Photo/Illutration “Kaki Komachi,” a brand of fleshy oyster, in Kure, Hiroshima Prefecture, in November 2024 (Asahi Shimbun file photo)

Unusual marine conditions have devastated farmed oysters in the Seto Inland Sea, prompting industry leaders to request government support to deal with the catastrophe.

“This is truly disaster-level,” Hiroshima Governor Hidehiko Yuzaki said on Nov. 19 after meeting with fisheries minister Norikazu Suzuki, who inspected local oyster farms.

One of Suzuki’s visits was to the Morio Suisan farm in Higashi-Hiroshima.

Morio Suisan started harvesting on Oct. 20 but found that more than 90 percent of oysters were dead. Morio Suisan has been raising these mollusks for three years.

“I’ve been a fisherman for over 20 years, and I’ve never seen anything this bad,” company head Tatsuya Morio, 49, said. “How are we supposed to survive?”

Next year’s crop also faces severe risks, he said.

The most severe damage has occurred in Hiroshima Prefecture, Japan’s top oyster producer. Abnormal levels of dead oysters have also been reported across the Seto Inland Sea in Okayama and Hyogo prefectures.

The Hiroshima oyster production measures council, a group of fisheries cooperatives in the prefecture, had delayed the harvest by three weeks from Oct. 1 due to concerns of stunted growth from the intense summer heat.

Yet the situation proved far worse than expected.

“We will investigate the cause and consider financial support for affected businesses,” said Suzuki, who received a petition requesting aid.

The Hiroshima prefectural government is trying to determine what is killing so many of the bivalves.

An official said the prevailing theory is that “oysters simultaneously exposed to high water temperatures and high salinity environments have suffered physiological disorders.”

ABNORMAL MORTALITY RATES

The average percentage of dead oysters upon landing is 30 to 50 percent in a typical year.

The death rate this year has reached 60 to 90 percent in central and eastern areas of Hiroshima Prefecture, according to information gathered by the fisheries ministry on Nov. 14.

Western areas of the prefecture saw rates at or slightly above the usual levels.

Although information on oyster harvests was still being gathered, Okayama Prefecture reported the percentage of dead oysters was “higher than usual.” 

In Hyogo Prefecture, the death rates were roughly 50 to 80 percent but “varied by area.”

According to the fisheries cooperative of Kasaoka in Okayama Prefecture, four of five operators surveyed reported abnormal oyster losses.

“It’s extremely severe,” a cooperative official said.” The harvest should be under way now, but the oysters are too small, so shipments will be delayed.”

Five other fishing cooperatives in Okayama Prefecture that were surveyed by late October found death rates ranging from 6 percent to 73 percent.

“The mortality rate is higher than usual, which is very concerning,” Okayama Governor Ryuta Ibaragi said at a news conference on Nov. 19.

However, he said mortality rates can be initially high in some cases.

“Many voices are saying we should wait and see,” he said.

ECONOMIC, TOURISM IMPACT LOOMS

The city government of Kure in Hiroshima Prefecture had been offering raw oysters as return gifts for the hometown tax donation program. But it has now suspended orders due to poor oyster growth.

“When a specialty product suffers such a severe blow, it has a serious impact on the local economy and tourism,” a city official said.

According to fisheries ministry data, Hiroshima Prefecture accounts for 63 percent of Japan’s farmed oyster output, followed by Miyagi Prefecture and Okayama Prefecture, both at 10 percent, and Hyogo Prefecture, at 6 percent.

The Seto Inland Sea produces 80 percent of the nation’s oysters.

Other regions like Miyagi, Mie and Fukuoka prefectures have reported normal conditions.

(This article was written by Yoshichika Yamanaka, Hiroki Kitamura and Masayasu Kamiyamasaki.)

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