Rampant pollution, using dredgers for lifting river sand, shallow water and plying of mechanized boats are sharply reducing the dolphin population in Halda river, Bangladesh’s largest natural breeding ground for carps.
According to Halda River Research Laboratory, at present, the number of river dolphins will not exceed 1,200. Of the total number, some 250 dolphins are found in the Halda river.
Regrettably, as many as 15 dolphins met unnatural deaths in the last three months in the Halda, posing a serious threat to the aquatic biodiversity.
On January 5, a dead dolphin weighing around 70kg was found floating in the river. Earlier on January 3, another dead dolphin weighing around 80kg was found floating in the same river. Both the dolphins had injury marks on their bodies.
The official status of the river dolphins, locally known as Shushuk [Platanista gangetica] is “critically endangered” as per the International Union for Conservation of Nature (IUCN) Red List.
The IUCN Red List of Threatened Species is a universally recognised index of the world's endangered animals.
Speaking to the Dhaka Tribune, noted Halda river researcher Prof Md Manzoorul Kibria said it was a matter of grave concern that dolphins were dying at regular intervals in the river.
He said: “There was a time when we used to come across dolphins frequently in the Halda river. It is very alarming that the number of dolphins is dwindling fast in the river due to anthropogenic or man-made hazards.
“A section of unscrupulous people are extracting sand through dredgers from the river, putting the existence of the dolphins at great risk. Recently, two dolphins died due to injuries from dredgers or propellers of engine-run boats.”
“It is time we take immediate steps to conserve the endangered aquatic mammals for the sake of aquatic biodiversity.
To this end, the Halda should be declared as a sanctuary for the river dolphins,” Kibria demanding adding that unplanned river dredging should be stopped without delay.
Prof Saidur Rahman Chowdhury, of Institute of Marine Sciences and Fisheries of Chittagong University, said: “The first condition for dolphin’s existence is clear and pollution-free water.
“Dolphins are called bio-indicators. So, the presence of great number of dolphins in a particular area is an indicator that the area has pollution free water.”
However, he said the untreated solid and liquid waste from industrial units and households were posing a serious threat to the aquatic ecological balance.
“The oil seeping from the vessels and engine-run boats is also posing threat to the dolphins. Moreover, the overfishing practice is creating food crisis for the aquatic mammals.”
Saidur said fishermen should stop the use of gill net as dolphins get entangled in it.
District Fisheries Officer Md Mominul Haque told the Dhaka Tribune that necessary steps would be taken to stop illegal river dredging.
Chittagong Department of Environment (DoE) in a report last year revealed that untreated effluent discharged from different industrial units, and households were polluting Halda river.
The report also placed a total of 12 recommendations to save the river from pollution.
The recommendations include earmarking the dredging spots as unplanned sand lifting raises the level of turbidity, imposing a ban on mechanized boats during the spawning and migration period of the fish.