The predicament of the dead fish

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By 2017-06-18

By Risidra Mendis
Ceylon Today Features

Thousands of dead fishing floating on the water and washing ashore is not something we hear of everyday or so we think. But thousands of fish can suddenly die anywhere in the country if there is major water pollution in the waterways and lagoons. The recent incident of thousands of dead fish floating on the Nandikadal lagoon and washing ashore in the Mullaitivu area was attributed to polluted water by a team of National Aquatic Resources Research and Development Agency (NARA) specialists who visited the area.

Much to the surprise and shock of the fishermen in the Mullaitivu area they found thousands of dead fish washed ashore near the Nandikadal lagoon. While many reasons were initially attributed to the death of the fish, environmentalists came to the conclusion that this could be a warning sign of another tsunami about to hit Sri Lanka.

As soon as news got out that thousands of dead fish were washed ashore at the Nandikadal lagoon a team of officials from NARA visited the area to find out why the fish had suddenly died. Senior Scientist attached to the Environmental Studies Division NARA Dr. Niroshana Wickramarachchi told Ceylon Today that according to their investigations at the site the fish died due to water pollution and this type of incident could take place at anytime and anywhere in the country.

"The fish in the lagoon died due to a lack of oxygen. Some people say the fish dying are the signs of another tsunami about to happen. There is no connection between the death of the fish and a tsunami. The NARA team visited the area on 4 June 2017 and on 7 June 2017. On both visits we found out that the oxygen level in the water of the Nandikadal lagoon had gone down to zero. The Nandikadal lagoon is situated between the sea mouth and a bridge. We found that in between the sea mouth and the bridge there was a stretch of 2 km containing stagnant water. Due to the lack of oxygen in the stagnant water the salinity level in the water had increased and killed the fish," Dr. Wickramarachchi explained.

He added that the sea mouth had remained closed for around eight months and a barrier near the bridge had blocked the regular flow of water from the bridge to the sea mouth. "The sediments at the bottom of the sea cause the water to deteriorate. Due to the poor circulation of water the water can get polluted and cause the death of the fish. If there is stagnant water in any area it can cause the death of fish within three to eight months. Four milligrams per litre (the amount of oxygen dissolved) is the minimal level needed for better aquatic life. The peak time for the oxygen level to drop is from 2 a.m. to 7 a.m. because the fish, algae and other organisms consume oxygen at night. This is the reason for the oxygen level to drop drastically. When the sun rises the algae start giving out oxygen and the oxygen level in the water starts increasing. At 2 p.m. the oxygen level in the water is at its peak due to the algae giving out oxygen," Dr. Wickramarachchi said.

He goes on to say that if there is regular rain this type of water pollution will not take place because there will be a regular flow of water from the Nandikadal lagoon. "When the water flow is high the mouth of the lagoon will open due to the pressure of water and release the stagnant water to the sea. But if there is insufficient water in the Nandikadal lagoon the mouth of the lagoon will remain closed and the water will be stagnant. If the sediment level in the water body is high this type of incident can take place every two months. If polluted water flows from a canal to the lagoon the dying of fish can happen in a week," Dr. Wickramarachchi explained.

Commenting on the numbers of fish that died and washed ashore Dr. Wickramarachchi said five to ten lorry loads of fish were collected and buried on the beach by the relevant authorities. "The immediate solution to the problem is to increase the circulation in the water. NARA has instructed the Government Agent of the area to instruct the people to cut the mouth of the lagoon and allow the sea water to come in. This will cause a regular flow in the water and prevent such incidents from taking place in the future," Dr. Wickramarachchi explained.

Environmentalists also say the increase of fishing in the Nandikadal lagoon has caused the death of the fish. "When the number of fishermen increases they disturb the sediments at the bottom of the lagoon. When the sediments get disturbed they absorb more oxygen and the oxygen levels in the water go down resulting in a lack of oxygen for the fish. While a regular flow of water is needed to prevent the oxygen levels from dropping in the water and killing the fish in areas where fish breed it is up to the relevant authorities to ensure that no stagnant water remains in fish breeding areas," Environmentalists said.

Commenting on the sudden death of thousands of fish Ocean Resources Conservation Association (ORCA) Marine Naturalist Prasanna Weerakkody said there are many reasons why this could happen. "Pollution is generally the main culprit that causes the sudden death of thousands of fish if they are in a confined area. Climatic change can also cause the death of fish. The El Nino effect can cause the temperatures to rise suddenly in the water. In late December 2016 the sea water plummeted to very cold water. This type of effect can happen on a very large scale. In 1998 and 2016 the most significant events of such incidents was reported. In 1998 the cold temperatures in the water extended from the Maldives to Sri Lanka to India and up to Thailand from the other side of the world and were driven by a global climate change. Dynamiting of fish has also caused the death of hundreds of fish in the past," Weerakkody explained.

(Pix courtesy Dr. Niroshana Wickramarachchi)



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