Japan’s oyster industry is facing an unprecedented crisis, with mass die-offs reported across key coastal regions, particularly in Hiroshima Prefecture, which produces the majority of the country’s farmed oysters. Experts and local authorities have linked the unusually high mortality rates to rising sea temperatures and broader climate-related changes, raising concerns over the long-term sustainability of the sector.
According to officials and fisheries data, oyster mortality rates have surged to as high as 80–90% in some areas this season, far above the typical range of 30–50%. This sharp increase has been described by farmers as “something out of the ordinary,” with many reporting that even surviving oysters are smaller, weaker, and unsuitable for sale.
The crisis has been most severe in regions surrounding the Seto Inland Sea, a major hub for Japan’s oyster cultivation. Hiroshima alone accounts for nearly two-thirds of national production, making the losses particularly significant for both domestic supply and export markets.
Scientists attribute the die-off primarily to last year’s extreme heatwave, which pushed average sea temperatures along Hiroshima’s coast 1.5°C to 1.9°C above long-term norms. The elevated temperatures, combined with reduced rainfall, have led to lower oxygen levels in the water and disruptions in nutrient availability. These conditions weaken oysters, making them more vulnerable to disease, bacteria, and starvation.
Marine experts explain that prolonged warming prevents proper mixing of ocean layers, reducing oxygen supply near the seabed where oysters grow. At the same time, insufficient rainfall has increased salinity levels, further stressing marine life. The combined impact of these factors has created what researchers describe as a “perfect storm” for oyster mortality.
The economic fallout is already being felt across coastal communities. Fisheries in cities like Kure, which depend heavily on oyster production, are reporting severe financial strain as yields decline and product quality drops. Local businesses linked to food tourism and distribution have also been affected, with some restaurants forced to close earlier than usual due to shortages.
In response, the Japanese government has stepped in with support measures, including low-interest loans and aid programmes aimed at helping aquaculture businesses recover. However, industry experts warn that such interventions may offer only temporary relief if underlying environmental conditions continue to worsen.
Researchers are now urging adaptation strategies, such as relocating oyster rafts to cooler waters or adjusting farming depths to mitigate the effects of rising temperatures. Still, there is growing concern that climate-driven disruptions could become more frequent, threatening the future of oyster farming in Japan.
For many long-time oyster farmers, the crisis has cast doubt on the viability of continuing the trade. With recurring environmental stress and uncertain harvests, the next generation may be reluctant to take over a livelihood increasingly shaped by climate change.
