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Fishery experts say that it is unusual for such sea fish and other marine animals to come up to the estuaries along the coast. There have been only a couple of such precedents in the past, but never in such large numbers. Researchers say the 65-day embargo on fishing in the sea and other initiatives to protect fish at the river mouths, has improved the coastal environment, increasing the numbers of small fish and other feed for the larger fish. So the larger sea fish and other animals rush to the coast. However, this is the first time sailfish have come to the fresh water of the coast. There is need for study and research if this is indication of any big change in the sea environment.

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According to the Kuakata Dolphin Protection Committee, from January till 9 September this year, 15 dead dolphins came floating to the Kuakata sea beach. In August alone, 9 of these dead dolphins were beached. In the first 9 days of September, four dead dolphins washed up ashore. In the five months from January to June last year, the carcasses of 16 dolphins and 2 whales came ashore. Senior fisheries officer of Kalapara upazila, Apu Saha, said last year too around 7 to 8 dead dolphins floated to the coast near Kuakata.

After several dead dolphins were found along the shore at Kuakata, ECOFISH researcher Mohammad Ali went there and began looking into the cause of this phenomenon. He collected samples from the carcass of a dolphin. Speaking to Prothom Alo, Mohammad Ali said, "Large schools of Irrawaddy dolphins roam the area near the Sundarbans, stretching from the Swatch-of-No-Ground to Sonarchar. We are looking into the cause of their death. Primarily there seems to be three reasons behind the dolphin dying. These are, fishing even at a depth of 120 ft in the sea with trawlers, fishermen beating the dolphins to death when caught in their nets, and pollution."

Bangladesh habitat of Irrawaddy dolphins

According to experts, the Irrawaddy species of dolphins are gradually becoming extinct. Only 7000 or so remain alive today. And around 5800 of these are in Bangladesh. Bangladesh has become the largest shelter for the globally endangered Irrawaddy dolphin. Nowhere in the world are more than 200 of this species of dolphins seen together, other than in Bangladesh. This is because of the balanced proportions of salt and fresh water in the coastal rivers of Bangladesh.

It is high time to look into the cause behind the large sea fish and other aquatic animals coming to the coasts. If the marine ecology cannot be protected, the expansion, conservation, and increase of the country's fishery resources may come to a halt.

Forest department officers say that on 29 January 2012, the ministry of environment and forests issued a notification, declaring 47km of the routes of three rivers in the Sundarbans to be a dolphin sanctuary. Then on 27 October 2014, an area of 1738sq km along the north end of the Swatch-of-No-Ground was declared as a Marine Protected Area (MPA) for dolphins, whales, turtles, sharks and stingrays.

Dolphin researcher and professor of zoology at Jahangirnagar University, Md Abdul Aziz, told Prothom Alo, "So many deaths of dolphins is very alarming news. Our investigations at the spots show that many of the dolphins were caught in nets and died. But now this has become alarming. A large change in marine ecology is gradually becoming evident. This calls for extensive research. The government should take up a serious initiative for this immediately."

Captured sailfish

Shoals of sailfish are being caught in the Bay of Bengal over the past month or so. Researchers of ECOFISH-Bangladesh Project-2 of the international fishery research institute WorldFish, have observed that from the second week of August this year, the near extinct sailfish has been caught in Padma, Meghna, Jamuna and several other rivers of the country.

Between 15 and 26 August, 12,441 kg of fish was sold at the BFDC fisheries ghat in Cox's Bazar. On average every day, fishermen bring 10 to 40 sailfish to the ghat, ranging from 10 to 80kg in weight.

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This observation of ECOFISH is evident in other fishery ghats along the coast. From last August, a daily average of 15 sailfish is being brought to the BDFC fishery landing centre in Patharghata, the second largest fishery ghat of the country. On 26 August, 8 sailfish were caught by fishermen at Mahipur in Patuakhali.

The 55-year-old Siddique Jamaddar, helmsman of a trawler at Patharghata, has been catching fish at sea for the past 40 years. He said that in the past hardly one or two of these fish were caught. But now, even if hilsa isn't caught, these large sailfish are being caught in the nets more or less throughout the month.

Just like tigers leave the forest and come to human settlements when there is a food scarcity, aquatic animals also can relocate if there is an ecological crisis
Mr Mohammad Ali, assistant professor of the aquaculture department of Sher-e-Bangla Agricultural University and ECOFISH researcher

The International Union for Conservation of Nature (IUCN) in 2000 placed sailfish on its Red List. These fish basically live 50km radius from the coast. They are not very deep sea fish, but move around at a depth of 915 metres. They sometimes come near the coast, but do not enter the rivers. They can speed along at 110 to 130 km per hour. These speedy sailfish are better known as 'pakhi maach' (bird fish) in this country, probably because of the large fins on its back.

Stingray coming upstream

The stingray is another habitant of the sea like the sailfish. It is locally known as 'shapla pata maach' (lotus leaf fish). A stingray, over 13 maunds in weight, was caught on 30 August in a hilsa net in the river Jhunahar of Barishal. A 12 maund stingray was caught on 29 August in the Padma at Daulatdia.

Assistant professor of the aquaculture department of Sher-e-Bangla Agricultural University and ECOFISH researcher Mr Mohammad Ali, speaking to Prothom Alo, said, just like tigers leave the forest and come to human settlements when there is a food scarcity, aquatic animals also can relocate if there is an ecological crisis. Sailfish and stingrays are sea fish. This relocation can be because of a serious change in marine ecology and also due to an increase in manmade disturbances. Again, they may be rushing to the coast due to an increase in food at the river estuaries.

The researcher went on to say, if only a few such variety of fish were found in the rivers, this could be seen as an accident change in their route. But that probability is shrinking. This requires intensive research.

Director of Chattogram Fisheries, Sharif Uddin, told Prothom Alo, sailfish are very salty water fish. These cannot come to the fresh water of the rivers. Perhaps some over-enthusiastic fisherman has said these were spotted in the river. But catching sailfish in such large numbers at sea is abnormal. It should be seen whether this is the result of any large ecological change.

Bay of Bengal dead zone

The Guardian, on 31 June 2017, published an article, 'Bay of Bengal Depleted Fish Stocks and Huge Dead Zone Signal Tipping Point', written by to climate experts, Amitav Ghosh and Aaron Savio Lobo.

In the article they said that on May 2017, a multinational team of scientists reported an alarming finding – a very large “dead zone” had appeared in the bay. Apart from sulphur-oxidising bacteria and marine worms, few creatures could live in these oxygen-depleted waters. This zone already spanned some 60,000 sq km and appeared to be growing. The dead zone of the Bay of Bengal was at a point where a further reduction in its oxygen content could have the effect of stripping the water of nitrogen, a key nutrient.

With the reduction in oxygen, it would be difficult for the small aquatic animals like small fish, shrimps, other shellfish, crabs and so on to survive. They would move to other locations for the sake of reproduction and these would become extinct in these areas.

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Large fish live on small fish, shrimps and other aquatic life in the sea. The big fish go from one place to another to find food in face of food scarcity. This is when larger sea fish come towards the shore or the mouths of river.

Experts have said that pollution by plastics and other non-degradable substances or changes in rainfall, global warming and other reasons can be the reason behind the emergence of this dead zone.

It is high time to look into the cause behind the large sea fish and other aquatic animals coming to the coasts. If the marine ecology cannot be protected, the expansion, conservation, and increase of the country's fishery resources may come to a halt.

* This article appeared in the print and online editions of Prothom Alo and has been rewritten in English by Ayesha Kabir

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