The schools of scallops blanket the seafloor in Rausu, Hokkaido, in June, with some of them leaping to relocate. (Video by Tetsuro Takehana)

Photo/Illutration Scallops congregate along the coast of Rausu, Hokkaido, blanketing the seafloor. (Asahi Shimbun file photo)

RAUSU, Hokkaido--Large groups of scallops have covered the seafloor along the coast of the town here in the eastern Shiretoko Peninsula, creating a breathtaking sight underwater as far as the eye can see.

The scallops began gathering here in early June. They typically disappear when the water temperature drops in autumn.

Measuring around 10 centimeters in diameter, the scallops were blanketing the seafloor without any space in between in mid-June, when underwater filming was conducted. The water temperature was measured at 8 degrees.

A maximum of 59 scallops per square meter were recorded at a depth of around 10 meters, according to previous research conducted by Yasuto Nishino, professor of biological oceanography at the Tokyo University of Agriculture.

“It is estimated that hundreds of thousands of scallops gather in this limited area in Rausu alone,” he said. “The whole reason for the gathering here is still shrouded in mystery, however.”

The topography is considered one of the reasons the scallops congregate in this coastal sea area.

The area has a place where the land stretches out toward the sea, causing tidal currents to collide.

Nishino believes it creates an environment conducive to the gathering of the scallops’ food source, such as phytoplankton.

When many scallops leap from the seafloor, they also stir up nutrients from it. He said this may lead to a “virtuous cycle” that further increases the amount of phytoplankton.

SURPRISINGLY FAST SWIMMERS

While scallops usually stay still on the seafloor, they move swiftly when needed.

Susumu Chiba, a professor of aquaculture at the Tokyo University of Agriculture, said one scallop possesses around 80 eyes, enabling them to detect approaching predators such as starfish.

When they sense such danger, they swim away as if flying.

Scallops use a jet propulsion system in swimming, forcefully expelling water from between their two shells. When they want to move to another location, they propel themselves by repeatedly pushing out small bursts of water.

Off the coast of Rausu, many individuals were seen moving while stirring up the sand on the seafloor.

Smaller scallops tend to swim more actively, and some of them move by repeatedly jetting water.

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