China's heatwaves threaten to dry up supply of delicious 'hairy crabs'

The last three years have been the toughest for Xie Dandan and her family during more than a decade cultivating one of China's most esteemed culinary delicacies, the "hairy crab", named for its furry claws.

"From 2022, it feels like the weather has been getting worse every year," said the 34-year-old, standing amid tanks filled with the crabs, coveted for their sweet flesh and golden roe, while she wrapped some in straw to prepare them for customers.

"We've come to mentally prepare for these losses." Xie is among the farmers at Yangcheng lake in the eastern province of Jiangsu being forced to devise new ways to keep the crustaceans alive as unusually high temperatures and longer-than-expected summers have disrupted breeding cycles since 2022.

The Chinese mitten crabs, as they are also known, can sell for hundreds of dollars when exported in sets of four to countries such as Singapore and Japan.

"Those who work in agriculture are at the mercy of the sky," said Xie, whose community reeled last year from losses caused by the strongest typhoon to hit the east coast since 1949, ripping out nets and shutting down oxygenation systems.

Higher temperatures than usual spell a triple threat for the crabs by slowing their growth, reducing the amount of oxygen in the water and boosting growth of bacteria, said Kenneth Leung, a marine environment expert at the City University of Hong Kong.

Hopes for a bumper harvest this year were crushed by summer temperatures around the lake in Suzhou city famed for some of the tastiest crabs, which stayed above 30 degrees C (86 degrees F) until late October, delaying their maturity.

The labour-intensive cultivation of the crabs begins with farmers growing their larvae in ponds for about a year before they are moved to fenced farms within the lake for the creatures to molt, or shed their outer shells, as they grow.

Molting happens about five times between March and the traditional end-September start of the harvest, Xie said.

But stronger heat can kill crabs as they shed their shells, in addition to the delay in maturity caused by longer summers.

In 2022, farmers dumped blocks of ice into the water to cool it, Xie said.

Some of eastern China's hottest and longest summers in the last three years have brought temperatures of 40 degrees C (104 degrees F), or higher, on consecutive days as early as July.

In September, weather officials said this year's summer was China's hottest since 1961, while northern rains were the longest in the same period, bringing disruptions that scientists have linked to climate change.

Leung suggested selective breeding as a possible solution, by choosing crabs with a greater tolerance of higher temperatures for breeding.

Authorities expect the lake to yield a harvest of 10,350 metric tons this year, roughly in line with previous years' figures, except for 9,900 tons last year, when the typhoon hit.

While crab farmers may pray for better weather next year, they know they ultimately have little control, Xie added.

"We only can see whether the hairy crabs will be able to adapt, and if they can't, then maybe this industry will just be eliminated. We can't do anything about it."