Dolphin

Introduction.

Dolphin is a common name for the marine mammals of the infraorder Cetacea. There are about 40 species named as dolphin. Dolphin’s size range from 1.7m (5.6 feet) and 50kg (110lbs) to 9.5m (31 feet) and 10t (killer whale). Some dolphin species show sexual dimorphism. That means male animal is larger than female one. They have a streamlined body and limbs that are modified into flippers. Some dolphins can swim at a speed of 55.5km/h. They have well developed hearing. It is adapted for both water and air. Some species are adapted for diving to great depths. To keep the body warm in cold water they have a blubber (a fat layer) under the skin. The thickness of that layer depends on the climate. It also helps for the buoyancy of the animal.

Although dolphins are widely spread in the world most species prefer the warm waters of tropical zones. But also, some species prefer the colder climates.

Food habit.

Dolphins mainly feed on fish and squids. But some species like killer whales feed on large mammals like seals. Dolphins use their cone shape teeth to catch the fast swimming prey. Dolphins have a two-chambered stomach. It is similar to that of the terrestrial carnivores.

Reproduction.

The age of sexual maturity depends on species and gender. Usually male dolphins mate with more than one female every year. But females mate every two to three years. The gestation period differs with the species. Calves are normally born in spring and summer months. Female dolphins bear the responsibility of rearing claves.

Social behavior.

Dolphins are highly social animals. Usually they live in group of animals of dozen individuals. In areas of high food abundance, we can see many such groups live together. In such areas, there can be about 1000 dolphins. Membership in this groups is not rigid. Interchange is common. However, dolphins can create strong social bonds. They stay with injured or sick animals and, if needed they help these animals to breath by bringing them to the surface. Usually dolphins can create various sounds.

Man and dolphin.

From the past dolphin have been used as a symbol in various cultures. Dolphins have become themes in many literature and films. Dolphins are trained to perform various tricks. Bottlenose dolphins are frequently use for this purpose. Dolphin is considered as one of the most intelligent animal on Earth.

Threats to dolphins.

Dolphins have only few enemies. For most of small dolphin species Bull shark, Dusky shark, Tiger shark, and Great shark are a risk. Dolphins also suffer from various diseases and parasites. Some dolphin species are in a risk of extinction. Specially some river dolphin species like Amazon river dolphin, Ganges river dolphin and Yangtze river dolphin are critically endangered. From a survey conducted in 2006 found that there are no individuals of the Yangtze river dolphin, that means they are extinct from the Earth.

Hunting dolphins are common in countries like Japan. In addition to that by-catch, habitat destruction, marine pollution are main threats to them. Pesticides, heavy metals, plastic and industrial and agricultural pollutants that do not disintegrate rapidly in the environment concentrate in predators like dolphins. Injuries or deaths due to the collision with boats cause to the decrease of their population.

Measures taken to protect dolphins.

Dolphin safe labels are an attempt to confirm the consumer that fish and other marine products have been caught in a dolphin friendly way. As a result of the cooperation among marine activists and major tuna companies, first businesses with “Dolphin-safe” labels started in 1980s. It reduces the dolphin kills up to 50%.