The first time Eduardo Sampaio saw an octopus get up and punch a fish, “I started to laugh,” he said. This was a problem because he was diving in the Red Sea and almost choked on his dive regulator.
While an octopus wrapping one of its arms and dropping it explosively on a fish that comes too close has been seen before, the context was new. The octopus Mr. Sampaio observed hunted to feed alongside other sea creatures, and this was the first time that anyone had seen an octopus hay machine thrown during this behavior.
Mr. Sampaio and his co-authors published their observations of several attacking octopuses in Ecology last week. They hope their research will help to reveal the dynamics between these groups of animals, which can balance their conflicting interests through subtle – and less subtle – negotiations.
Octopuses are known as solitary predators. But sometimes, an octopus participates in an underwater hunt, traveling with fish of various species that are also looking for a meal. The study of this activity is part of the PhD research of Mr. Sampaio at the University of Lisbon in Portugal and at the Max Planck Institute for Animal Behavior in Germany.
Although the animals hunt together, Mr. Sampaio is careful not to call this cooperation. The mechanics of the group are not well understood, but the animals seem to do different jobs. While an octopus investigates cracks in rocks and corals, certain fish can patrol the seabed and others can wait in the water above. Some fish may be just fishermen.
But in other cases, fish can work together more directly with octopuses. The researchers saw groupers and coral trout, when their prey hid in a crack, make a head stop dancing over the place. This head stop appears to signal partners, including morays or octopuses, who then approach and use their flexible bodies to expel prey.
In these hunts, Sampaio said: “It is beneficial for both the fish and the octopus that the partner is present”.
Sometimes, however, the octopus would like a partner to be a little further away. That’s when he punches the stomach.
These punches are not common, says Sampaio. He recorded about eight examples during three months of diving in the Red Sea.
In some cases, there was a clear reason for the aggression. An octopus took a fish out of the way so it could grab prey. Other times, it was not immediately clear what a fish had done to deserve a beating.
Perhaps launching a fish to the periphery of the hunting party will teach you a lesson, how not to steal from the octopus. Another possibility is that the punch is a learned response.
“The simplest explanation here is that octopuses may have negatively associated the loss of prey with the fact that a fish follows them,” said Alexandra Schnell, a comparative psychologist at the University of Cambridge who studies cephalopod intelligence and was not involved in research.
She also said she was not convinced that the octopus and reef fish were working together during these multi-species hunts.
“There is no doubt that this is wonderful footage,” said Schnell, but what is visible to the human eye in the Red Sea videos “is just a piece of the puzzle.”
Mr. Sampaio is doing more analysis of these videos now. As a forensic scientist reconstructing a crime scene, he is building 3-D models of how all animals move within a hunting party. He wants to learn more about the interaction network: who leads and who follows? Where does the octopus look for information? And does a well-placed punch change a fish’s behavior?
Whether a fish understands the message or not, Sampaio says he doesn’t think octopuses punch at random. That’s because animals tend not to play when food is at stake. “Their main motivation is to eat,” he said. “So when that comes into play, the gloves fall off.”