Massive Fish Die-Off in Northern Japan

Residents warned against consuming thousands of tons of sardines and mackerel washed ashore in Hakodate, cause of death remains unknown.

Thousands of tons of dead sardines and some mackerel have washed up on a beach in Hakodate, on Japan's northernmost main island of Hokkaido.
Local residents have been urged not to consume the fish due to uncertainty about the cause of the mass death.
The phenomenon may have been caused by the fish being chased by larger fish, becoming exhausted due to a lack of oxygen while moving in a densely packed school, or suddenly entering cold waters during their migration.
The decomposing fish could lower oxygen levels in the water and affect the marine environment.
This is the first time such an event has been witnessed in the area, despite similar phenomena being reported elsewhere.