Japan's vital oyster farming industry is facing an unprecedented crisis, with officials reporting mass deaths of shellfish in the nation's primary production zone, a disaster directly linked to warming ocean waters.
Unprecedented Losses in Hiroshima's Heartland
In coastal areas surrounding the Seto Inland Sea in western Japan, a region responsible for more than three-quarters of the country's farmed oyster output, a staggering 90 percent of cultivated oysters have perished. This alarming situation was confirmed by officials on Monday, December 1, 2025.
Tatsuya Morio, an oyster farmer with over two decades of experience, expressed his shock to AFP. "I've never experienced this in my whole career," he stated, highlighting the severity of the event. The crisis is centered in the Hiroshima area, which borders the Seto Inland Sea.
The Climate Change Culprit: Data Points to Heat
Local authorities point squarely at elevated sea temperatures as the primary cause. Shoichi Yokouchi, head of the marine products division in Hiroshima, suspects "high water temperatures, together with other factors, are the culprit of oysters dying en masse."
Prefecture data reveals a stark temperature increase. From July to October 2025—a critical growth period for oysters—the average water temperature along Hiroshima's coast was 1.5 to 1.9 degrees Celsius higher than the 1991-2020 average. Yokouchi explained that sustained warmer conditions weaken the oysters' immune systems, making them far more vulnerable to viruses and bacterial infections.
Further compounding the issue was low rainfall in July, which Shinichiro Toi, an official in charge of marine product technology research, said increased salt concentration in the water, causing additional damage to the shellfish.
Economic Fallout and Regional Disparity
The mortality rate for harvested oysters is typically between 30 and 50 percent. However, a mid-November survey by Japan's Ministry of Agriculture, Forestry and Fisheries (MAFF) found devastating losses of 60 to 90 percent in central-eastern Hiroshima Prefecture.
The impact on surviving oysters is severe. Daiki Takeuchi, a 33-year-old oyster farmer in nearby Hyogo prefecture, told AFP that his surviving stock "had grown poorly," reaching only about half their average size. "It's difficult to sell them, to be honest," he admitted. Even varieties believed to be more heat-resilient have been affected, as noted by farmer Morio.
In a contrasting note, the MAFF reported that oyster beds off the Sanriku coast in northern Japan, which produce roughly 17 percent of the nation's farmed oysters, have so far been spared from the mass die-off.
The MAFF and local governments are jointly investigating the precise cause. This event occurs against a global backdrop where, according to the UN's IPCC, the rate of ocean warming has more than doubled since 1993, with record sea surface temperatures set in 2023 and 2024.
The crisis threatens a valuable export industry, with key importers of Japanese oysters including:
- Hong Kong
- Taiwan
- Singapore
- Vietnam
- Thailand
