Japan's Inland Sea Oyster Farmers Reporting Mortality Rates Of Up To 90%; Heat, Oxygen Deprivation Wiping Out Shellfish

The Kure oyster festival is doing a brisk trade in beer and grilled meat on sticks. But the longest queues are in front of the oyster stalls, where chefs shuffle piles of mottled shellfish across griddles, waiting for their hinges to ease and reveal their fleshy interiors. Nobuyuki Miyaoka, who is attending the festival with his son, daughter-in-law and their young children, likes his oysters steamed with sake and served with a few drops of tangy ponzu sauce. “The local oysters were fine until this year,” he says. “They used to be a lot bigger … look how small they are.”

It is not only the oysters’ modest size that worries businesses and consumers in Kure and other locations in the coastal Hiroshima prefecture. For an event held to promote consumption of the area’s most acclaimed contribution to Japanese cuisine, the shellfish are noticeably scarce this year. The region’s oysters – a popular Japanese dish and the lifeblood of fisheries in Hiroshima – are dying en masse, with experts blaming a combination of rising sea temperatures and, last year, a brutally hot summer that deprived the delicate bivalves of oxygen and food. Amid warnings that mass die-offs could become more common, Japan’s government has had to step in to support struggling fisheries that say their livelihoods are being threatened.

Taketoshi Niina looks out at the oyster beds near his fishery in Kure and pronounces this season’s harvest a “disaster”.Niina, who runs a small fishery in Hiroshima prefecture, says about 80% of his oysters are dead when they are brought to the surface. “This is something out of the ordinary. And a lot of those that do survive are in poor condition … they are not of a high enough quality to sell to shops and restaurants.

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In a typical year, between 30% and 50% of oysters die, but the rate this season has reached as high as 90% in parts of Hiroshima, according to the fisheries ministry. “I’ve never experienced this in my whole career,” says Tatsuya Morio, who has farmed oysters in Hiroshima for more than 20 years. Last year Japan suffered an intense heatwave, when the average summer temperature was 2.36C higher than normal, making it the hottest summer since records were first kept in 1898.“ If higher temperatures remain for a few weeks, that weakens oysters and makes them more susceptible to viruses and bacteria,” says Shoichi Yokouchi, the head of the marine products division at the Hiroshima prefectural government.

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https://www.theguardian.com/environment/2026/mar/31/japan-oysters-dying-death-rate-warming-seas-hiroshima