Dolphins in Bangladesh

Dolphins are like mammals. They respire through their nostrils. They give birth to new babies and rear them until grownup. Their food items include small fishes, crustaceans, water insects etc. They live mostly in the estuary. Dolphins play an important role in the ecosystem. They can't live in the polluted water. So they indicate the pollution of the rivers. As they eat small fishes so they are also the indicator of fish abundance of that region. River erosion as well as huge numbers of vessel traffic affect their normal life. A great number of dolphins are found in the coastal belt of Bangladesh. The mixing process of freshwater with brackish water and leaves from the mangroves makes a favourable environment for different species of dolphin. The following seven types of dolphins are abundant here-

Ganges river dolphin or Shushuk (Platanista gangetica)

The Ganges River dolphin or shushuk is an "endangered", evolutionary ancient mammal that occurs in many rivers of Bangladesh. 

A rigorous survey in the Sundarbans mangrove forest indicates a population size of about 225 shushuks in these waters.

Irrawaddy dolphin (Orcaella brevirostris)

There are about 450 Irrawaddy dolphins in mangrove channels of the Sundarbans and about 5,400 in open estuarine waters of the Bay of Bengal. This is by far the largest population of the species recorded in Asia. The Sundarbans mangrove forest is the only place where the range of the shushuks and Irrawaddy dolphins overlaps. Both species are considered to be threatened with extinction in the near future.

Indo-Pacific humpback(Sousa chinensis)

Indo-Pacific dolphins are found in brackish waters of the Bay of Bengal and occasionally inside the Sundarbans mangrove forest. There is no estimate of population size but the large groups seen in Bangladesh up to 50 dolphins are encouraging.

Finless Porpoise(Neophocaena phocaenoides)

There are about 1,400 finless porpoises in coastal waters of Bangladesh with occasional sightings in the Sundarbans mangrove forest.

Indo-Pacific bottlenose dolphin (Tursiops aduncus)

A population of about 2,000 Indo-Pacific bottlenose dolphins lives at the head of the Swatch-of-No-Ground (Song), a 900 meter deep submarine canyon located only 40 km from the Sundarbans mangrove forest.

Spinner dolphin (Stenella longirostris)

Spinner dolphins are known for high leaps and spinning on their long axis. There is no estimate of population size but groups of more than 200 individuals are commonly seen in the Song.

Pan-tropical spotted dolphin(Stenella attentuata)

Pan-tropical spotted dolphins are found in groups of as many as 250 individuals in the Song. One group of around 800 spotted dolphins was seen feeding about 40 km offshore of Cox's Bazaar.

Article Source: Dhiman Gain

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