Three oarfish have been found on beaches or caught in fishing nets over the past week, bringing the total discovered this season to seven.
Legend has it that they beach themselves before underwater earthquakes or tsunamis.
Known in Japan as a “messenger from the sea god’s palace”, oarfish are thought to live around a kilometre underwater and surface when sick or dying.
At least 10 were beached in Japan in 2010, months before the March 2011 earthquake that triggered a giant tsunami that killed almost 19,000 people and wrecked the Fukushima nuclear plant.
Social-media users in Japan have claimed the new sightings portend disaster.
“This is no doubt evidence of a precursor to an earthquake. And if it is in the Nankai Trough [an area susceptible to tectonic plate movements], it might be a huge quake,” one Twitter user wrote.
But paleontologist Jason Loxton tweeted: “Oarfish are super-cool, but they don’t predict earthquakes.”
Oarfish sightings in Japan, which is worrisome pic.twitter.com/o1EJyRYVdk— Chris Fafalios (@chrisfafalios)February 2, 2019
And Uozu Aquarium keeper Kazusa Saiba told CNN: “There is no scientific evidence at all for the theory that oarfish appear around big quakes.
“But we cannot 100 per cent deny the possibility.
“It could be that global warming might have an impact on the appearance of oarfish or a reason we’re just not aware of.”
Mr Saiba said that although he doubted the theory’s validity, one possible explanation could be that subtle changes in the Earth’s crust at the bottom of the sea before an earthquake “might cause the current to stir and push creatures at the bottom to the surface”.