CHENNAI: A day after the mass fish kill, scientists at the Central Marine Fisheries Research Institute (CMFRI), who conducted a preliminary investigation, say it was hypoxia that led to the loss of aquatic life.
Ecological hypoxia is a condition when the dissolved oxygen in water depletes alarmingly, taking a heavy toll on the marine life. According to a rough estimate, fish stocks worth about `10 have been wiped out. So what caused hypoxia?
Joe K Kizhakudan, scientist, CMFRI, told Express that this phenomenon occurs when there is a large aggregation of fishes in a smaller area. “During breeding season, species like mullets get into puddles in larger numbers and when there is a low tide, they get stranded in pools triggering hypoxia. The situation gets worse when there is an organic carbon load because of effluent release. The heavy organic load depletes the oxygen levels. In this case, our tests have shown that fish were under stress of breeding and when hypoxia condition kicked in, survival chances got reduced to zero per cent,” he said and added that the mortality numbers were huge.
Marine biologist Rahul Muralidharan said normally such fish kills don’t happen, but Chennai has a drainage system where lots of organic material are flushed into its rivers. The storm water drains, which take loads of illegal sewage, are connected during monsoon and flood the rivers. The first flood waters through the river mouth accumulate a lot of nutrient load near bar mouths, making it a perfect killing machine. “At present, except for mouth-breathing species like tilapia, no other fish species can tolerate the high pollution levels in the Adyar estuary,” he said.
CMFRI scientist said the minimum that can be done was to keep the bar mouth open allowing constant flushing. “Currently, the bar mouth is very shallow and during low tide, there is almost a zero exchange of water. Desilting of the bar mouth can mitigate the problem, to certain extent,” he said.
However, some environmental activists argue that silt deposition in the bar mouth is a natural phenomenon. During monsoon, the sand bar will be washed off in the strong currents. The main reason for the fish kill is the illegal discharge of sewer, which should be plugged. Many government institutions themselves discharge sewage into the Adyar river, claim activists.
Meanwhile, scenes are still palpable in Ururkuppam and Pattinapakkam fishermen hamlets dependent on the Adyar estuary for day-to-day living. When Express visited the villages on Wednesday morning, several fishermen were seen returning empty-handed. Karunakaran, a fisherman from Ururkuppam, said the entire fish stocks in the estuary had been wiped out. “I have laid nets four times and each time only plastic garbage is caught. Even during the high tide, the fish is not found,” he said.