Forming a silver blanket along the stretch of the Hakodate beach for about a kilometer (0.6 mile) long, the fish got washed ashore on December 7.
The town authority has cautioned citizens not to eat the fish in a notice posted on its website.
Locals claimed that they have never seen anything like it, with some going as far as collecting the fish for sale or consumption.
Echoing the residents’ views, Takashi Fujioka, a Hakodate Fisheries Research Institute researcher, said that he had heard of similar phenomena before, but it was his first time witnessing something like this
The fish may have been chased by larger fish, become exhausted due to a lack of oxygen while moving in a densely packed school, and were washed up by the waves, he opined.
The fish also may have suddenly entered cold waters during their migration, Fujioka added.
There is also speculation that the discharge of treated radioactive water from the Fukushima nuclear plant could also be the cause.
“We don’t know for sure under what circumstances these fish were washed up, so I do not recommend eating them”, he said.
Expressing concern regarding the marine environment, Fujioka said that the decomposing fish could lower oxygen levels in the water and affect the marine environment.
