Miyagi Prefecture Aims for Fishermen to Switch to Pearl Cultivation as Catch Volumes of Other Shellfish Drop

By Kazuki Yoshida / Yomiuri Shimbun Staff Writer

13:44 JST, December 5, 2025

Akoya pearl oysters have been found off the coasts of Miyagi and Iwate prefectures since last year. While the northern limit of their habitat on the Pacific side was previously considered to be off the Boso Peninsula in Chiba Prefecture, rising sea temperatures may be influencing the shift. Miyagi Prefecture started surveying the population of pearl oysters in November and is actively pursuing pearl cultivation research with the aim of creating a new income source for fishermen.

Change of northern limit

Last October, Akoya oysters were first discovered for the first time in the sea off Miyagi Prefecture. Local fishermen found them attached to farmed oysters off the coast of Ishinomaki. After the prefectural government requested information, about 200 specimens were brought to the prefecture’s Fisheries Technology Institute from Kesennuma City and Minami-Sanriku Town, among other locations.

According to the prefectural government, Akoya oysters mainly feed on phytoplankton and grow to be able to produce pearls in about two years. Officials of the prefectural government said that if sea water temperature is around 10 C, the environment is not suitable for the growth of the pearl oysters.

According to Shusaku Sugimoto, an associate professor at Tohoku University who studies climate change, due to the effects of the Kuroshio Extension, a branched flow from the Kuroshio warm current, annual average temperatures of waters in the seas off Fukushima, Miyagi and Iwate prefectures have been higher by 6 C since 2023 than an average year until then. He believes Akoya oyster larvae drifted to the sea off Miyagi Prefecture, survived the winter and grew.

Young pearl oysters were also found off Ofunato, Iwate Prefecture, in December 2024.

Miyagi Prefecture is focusing on researching the pearl oysters because there have been poor catches of oysters, scallops and other marine products in recent years. The catch volume of Miyagi Prefecture’s sea squirts, the highest in the nation, has continued to decline, and in fiscal 2024 fell more than 60% from the previous year, while scallops also decreased by more than 40%.

Rising sea temperatures are seen as a contributing factor, and this trend is likely to continue.

Takuya Nitta, who cultivates oysters in Ishinomaki, said his catch volume of the shellfish in fiscal 2024 fell to about one-third from an average year. He said, “It’s nature we’re dealing with, but I’m really frustrated.” Because such poor catches have continued, he said, “I can have a dream in pearl farming.”

Full-fledged study

According to the Agriculture, Forestry and Fisheries Ministry’s statistics, Nagasaki, Ehime and Mie prefectures account for about 90% of production volume of cultured pearls in Japan. While production has fallen from about 125 tons at the peak in 1967 to 12.8 tons in a preliminary 2024 report due to a shortage of workers and other factors, the prices of cultured pearls have been on the rise due to increasing demand from China and other countries.

However, establishing technologies of farming pearl oysters is not an easy task.

In February this year, the Miyagi Prefecture Fisheries Technology Institute conducted an experiment where it returned 49 pearl oysters to the sea to grow, but all died within about two months. It is assumed that they died because water temperatures in early spring temporarily dropped close to the seasonal average at the 6 C level.

To harvest high-quality pearls, it is necessary to move aquaculture rafts for the farming in accordance with the changes in the season and sea water temperature. Mastering the technique of inserting the nucleus, which forms the pearl, into the shell is also essential. Atsushi Takekawa, chief researcher of the institute, said, “Though it is a long-time and difficult challenge, we want to provide fishermen with new options.”

Takeshi Takeuchi, senior researcher at the Mikimoto branch of the Japan Pearl Promotion Society in Shima, Mie Prefecture, offered encouragement. “This research is valuable not only for increasing interest in the pearl industry but also for understanding changes in the ocean.”