Fishermen on the Padma and Meghna Rivers in Chandpur say this season’s hilsa run, more than a month after the government lifted its 22-day fishing ban, is leaving them with mostly small fish.

The scarcity of large hilsa in a region that depends on the species for income, food security, and exports has sharpened warnings from scientists who say rising temperatures, pollution, and relentless Jatka (juvenile) fishing are taking a toll on Bangladesh’s most iconic fish.

The 22-day fishing ban was imposed nationwide on October 4 to protect egg-bearing hilsa during peak spawning. The ban ended at midnight on October 26. Fishermen expected plentiful, full-grown fish once the rivers reopened, but they now report that large hilsa have all but disappeared. Most of what they catch, they say, are small-sized ones.

Scientists who study the species say warming rivers are driving biological changes that stunt growth. They note that hilsa still mature but now reach adulthood at smaller sizes.

A visit to Chandpur’s main fish landing center revealed piles of 200- to 500-gram fish, which traders said has become the standard catch. With few large fish entering the market, prices have climbed.

Fisherman Mobarak Hossain said big hilsa barely reach Chandpur anymore. “Fishermen in the south take the big fish before they migrate upriver,” he said, adding that climate shifts are shrinking the fish as well.

Mohammad Yusuf, joint general secretary of the Chandpur Fish Traders’ Association, said the mix has changed sharply. “Half our catch used to be small fish and half large,” he said. “Now only about 10 percent are big. Out of 100 maunds (1 maund is approximately 37.32 kilogram), we’re lucky to get 10.”

Abu Kawser Didar, a scientific officer at the Chandpur Fisheries Research Institute, said temperature spikes push hilsa to mature earlier at smaller sizes. Pollution and shifting river flows, he said, further stress the species.

Researchers classify hilsa between 10 and 25 centimeters as jatka, the juveniles that should grow into adults. But illegal “current nets” with fine mesh sweep up nearly everything, depleting the young fish needed to replenish stocks. Lower river levels intensify the strain.

“Tomorrow’s big hilsa come from today’s jatka,” said hilsa researcher Dr. Anisur Rahman. “We aren’t giving the small fish the chance to grow. Enforcing conservation laws is essential. The species is being pushed off balance. That’s mainly because of climate change, pollution, oxygen loss, shifting channels, and jatka harvesting.”