Algae and plankton, a drought and heavy trawling in the upper reaches of the Tonle Sap are being blamed for the suffocation of 100 tons of fish since mid-April.
After complaints from fishermen that large numbers of fish were floating dead on the surface of the water, Kompong Chhnang province officials called a meeting with 11 fishing lot owners Wednesday to find a solution, said Ing Kim Leang, director of the agriculture and fishery office for the province.
Fishing lot owners have lost an estimated $100,000 since fish began dying in mid-April, he said.
Fish farmers’ heavy use of fertilizer in Kompong Chhnang province apparently led to a mass of algae and plankton in the water. In previous years, such large masses have been prevented by the monsoon rains, which disperse the fertilizer. This year’s fishing season, which kicked off in March and lasts through July, has seen little rain so far, leading to a build-up of the algae and plankton.
After algae and plankton bloom, they die, and the decomposition of the tiny plants and creatures begins to poison the water. Their remains create a cloud on the riverbed, where several varieties of bottom-feeding fish live. These fish swim to the surface in search of oxygen, where they are killed by the heat.
Compounding the problem, Ing Kim Leang said, is heavy trawling for freshwater shellfish like mussels, which are exported to Vietnam. Trawlers keep the silt on the riverbed from settling, which also pushes bottom-feeders to the surface.
“The water has become a green color because of the fertilizer in the water, which produces more plankton,” Ing Kim Leang said. “When the plankton in the water overheats, it converts into a poison chemical that drops into the mud, which [pushes out] the oxygen.”
The Ministry of Agriculture will send experts to the area to try to reduce the fish deaths, said Nao Thuok, director of the national fisheries department.
“Until now, we do not see any way to protect those fish,” he admitted Wednesday.
As a temporary measure, ministry officials have been asking fishermen to churn the water with their boat props, which will add some oxygen to the water, said Sam Nov, deputy director for the ministry’s fisheries department.
Sam Nov said that in past years, the rain has come sooner, bringing with it more wind and waves, which help keep the fish alive.
This year’s rainy season isn’t expected until mid-May, nearly three weeks from now, said Seth Vannareth, director of the meteorology department for the Ministry of Water Resources.
Temperatures in Kompong Chhnang have soared as high as 36.6 degrees, she said. “There will be a drought until mid-May,” she added.
The dead fish were of particular concern to fishing lot owners, who depend on the fishing season for their yearly wages. Fishing is illegal from July 1 to Oct 31, and it is difficult after the rainy season ends in November. The heaviest fishing takes place between March and June, when the water is the lowest.
Freshwater fish are one of the country’s top exports, according to the Ministry of Commerce. But the amount of fish sent to Thailand, the main importer of Cambodian fish, is unknown, according to Ted Knowels of the NGO Enterprise Development Cambodia.
He estimated that 100 tons of fish may pass through Poipet into Thailand in a single day.
Knowels said that while the algae and plankton may be economically harmful in the future, the tonnage of fish lost so far was not yet significant.
Chan Srieng, a fishing lot owner in Kompong Chhnang province, said she had been forced to sell dead fish—at a much lower price—because of the algae and plankton.
“I’m sad,” she said. “My fish prices dropped from 10,000 riel to 1,500 riel (about $2.50 to $0.38) per kilogram.”
Chan Srieng estimated that in April alone, 15 tons of fish died in her lot.
(Additional reporting by Brian Calvert)
