|Common Dolphin, Delphinus delphisCommon Names: Common dolphin, saddleback dolphin, criss-cross dolphin, hour glass dolphin or cape dolphin
General Description The common dolphin ranges in size from six to eight feet (1.8-2.4m). It is often hard to distinguish the common dolphin from other dolphin species such as the striped dolphin and the spinner dolphin. But, the common dolphin species can be identified by its hourglass color pattern. This hourglass design is made up of the colors white, gray, yellow and black. Young dolphins have color patterns that are lighter than their parents. The adult dolphin has a weight range of 155-245lbs (70-90kg). They contain two pointed pectoral flippers and a dorsal fin located on the center of its back. The dolphin’s dentition consists of 40-55, small sharp teeth located on each side of the upper and lower jaws. There are minimal differences between the male and female common dolphin. But there are however two different races of this species. They are the short beaked dolphin and the long beaked dolphin. Although the crucial differences between the races is the beak length, there are other distinguishing factors. The short beaked race has a wider body and a rounder head. The long beaked dolphin has a gently sloped forehead and a less complex beak. The most obvious sign of the presence of the common dolphin are the changes they inflict on the bottom topography. These alterations of the ocean’s floor are formed by the rapid herd movements of the animal.
Geographical Distribution and Habitat Requirements The common dolphin can be found in all five oceans of the world. The species tends to remain offshore where the ocean bottom is 590ft (180m) below the surface. It prefers tropical areas with warm temperatures. The optimum surface temperature for the common dolphin is usually between 50-82 degrees Fahrenheit (10-28 degrees Celsius). It also inclined to favor enclosed areas such as the Red Sea and the Mediterranean Sea.
General Biology The common dolphin can consume large amounts of food at time. In one day they can eat food quantities equal to nearly one third of their body weight. The dolphin is a slender and streamlined animal that can swim at speeds up to 19mph (30Km/h). The speed and endurance of the dolphin enables them to outdistance their prey. The diet of the common dolphin is primarily composed of octopus, squid, cod, hake and pilchards. Hunting by this species is done in groups that usually consist of 10 -500 members. However, groups with up to two thousand members have been sited in open waters. These groups appear to serve as a protective mechanism, as the groups form tighter assemblages when they are threatened.
The common dolphin is a highly active and extremely intelligent creature. They are a quick and aerobic species who engage in activities such as flipper slaps and bow rides. The dolphin also has the ability to hold its breath under water for extended periods of time. It usually remains underwater between 10 seconds to two minutes, before it breaks the surface to breathe through its blowhole. This blowhole is located on the top of the dolphin’s head.
Another distinguishing trademark of the common dolphin is its complex communication system. The dolphin is a very vocal mammal that emits both whistles and clicking sounds. These distinct noises are used by the dolphin to communicate alarm, sexual excitement and other emotions. The species also uses the clicking sounds for detecting prey. The dolphin releases clicking pulsations from a fatty area just below the blowhole called the melon. These sounds bounce off objects in the animal’s path and return to it in echos. These echos are used by the common dolphin to judge the distance and location of their prey. This phenomenon is referred to as echolocation.
The majority of knowledge on the reproduction of the common dolphin has been obtained through studies of captive individuals. This species usually mates during the spring months, and the male and female engage in courtship behavior before copulation. The gestation period for the common dolphin is around ten months and a single calf produced at birth. The new born is about 79-90cm in length and is capable of swimming to the surface within minutes of its delivery. The calve remains close to their mothers during the nursing period, which is believed to last between twelve and eighteen months.
Conservation The common dolphin has a secure conservation status. It is still found in a wide range of habitats and has not been identified by the ICUN as an endangered species. Certain populations of the common dolphin however, are threatened by human disturbances such as pollution, fishing nests and hunting. International tuna canners have recently refused to accept orders from fleets that do not attempt to protect dolphins. This restriction was adopted by tuna companies worldwide, after they received a great amount of pressure from both consumers and animal rights activists. The animal rights coalitions have also expressed concern about the treatment of common dolphins in public aquariums. Consequently, the Mammal Protection Act was passed in 1972 to prevent the mistreatment and exploitation of dolphins and other aquatic mammals.