Common dolphins are colorful, with a complex crisscross or hourglass color pattern on the side; the long-beaked common dolphin being more muted in color. 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.
Color patterns on the common dolphin are the most elaborate of any cetacean. The back is dark gray-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.
The common dolphin feeds on squid and small schooling fish. 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.
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 short-beaked common dolphins occur in the Southern California Bight.
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.
Traditionally, hundreds of thousands of common dolphins have been taken
incidentally, along with spinner and pantropical spotted dolphins, in purse
seine nets used during tuna fishing operations in the eastern tropical Pacific
although these numbers may be improving. Common dolphins also may be caught
accidentally in other fishing gear, such as midwater trawls. Turkish and Russian
fishermen used to catch large numbers of common dolphins in the Black Sea for
meat (to be used for fish meal) and oil. The fishery stopped after the common
dolphin numbers became severely depleted (and still is); there are several
reports suggesting that the Turkish fishery may have resumed. Many common dolphins
are taken in a Japanese small cetacean fishery and directly caught in the Mediterranean.
Some common dolphins may be taken in Peru for human consumption.