BOATMAN Mohd Zambri Salleh, 42, regularly ferries anglers for fishing trips along Sungai Langat.
Early this year, he noticed that freshwater prawns in the river in Banting, Selangor were migrating to the riverbank en masse, to the extent that one could simply scoop them up by hand.
Locals term the phenomenon “udang mabuk”.
This is when the crustaceans are less active and swim closer to the surface.
“In my 12 years here, I have never seen prawns doing this,” he said when met in Kampung Olak Lempit.
Zambri expressed concern that industrial activities along Sungai Langat could have affected the river’s water quality.
“The prawn population boomed after movement restrictions were imposed in March 2020 probably because there were minimal human activities.Alwi Selamat, 43, from Kampung Labohan Dagang, who fishes at Sungai Langat regularly, however said it was not unusual.
“It can happen when the water temperature changes due to a downpour upstream.
“If there is pollution, then why aren’t fishes such as patin, keli and tilapia affected?” he asked.
Mohd Zambri opined that prawns were more sensitive to changes in water condition.
“Yes, it is normal for prawns to go ‘mabuk’ but not on the scale I witnessed recently,” he pointed out.
Badaruddin Paiku, 55, of Kampung Sungai Kelambu, said prawns sometimes swim closer to the riverbank during high tide, which carries more sediment.
“When the water recedes, the smaller ones are washed away while the big ones are left behind,” he explained.
Zambri did not think the incident was caused by “tuba” – which refers to illegal mass fishing using poison.
This is usually achieved by chopping off plants called “tuba” (Derris elliptica) before refining them into a powder.
The substance containing the chemical rotenone is then scattered in an area to kill fishes by blocking their respiratory systems.
While some might consider the phenomenon a blessing, Zambri does not.
“If this continues, the prawns might all die.
“Sungai Langat will lose its appeal and the income of boatmen like me will be affected,” he said.
Boatman Shahrul Surip said anglers could easily get between 1kg and 2kg of prawns during the phenomenon.
“Now that it is over, they may only get five or six prawns per fishing trip,” said the 43-year-old who rents out his boat for RM150 per day.
Badaruddin said past projects to straighten Sungai Langat had made the river shallower, causing the accumulation of debris and loose soil.
“When there is a downpour upstream, the water current will stir up the debris and cause the phenomenon,” he added.
Fisheries Department research institute senior director Dr Azhar Hamzah said the phenomenon was unusual.
“We were informed by the Environment Department (DOE) Sepang branch that there was a possibility of chemical pollution from nearby industies.
“This has affected the level of dissolved oxygen inside the river which caused the prawns to surface,” he said.
Azhar added that the Fisheries Department had released prawn larvae into Sungai Langat to increase its population.
Selangor DOE director Nor Aziah Jaafar said a check was performed along a 5km stretch of the river upstream from Kampung Labohan Dagang.
“We did not find any dead prawns and have taken 12 water samples to be analysed by the Chemistry Department,” she told StarMetro.
Environment and Water Minister Datuk Seri Tuan Ibrahim Tuan Man did not discount the possibility of “tuba” activity being the cause.
He also said that water run-off from the surface during a downpour could have reduced the level of oxygen in the river.
“Checks did not find any effluents. The public is advised to report any incidents to DOE,” he said in a post on his official Facebook page.
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