Sudden large-scale death of fish in Dal Lake triggers panic

LCMA says mortality caused by thermal stratification; experts for proper scientific investigation
Sudden large-scale death of fish in Dal Lake triggers panic
Photo: Aman Farooq/GK

Srinagar, May 26: The sudden death of a large number of fish in Dal Lake following heavy spells of rain in the last two days has triggered panic among locals even as experts called for proper scientific investigation to ascertain the cause of mortality.

Locals were surprised to see a large number of small dead fish, mostly fingerlings, floating on the banks of Dal Lake.

“I was surprised to see hundreds of dead fingerlings on Dal Lake banks near Nishat,” said Abdul Hamid, a pedestrian.

Videos of floating dead fish went viral with netizens also expressing concern on the phenomenon giving different theories for mass death of fish.

Experts too expressed concern over the large-scale mortality of fish and called for comprehensive studies to ascertain the real cause of death.  

Dean Fisheries Sher-e-Kashmir University of Agricultural Sciences and Technology, Kashmir (SKUAST-K) Farooz Bhat said that during summer, there was a large Biochemical Oxygen Demand (BOD) and due to depletion of oxygen, some species of fish die.

“Such incidents have also taken place earlier in Dal and Nigeen lakes. If waters are stagnated or organic, waste level is high, and fish mortality can happen,” Bhat said.

Former Dean Fisheries SKUAST-K M H Balkhi said mass mortality of fish happens due to multiple factors like strong winds, acid rains, and dynamiting. “This one in Dal Lake seems to be the result of post-wind mixing up of bottom hypoxic waters with upper layers causing oxygen deficiency in the water column. Strong winds may have resulted in overturn of the water column resulting in mixing up of anoxic, hypoxic bottom waters with upper layers. Subsequently this leads to oxygen deficiency in water and instantaneous fish kill,” he said.

Balkhi said that the scientists from the Fisheries Department of SKUAST-K should investigate and analyse water and fish samples for confirmation.

“So far there is no need to panic. It is a natural calamity supported by humans by dumping organic wastes in water bodies, which settle down in the bottom and cause decomposition and anoxic conditions,” he said.

Some experts feel that extensive summer de-weeding could also cause depletion of dissolved oxygen because aquatic plants and weeds produce oxygen in the process of photosynthesis.

In 2012, hundreds of fish died in Nigeen Lake mainly due to change in physico-chemical parameters propelled by high pollution levels.

In 2010, death of fish in large numbers was witnessed in Wular Lake in north Kashmir.

Two species of fish Crossocheilus diplocheilus and Gambusia assinis are mainly affected in those water bodies, which have high concentrations of mosquitoes as they feed on their larva.

Experts said that the decomposition of organic matter causes hypoxic conditions in fragile water systems, leading to an increase in ammoniacal nitrogen, which is highly toxic for fish.

Earlier this month, capturing of a fish resembling the Alligator gar in the Dal Lake had set alarm bells ringing among the scientists who fear that the presence of non-native fish species could spell doom on the eco-fragile flora and fauna of the water body.

Ajaz Rasool, a noted environmentalist said, “Yes, there is a large-scale death of fish. We are witnessing a fish kill of fingerlings on the shoreline area from Oberoi Ghat upto Nishat Pipeline Bund at present.”

Elaborating, he said that these fingerlings were locally called ‘Thethur’ and Kashmir Latia in English and have the biological name of Crossocheilus diplocheilus.

“These fingerlings are very fragile and we have been witnessing fish kill of this type nearly everywhere in the Dal and Nigeen lakes sometimes in a year. Besides this there could also be multiple reasons responsible for such fish kill such as depletion of dissolved oxygen in lake water due to point source of pollution ingress, algal blooms in the lake water or any similar factor that may arise due to poorly handled maintenance procedures of private or public Sewage Treatment Plants (STPs) around the lake which is non-conducive for fingerlings to survive,” said Ajaz who has carried extensive studies on Dal and other water bodies.

He said that presently the Dal Lake was seen to be at high level on account of outflows from Chuntikul Channel to River Jhelum having temporarily stopped due to the river water being at higher level than the lake.

“However outflow from Nallah Amir Khan to Gilsar, Khushalsar and thereon to Anchar Lake is working to its capacity. The Dissolved Oxygen Level in this area to be tested is in the range from 4.5 mg/l to 6 mg/l, which is good for fish to thrive. Having seen such fish kills previously, the real cause needs to be ascertained by LCMA. As far as the quantum of fish kill is not alarming, it’s timely investigation for possible factors can help us handle the situation more effectively,” Ajaz said.

Some experts said that the fish deaths were caused by thermal stratification, which occurs when two types of steam with different temperatures come into contact.

The temperature difference causes colder and heavier water to settle at the bottom of the pipe while allowing the warmer and lighter water to float over the colder water.

Head of the Department Fish Genetics and Biotechnology SKUAST-K Irfan Khan said that the high nutrient load due to eutrophication, excessive weeds coupled with low oxygen seems to be the possible reason for fish kill.

“Harmful algal toxins can also complicate the situation and can be an addendum to the already present factors. Shallow lakes seldom stratify and can’t be a conclusive ground for fish kill,” he said.

Vice Chairman of Lake Conservation and Management Authority (LCMA) Bashir Ahmad Bhat told Greater Kashmir that the death of some fish species was likely caused by thermal stratification.

“There has been a fluctuation in temperature in the past few days. This is a natural phenomenon and has been observed in the past also. There is no need to panic. We rule out any death due to use of chemicals. We have collected samples and are analysing circumstances leading to the death of fish, mostly fingerlings. We are constantly monitoring oxygen levels at 17 places in Dal Lake and so far there is no depletion of oxygen. Dissolved Oxygen is more than six, which is good,” Bhat said.

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