Every winter a bird survey is carried out by boat along the Meghna coast, and the writer has been taking part for almost 20 years. Besides birds, one aquatic animal is always seen: the Irrawaddy dolphin. More of these dolphins live along our coast than anywhere else in the world.

The dolphin everyone knows in the country's freshwater rivers is the shushuk. Go to a riverbank and you can see it leap up with a whoosh. Once there were shushuk in almost every freshwater river in the country; now they have fallen sharply. The Irrawaddy dolphin, however, survives in good numbers all along the coast.

Irrawaddy dolphins range most in the coastal rivers. In winter they come right into the rivers that link with freshwater rivers. Every year they are seen in the Bhairab-Rupsa Atai river. Every year a large group is seen on the way from Char Momtaz in Bhola to Sonar Char, and they also range well in the Bakkhali river on the way to Sonadia. The Sundarbans is the great sanctuary of the Irrawaddy dolphin: about 450 of them live along the Sundarbans coast and in its rivers, while 225 shushuk are seen there.

There is a river called the Irrawaddy on the coast of Myanmar, where fishers catch fish with the help of these dolphins. The fishers cast a net on one side of the river and ring a bell. Hearing the sound, the dolphins chase shoals of fish, which rush about near the net; some fish, blocked by the net, turn back, making them easy prey for the dolphins. In this way the fishers and dolphins of the Irrawaddy have lived side by side for ages, both gaining from it.

There is also a large group of Irrawaddy dolphins in the Mekong river in Cambodia, the place to see them up close. The writer spent a whole day with them in November 2016 and saw about 30 dolphins, which hunted in remarkable ways very close to the boat.

Of the world's 7,000 endangered Irrawaddy dolphins, 5,000 are found within Bangladesh. Dolphin research over the past ten years has taken the writer to rivers across the country, and it is now possible to estimate how many dolphins each river holds. Only the shushuk is seen along the whole Padma-Jamuna, where there are at least 50 important areas for it. About 1,500 shushuk are found in the country's rivers, one-third of the world total.

The dolphin is an indicator of a river's health: where there are more dolphins, there are more fish. Almost all the country's rivers leave dolphins unprotected. About 100 dolphins have died in the past four years, most of them caught in current nets. Although they live in water, they must surface to breathe every three to five minutes, so they die quickly if caught in a net. One study shows that about 78 per cent of dolphins that die are killed by getting caught in current nets.

The government has now taken steps to conserve dolphins. Three dolphin sanctuaries have been declared in the Padma-Jamuna and six in and around the Sundarbans. On the Meghna coast, the Nijhum Dwip Marine Reserve, the largest range of the Irrawaddy dolphin, has recently been declared.

Dolphin Day is observed around the world on 24 October to conserve freshwater dolphins; its main aim is to involve ordinary people in conservation. It has been observed in Bangladesh since 2018. Of the country's seven dolphin species, the shushuk is the only true freshwater dolphin, and it could become the national aquatic animal. The Irrawaddy is the chief animal of the coastal rivers. The writer hopes the dolphin, the life of the river, will fare well.

Source: Prothom Alo. First published in Bengali on The Agro News.