Thousands of dead fish mysteriously wash up on beach in Japan

 The fish, mostly made up of sardines and some mackerel, washed ashore in Hakodate on the northernmost main island of Hokkaido on Thursday, covering a stretch of beach about half a mile long.

Local residents said they have never seen anything like it and have been urged not to consume the fish.

The cause of the incident remains unknown, but Takashi Fujioka, a Hakodate Fisheries Research Institute researcher, suggested the animals may have become exhausted while being chased by larger fish.

He said a lack of oxygen while moving in a densely packed group could have led to them washing up on the shore.

The incident coincides with sardine migration southwards, Mr Fujioka said, adding that the fish may have suddenly entered cold waters.

He said he has heard of similar phenomena before, but had never seen it in real life.

Te decomposing fish could lower oxygen levels in the water and affect the marine environment, he said.

The day after the wash-up, city officials were seen inspecting the site and trying to collect the fish, while residents collected them to sell or eat, despite warnings not to.