The Halda river, the country's largest natural breeding ground for carps, has been under constant threat due to manmade hazards, including industrial waste, sewage contamination and sand extraction.
The situation has gotten worse owing to a rapid increase in tobacco farming near the river in recent years, which threatens the unique biochemical properties of the water that supports the existence of these fish.
Also, setting up of a rubber dam on the river's upstream disrupts its natural flow.
This season, carps have released an almost negligible amount of spawns, which experts term an alarming sign for their continuing existence.
Originating from Halda Chora of Ramgarh upazila under Khagrachhari, the 98km river flows through Fatikchhari, Hathazari and Raozan upazilas and Chandgaon Thana in Chittagong city, and falls into the Karnaphuli river.
Halda is a unique river as it is the lone natural breeding ground for carps (ruhi, katol, mrigal etc). Due to the unique biochemical properties of its water, carps choose it as a safe haven to release spawns there.
But the manmade hazards now threaten the natural habitat of these fish, experts said.
According to researchers and spawn collectors, 210kg of spawns were collected in 2011 while the amount was 354kg in 2012, 70kg in 2013, 275kg in 2014, 47kg in 2015, and 12kg in 2016.
However, the data differed significantly from that of the Department of Fisheries (DoF), according to which, 326kg of spawns were collected in 2011, 1,569kg in 2012, 612kg in 2013, 508kg in 2014, 156kg in 2015 and 168kg in 2016.
The Daily Star talked to some spawn collectors to get a clear picture of the discrepancy between the data collected by the researchers and DoF.
Kamal Uddin Sawdagaor has been involved in collecting spawns for around 45 years. He said although carps released spawns three times last year from March to May, it was not on a large scale.
“I engaged six boats for three months in the river but collected just 1.8kg of spawns whereas it was 7kg the year before,” said the 65-year-old. “Approximately 80 percent of the around 250 boats returned almost empty-handed, while in the 90s I used to collect over 40kg of spawns.”
When asked what would be the total amount of spawns in 2016, Kamal said it would not be more than 12kg to 15kg. When told the DoF data says 168kg was collected, Kamal said that “could not” be true.
Another spawn collector Harech Shah's account was almost the same.
Harech said he engaged six boats in 2016 but collected just 1.95kg of spawns. “I invested Tk 95,000 but was able to make only Tk 41,000 by selling spawns.”
He said the DoF data could not be true since most of them did not get an adequate amount of spawns last year.
“Tobacco cultivation on a large scale over the last few years on the river's upstream land is a major reason for carps not releasing an adequate amount of spawns,” said Halda researcher Dr Manzoorul Kibria.
“It has been found in research that tobacco leaf is poisonous for fish,” he said, adding, residues of the toxic plants and excessive pesticide from farmlands are flowing into the carp-breeding Halda river threatening its very existence. But eyeing more profit, the farmers continue to cultivate tobacco, he said.
Manzoorul, an associate professor of zoology at Chittagong University, said industrial discharges are also polluting the river.
At the same time, the establishment of a rubber dam without conducting any environmental impact study is disrupting the river's natural flow, he emphasised.
He said around 70 years ago fishermen used to collect about 5,000kg of spawns from the river. If carps do not release spawns in the river, it will be an irreparable damage, he pointed out, adding, “We stand to lose the original variety of carps.”
He said he collects data from primary sources like the spawn collectors during spawning in the river and so his data is accurate. According to him the DoF collects data from secondary sources like the traders.
Pravati Debi, deputy director, Fish Inspection and Quality Control, DoF, Chittagong, said carps released spawns in three phases this year on a small scale, adding, around 168kg spawns were collected in 2016.
When asked why this figure was significantly larger than that of the researchers and spawns collectors' accounts, she said the DoF officials collected information from every quay where the spawns are sold.
She, however, admitted that spawning in the river has decreased to a great extent in recent times due to pollution. the DoF has conducted a study to find the reasons and level of pollution in Halda and to learn about other threats.
“Once we get the report, we'll take necessary steps as per recommendations,” she said.
Azadur Rahman, director of the Department of Environment (DoE), Chittagong, said as per environment laws DoE has controlled industrial pollution in Halda to a great extent.
As there is no legal ban preventing tobacco cultivation, the DoE cannot stop it, he said. “If the government takes any decision to ban tobacco cultivation around Halda, we will enforce that law.”
He said the government is pondering to declare Halda an ecologically critical area to protect its unique trait.
Contacted, Dr Md Khalilur Rahman, director (admin and finance), and chief scientific officer of Bangladesh Fisheries Research Institute, said Halda is the only tidal river where carps release spawns.
“It's a unique and valuable wealth of the country,” said Rahman, also director of the Halda Research Project initiated by the Ministry of Fisheries and Livestock, adding, “So the government should take immediate steps to conserve the river.”
“A commission for the river should be formed and Halda should be declared a national river,” he emphasised.
“Water obstruction through the rubber dam must be stopped. A portion of the river turns into a desert due to it for which the mother fish cannot be ready to release spawns,” said Prof Dr Umme Kulsum Navera of the water resources engineering department of Buet.
“Non-functional sluice-gates in the river should be redesigned and all the sluice-gates must be made fish-friendly,” she said.
Navera, also team leader of the research project, said the river must be freed of pollution from industrial and domestic effluents.
Tobacco cultivation around the river should be banned along with operation of the mechanical dredgers, she stressed.
Mohammad Ali, general secretary of the Committee for Saving Halda River, said some brick kilns and poultry farms are also operating around the banks, polluting the river.
He suggested instead of mechanical dredgers, manual ones may be used to extract soils, if necessary.