Northland.
Population
Common dolphins may form enormous schools of several thousand individuals. They are also known to associate with schools of pilot whales and other dolphin species such as dusky dolphins. This species is abundant but precise population estimates are largely unknown.
Diet and Foraging
Common dolphins feed on a variety of prey, including surface schooling fish species and small mid-water fish and squids. They are known to dive to depths of 280 metres in search of prey and hunt cooperatively within schools. Dives can last up to 8 minutes but are usually between 10 seconds and 2 minutes. These animals are vocal and show a wide range of acrobatic behaviour.
In some parts of the world, common dolphins feed at night on the deep scattering layer, which moves towards the water's surface during that time. Common dolphins have been seen working together to herd fish into tight balls. Like many other dolphin species, the common dolphin will sometimes take advantage of human fishing activities (such as trawling), feeding on fish escaping from the nets or discarded by the fishermen.
Life History
Gestation lasts for around 10-11 months and the calving interval varies from 1 to 3 years. Age at sexual maturity is estimated to vary with region but for the Pacific is thought to range from 7-12 years for males and 6-7 years for females. Maximum age is estimated to be 22 years.
Physical Description
Common dolphins are colourful, with a complex crisscross or hourglass colour pattern on the side; the long-beaked common dolphin being more muted in colour. When looking at the profile of the two common dolphin species, the short-beaked common dolphin has a more rounded melon that meets the beak at a sharp angle, as compared to the long-beaked common dolphin that has a flatter melon that meets the beak at a more gradual angle.
Surface characteristics
Colour patterns on the common dolphin are the most elaborate of anycetacean. The back is dark grey-to-black from the top of the head to the tail dipping to a V on the sides below the dorsal fin. The flanks are light gray behind the dorsal fin and yellowish-tan forward of the dorsal fin, forming an hourglass pattern. Its belly is white. There are large dark circles around the eyes connected by a dark line that runs across the head behind the beak and a black stripe runs from the jaw to the flippers.
Fins and Flukes
The dorsal fin is triangular-to-falcate (curved). It is pointed and located near the middle of the back and is black-to-light gray in color with a black border. The flippers are long and thin and slightly curved or pointed depending on geographical location. Flukes are thin and pointed at the tips with a slight notch in the center.
Length and Weight
Common dolphins can reach lengths of 7.5 - 8.5 feet (2.3-2.6 m) and weigh as much as 297 lb. (135 kg). The short-beaked common dolphin is relatively heavier, and has a larger dorsal fin and flippers than the long-beaked common dolphin.
Mating and Breeding
Sexual maturity is reached at 3 to 4 years of age or when they reach 6 to 7 feet in length (1.8 to 2.1 m). Calves are 30 to 34 inches at birth (76 to 86 cm ); gestation period is 10 to 11 months.
Distribution and Migration
The common dolphin is found in all tropical and warm-temperate waters. The long-beaked common dolphin is found more in coastal waters; the short-beaked common dolphin is found in offshore waters and is the species that occurs frequently in the eastern tropical Pacific. Both long-beaked and shortbeaked common dolphins occur in the Southern California Bight.
Natural History
Common dolphins are often found in large herds of hundreds or even thousands. They are extremely active, fast moving, and engage in spectacular aerial behavior. They are noted for riding bow and stern waves of boats, often changing course to bow ride the pressure waves of fast-moving vessels and even large whales. Common dolphins can be frequently seen in association with other marine mammal species.
