That whirlpool in Japan. Caused, according to a BBC presenter, by currents of water flowing at different speeds.
I had thought that as authoritative a source as Mythbusters had disproved the notion that a boat could be pulled under by a whirlpool, but the BBC reckoned that without aid from its engine, a boat seen passing over the whirlpool would be sucked down. I think they may have suggested to the sea bed itself.
Would a fishing boat crew have had anything to fear from that whirlpool.