DHAKA, Bangladesh — This time of year, Mohammad Shamsuddin normally earns about $120 a month working with the crew of a fishing boat off the coast of Bangladesh.
But on Monday, the central government imposed a 65-day national ban on coastal fishing — the most restrictive ever in Bangladesh, a poor and densely populated country where fish play a central role in the economy and diet.
Mr. Shamsuddin, 30, promptly reduced by about a third the amount of food that he buys for himself, his wife and their three children.
“But I won’t be able to run my family for the next two months with this little amount of savings,” he said by telephone from Bhola District, about a 155-mile drive south from the capital, Dhaka. “And when the savings run dry, my life will be a nightmare.”
Officials say the ban, imposed during the Muslim holy month of Ramadan, will be an annual one to help conserve fish and shrimp stocks over the long term. But fishermen across the nation are girding for hardship, and planning protests in Dhaka, if officials do not offer them compensation.
“This is a nightmare situation for a huge number of fishermen and their family members” because prices typically rise in Bangladesh during Ramadan, said Mokter Ahmed, a spokesman for the National Fishermen’s Association in Cox’s Bazar, a port city with about 200,000 fishermen.
He added that if the authorities cannot prevent illegal fishing off the Bangladeshi coast by fleets from other Asian countries, “the ultimate goal of this ban will not be achieved, and only our fishermen will suffer.”
Tensions over the 65-day ban highlight how governments are struggling to balance a need for long-term conservation with those of coastal communities that depend on fish for short-term survival. Fish stocks worldwide have been declining in recent years because of overfishing and ocean warming caused by climate change.
The tensions are particularly acute in Asia, which has seen some of the steepest declines in fisheries productivity as human populations that rely on fish as a vital protein source have grown.
And Bangladesh, a country slightly larger than New York State that has more than 160 million people, about a third of whom suffer from food insecurity, is a case in point.
The country produced nearly four million metric tons of fish in 2016, a more than fourfold increase from 1990, according to World Bank data. That was only a fraction of China’s huge output, but more than Norway’s and South Korea’s, and nearly as much as Japan’s.
But depletion of fish stocks in Bangladesh, along with pollution, unchecked coastal development and other problems, has led to clear losses of biodiversity and prompted “an immediate need for transformation in coastal and marine governance,” two Bangladeshi scientists wrote in an academic study last year.
As evidence of a fisheries crisis mounts in Bangladesh, the government has said it plans to permanently turn at least 10 percent of coastal and marine areas into protected zones by 2020. It has rolled out a series of weekslong fishing bans in some regions or for certain types of fish, including hilsa, a staple of South Asian fisheries.
A similar 65-day marine fishing ban along Bangladesh’s roughly 400-mile coastline came into effect in 2015, and only applied to commercial fleets. But the current ban, to be enforced by the Navy and Coast Guard, applies to fishing boats of any size.
“These resources will deplete one day if we do not use them sustainably,” Ashraf Ali Khan Khasru, the minister of fisheries and livestock, told the Dhaka Tribune newspaper last week, referring to marine resources in the Bay of Bengal. “We should let fish grow and breed. Otherwise, we will have to suffer in the future.”
Temporary fisheries closures can help manage depleted fish stocks when combined with “appropriate enforcement and alternate opportunities” for those who fish them, said Simon Nicol, a senior fisheries officer at the United Nations food agency’s Asia headquarters in Bangkok.
“Rebuilt stocks provide a greater certainty of catch for fishers,” Mr. Nicol added.
But in Bangladesh, where more than one in 10 people work in the fisheries sector, officials have not announced any plans to compensate fishermen affected by the 65-day ban. Fisheries officials in Dhaka did not respond to requests for comment.
Shah Alam Mollik, a representative of the Bangladesh Fishing Boat Owners Association, estimated that the ban had already plunged about 2.5 million people, including fishermen and their families, into crisis.
Mr. Ahmed of the fishermen’s association said that many small-scale fishermen, who are essentially day laborers, would soon need to borrow money or face starvation if no compensation materializes. He added that fish supplies in Cox’s Bazar were already dwindling, and that people whose diet revolves around fish will suffer even more once prices “touch the sky.”
But the ban could help restore depleted fish stocks in the Bay of Bengal, said Mohammad Mahmudul Islam, a fisheries professor at Sylhet Agricultural University in the country’s northeast, who was the co-writer of the recent academic study on Bangladeshi fisheries.
Many small-scale fishermen in coastal Bangladesh are vulnerable because they are indebted to loan sharks for investment capital, he added, and their ability to fish is often interrupted by cyclones and tropical storms. He said it was crucial that the government provide immediate compensation.
Officials typically offer fishermen 44 pounds of rice per household during a 22-day annual ban on hilsa fishing that takes effect every October. But Mr. Islam said that the ration is insufficient, and that the rice typically only reaches about half of eligible recipients.
Last October, many fishermen across Bangladesh blatantly flouted the hilsa fishing ban. One fisheries officer told the Dhaka Tribune at the time that 50 police sweeps in his district had turned up more than 2,500 pounds of fish and 400,000 feet of netting.
Mr. Shamsuddin, the fisherman in Bhola District, said he would not be fishing anytime soon because the boats he works on have been grounded.
He said that extremely poor fishermen like himself usually subsist on rice, lentils and vegetables.“Now they will have to survive by eating rice only with salt,” he said.