When an Eel Takes a Bite, Then an Octopus Might Lose an Arm but Take an Eye

The conger eel was the favorite, weighing at least three times more than its eight-armed opponent. But by the time the video footage begins, the underdog octopus had already asserted its toughness, blocking off the eel’s eyes and stuffing arms into its mouth and out the gill hole.

“I thought that with such difference in size it would be hard for the octopus to avoid death,” said Jorge Hernández-Urcera, a marine ecologist at the Institute of Marine Research of the Spanish National Research Council.

The common octopus not only defended itself, but also seemed to come out on top. The divers who made the video — not scientists — broke up the brawl, and the two animals survived, the octopus tearing off in a cloud of ink.

“It was very impressive to see,” said Dr. Hernández-Urcera, who collects amateur diving videos and analyzes them for previously undescribed behavior. He believed this video, recorded in 2008 off the coast of Galicia in northwestern Spain, showed “the intelligence of octopus and the big repertoire of defensive behavior.” But it was only a single video, not enough to suggest that this eight-armed technique was a regular form of octopus martial arts.

More recently, Dr. Hernández-Urcera acquired additional video footage. Enough, he believes, to show that octopuses will choke, blind and sacrifice limbs in an effort to defend themselves from much bigger eel foes. He published his research in March in the journal Ecology and Evolution.