Parallels for cetacean trap feeding and tread-water feeding in the historical record across two millennia

Trap feeding and tread-water feeding are cetacean hunting strategies first recorded in the 2000s in two whale species at opposite sides of the globe. In both behaviors, whales sit motionless at the surface with their mouths open. Fish are attracted into the whale's mouth and are trapped when the jaw is closed. We identify striking parallels with the behavior of a sea creature named hafgufa in Old Norse sources. The hafgufa tradition can be traced back to the aspidochelone, a type of whale frequently described in medieval bestiaries, first appearing in the Physiologus, a 2nd century CE Alexandrian manuscript.