The experts in the port city underscored the need for taking immediate initiatives like creating awareness among the locals, river training as well as renovation and restoration of the canals and the springs flowing into the Halda to get back the river in its state which was highly congenial for fish spawning.

Indigenous species of giant fishes like Ruhi, Katla, Mrigel and Kaliboush migrating from the river Karnaphuli, the Matamuhuri and the Sangu released fertilised eggs in an astounding number at the spawning centre of Halda during Baishakh and Jaishtha (April and May) every year.

At this time a 10-km stretch of the river from Satterghat to Madunaghat of Raozan upazila took a festive look with hundreds of local people in small boats collecting fertilised eggs.

But netting of mother fishes and bend cutting that shorten length of the river and raise salinity in its water, caused spawning in the Halda to fall at an alarming rate, the experts said.

Spawning at the Halda marked a serious decline with some 9000kgs of spawns collected this year against the average collection of around 65,000kgs in the early fifties, said Mohammad Ali, who has been carrying out a study on the river for more than five years.

Earlier, the Halda provided around 70 percent fries of major carps while the rest 30 per cent came from the Padma, Jamuna and the Brahmaputra. But fries of major carps now provided by the Halda has come down to some 33 per cent, he said.

"Since 1947 four ox-bow shaped bends, the most suitable places for releasing spawns in the river, were cut," regretted Ali while talking to The Daily Star.

The bends were cut to shorten the length of the river at Barighona in 1947, Angkurighona in 1961, Sonarmukh in 1990 and Garduara in 2003, he said.

Muhammad Idris, president of Chittagong Nagorik Udyug, an organisation working on the Halda, said sluice gates were set up at different canals flowing to the Halda to reduce flow of water and depth of the river.

As such, saline water of the Bay of Bengal coming through the Karnaphuli raised salinity in water of the Halda to pose a threat to the spawning centre.

He hailed the government for imposing restriction on fishing in some 30km stretch of the Halda from Karnaphuli-Halda juncture to Satterghat from March 15 to July 15.

But he blamed the government for imposing restriction on fishing in the canals and springs where no spawning took place.

He called for opening the canals for fishing to support the livelihood of local fishermen and removing the sluice gates that hampered fish production at the canals.

Prof Manzoorul Kibria of Zoology department of Chittagong University, emphasised the need for creating awareness among the local people to raise rates of egg-collection, hatching of spawning, survivability and production of fries from spawns as well as protecting the brood fishes.

No policy or plan to protect the spawning centres could be successful unless the locals are involved and provided them with alternative jobs, he said.

He called for declaring the Halda stretching from Halda-Karnaphuli juncture to Mirzapur in Hathazari a sanctuary.

"All the marshlands like Gumanmardan, Fatika Beel on both the sides of the Halda up to Mirzapur also have to be declared sanctuary as well," he said.

"Because, most of the springs and canals falling into the Halda flow through the marshlands and carry all the nutrients required for spawns and fishes," he added.

"Once Halda was famous for Ruhi and Kali Boush that used to go to the marshland to get there eggs matured before returning to the river for releasing eggs," said Manzoorul who had been working on the Halda since 2001.

To stop fishing in the sanctuary for six months he suggested income generating projects in and around Halda for the fishermen and locals.

Four original stretches of the river have been detached following the diversion of course through cutting bends, which are now known as "dying canals,” he said.

Projects should be taken up dividing the dying canals into four blocks for increasing Brood Stock, Brood Banks, raising fingerlings (one to two month-old fries) and matured fishes.

Spawns would be released in the Brood Stock block, 18 to 25-day old fries in the Broad Bank block, fingerlings in the third block while the fourth block might be preserved for developing matured fishes.

From the first, second and third blocks spawns, fries and fingerlings could also be sold out to different hatcheries throughout the country.

Fishes could be netted from the fourth block for sale in the market or for releasing as brood fishes in the Halda, he said.

An organisation could play the role coordinator in the process and share the profit among all the stakeholders, he said.

Prof Manzoorul said if such projects could be implemented the Halda would be flooded with spawns and fishes without brood fishes coming from elsewhere.

It would help the fishermen and egg-collectors involved in the project to protect the Halda and its resources, he said.

At the same time training should be there for collecting eggs and hatching in scientific way, he said.

At present only 20 per cent of the released eggs are collected and only 50 per cent of them are hatched while 90 per cent hatching is possible in scientific method, Prof Manzoourul said.