Tons of Dead Fish Mysteriously Wash Ashore in Japan

Mystery surrounds the phenomenon of tons of dead fish that were washed up on a beach in northern Japan last week.

Sardines and mackerel were washed ashore in Hakodate on Japan’s northernmost main island of Hokkaido on Thursday morning, creating an unsettling sliver blanket that covered almost a mile of shoreline.

Initially, some linked the deaths to the release of treated radioactive water from the Fukushima nuclear plant in late August. They speculated that the release had wrought havoc on local ecosystems.

Marine biologists have concluded that a lack of oxygen in the water may have killed the fish. The first theory is that the fish were being hunted by predators and were herded into the shallow bay by the village of Toi, where the huge numbers of fish quickly consumed all the available oxygen in the water.

An alternative explanation is that the fish encountered a sudden pocket of significantly colder water on their migration route, which weakened them.

Hokkaido, Japan. A large number of dead fish washed up on the beach by the waves, picked up and sold by local fishermen.😱 pic.twitter.com/0xUruXLoD4

— ShanghaiPanda (@thinking_panda) December 7, 2023

Dead fish herded into shallow waters

The fish began being washed ashore on December 7th. Local officials estimated that around a thousand tons of fish had come ashore but suggested the actual figure might be higher.

“At this time of the year, large schools of sardine and mackerel are migrating south off the coast of Hokkaido, and they are often preyed upon by larger predators, such as dolphins and tuna,” said Kevin Short, a naturalist and professor of cultural anthropology at Tokyo University of Information Studies.

“It seems that a large number of these fish were herded into this shallow, half-moon bay where they…panicked and very quickly used up all the oxygen because they had nowhere to go,” he told This Week in Asia.

Daisuke Imura, an official with the Ministry of the Environment based at the Shiretoko World Heritage Centre in northern Hokkaido, said there had been other similar incidents in the prefecture in recent years, although never on such a large scale.

“I think the general understanding is that they died from a lack of oxygen in the water, and we had an issue like this last year here in Shiretoko,” he said. “They said at the time that water temperatures were unusually low, but the local fishermen did not care and they quickly went out and brought in as many as they could.”

In a similar incident recorded in November, thousands of sardines somehow lost direction and ended up trapped in the harbor of the Greek island of Koufonisia.

Locals rushed to the port with fish nets to get as many as they could. The small fish seemed to have been disorientated and were crashing against the sea wall.

A video published on TikTok shows fish landing on the wall. A local is heard saying: “As you can see we do not do fishing anymore. Fish come to land by themselves.”