The Common Dolphin is the name given to up to three species of dolphin making up the genus Delphinus.
The most common of these dolphins are the Long Beaked Dolphin and the Short Beaked Dolphin. The third species (D. tropicalis, common name usually Arabian Common Dolphin), is characterized by an extremely long and thin beak and found in the Red Sea and Indian Ocean.
Common dolphins are also known by other names: Saddleback dolphin, White-bellied porpoise, Criss-cross dolphin, Hourglass dolphin and Cape dolphin. Despite its name the common dolphin is not the dolphin of popular imagination – that distinction belongs to the Bottlenose Dolphin, largely due to the television series’ Flipper’.
The common dolphin is widely distributed in temperate, sub-tropical and tropical waters throughout the world in a band roughly spanning 40 degrees south to 50 degrees north. Their preferred surface water temperature is 10 – 28 degrees Celsius. The sum population is unknown but numbers in the hundreds of thousands.
Characteristics of the Common Dolphin
Common dolphins have an hourglass pattern and tan or yellowish patch on each side which makes them easily recognisable, although they can sometimes be confused with Striped Dolphins. They have a dark cape ranging from black to brown with a v-shape under the dorsal fin. Their undersides are white with the occasional yellow streak and they have a white tail stock. Their flukes are dark on both sides and their dorsal fins range from curved to triangular and can be colored black, greyish white or somewhere in-between. There are only subtle differences between the males and females which sometimes makes it difficult to tell them apart.
Common Dolphins have a streamlined body and a long slender beak. They have a single blowhole and their flippers are pointed. Common dolphins are fast active swimmers.
When they are born, common dolphins are about 80 centimetres long (32 inches). Common dolphins can grow to be between 1.7 and 2.4 metres (5 feet 9 inches – 8 feet) in length.
Little is known about how much common dolphins weigh at birth, however, as adults, they weigh between 70 and 110 kilograms (155 – 245 pounds).
Common Dolphin Behaviour
Common dolphins travel in groups of around 10 – 50 in number and frequently gather into schools containing 100 to 2000 individuals. Their school size depends upon the time of day and season. When they are frightened, they bunch tightly together. Common dolphins are fast swimmers and enjoy acrobatics. These schools are generally very active – groups often surface, jump and splash together. Typical behaviour includes breaching, tail-slapping, chin-slapping, bow-riding and porpoising.
Common Dolphins do short dives of 10 seconds to 2 minutes, although dives of 8 minutes have been recorded.
Common dolphins have been seen to mix with other cetaceans such as other dolphins in the Yellowfin tuna grounds of the eastern Pacific and also schools of Pilot Whales. An interesting theory suggests that dolphins ‘bow-riding’ on very large whales was how they began to bow-ride on boats.
Common Dolphins are found in many enclosed seas and are rarely seen in waters less than 180 metres deep. In some areas, common dolphins are present all year round but other populations migrate seasonally. Common Dolphins can be observed regularly around the Galapagos waters.
Common Dolphin Diet
The diet of the Common Dolphin mainly consists of fish and squid.
Common Dolphin Communication
Common Dolphins are highly vocal and can be heard above the surface.
Common Dolphin Reproduction
The gestation period for the female Common dolphin is about 11 months and the calving period is between 1 and 3 years. Common dolphins become sexually mature at 5 years and their life span varies between 20 to 25 years. These figures are subject to large variation across different populations.
Common Dolphin Predators
Some sharks (including tiger sharks, dusky sharks, and bull sharks) and orcas will prey upon dolphins. Dolphins are also often trapped in fishing nets.
Common Dolphin Conservation
Common dolphins face a mixture of threats due to human influence. Populations have been hunted off the coast of Peru for use as food and shark bait. In most other areas the dolphins have not been hunted directly. Several thousand individuals have been caught in industrial trawler nets throughout their range. Common dolphins were abundant in the western Mediterranean Sea until the 1960s but occurrences there have tailed off rapidly.
The reasons are not well understood but are believed to be due to extensive human activity in the area. In the U.S. they are a protected species and sometimes are caught by accident in some trawler nets as bycatch, though despite this they are still quite common throughout their range.
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