Nandikadal lagoon fish perished without oxygen, says NARA

Nandikadal lagoon fish perished without oxygen, says NARA

By Malaka Rodrigo

Thousands of fish seen floating in the Nandikadal and another nearby lagoon in Mullativu this week died because of a lack of oxygen, experts say.
Nandikadal is where a decisive battle against LTTE terrorism took place in May 2009. So the news of the dead fish triggered more curiosity.
The Fisheries Ministry directed the National Aquatic Resources Research and Development Agency to investigate. One June 4, a team led by NARA’s head of Environmental Studies S A M Azmi visited Nandikadal.

                         Sea of dead fish. Pic by Thayalan

“Different species of fish ranging from shrimp, eels to modha were found in the mass fish grave. We tested the water in the lagoon and found that the oxygen level is zero in the affected section of the lagoon. So literally, these fish died due to depletion of oxygen in the water,” Mr Azmi revealed.

They did not find any bacterial infection.
He also pointed out that this is a common phenomenon.
The water level of the Nandikadal lagoon had dropped below the sand bar as a result of the drought and this prevented the flow of water between the sea and the lagoon.

“Usually a sudden rain that brings lot of nitrogen and fertilizer to a water body triggers an algal boom – a rapid growth of microscopic algae. The algae soon die and the decomposition process consumes a lot of the oxygen dissolved in the water rapidly depleting the lifeline of the fish in the water. Once in a while fish in Beira lake and other inland water bodies, too, die due to this phenomenon according to the NARA expert. The area in Mullativu got some rains on the 29th of May, but there was little time for such algae bloom,” he said.

Mr. Azmi believes disturbances of the bottom sediments due to activities such as fishing could have triggered different oxygen consuming processes that led to the sudden depleting of oxygen in the Nandikadal lagoon. He said it is rarely that they record a zero oxygen level in a body of water, adding that even in cases of fish deaths in other areas due to low oxygen, the level is not zero.

The NARA team advised that a section of the sand bar be excavated to let the sea water flow into the lagoon.
Mr Azmi said the NARA team heard from locals that this is a common occurrence at this time of year. “So it is advisable to cut this barrier every year around the 15th of May,” Mr Azmi said.

This could happen in shallow coastal areas as well. These areas are called ‘dead zones’ resulting in deaths of fish in the open ocean as well.

Source – 11/06/2017, The Sunday Times, See more at – http://www.sundaytimes.lk/170611/news/nandikadal-lagoon-fish-perished-without-oxygen-says-nara-244783.html