Octopus-fish hunting clubs: no despots, some punching

Despite being a solitary creature, the day octopus (Octopus cyanea) has sometimes been spotted hunting with inter-species groups of fish.

Scientists assumed that the octopus is in charge of the hunting pack, but a new study finds that influence is actually shared around, depending on the situation.

But, say the international team of researchers, an octopus might still change the hierarchy by punching a fish.

The study is published in Nature Ecology & Evolution.

The researchers followed octopuses around on diving expeditions in the Red Sea.

They filmed 13 different octopuses in hunting groups, each of which contained several other species of fish.

The hunting groups were looking for prey shared by the octopuses and their fish colleagues, like molluscs and crustaceans.

The team reviewed 120 hours of video footage collected on these missions, looking for examples of social interactions in the groups.

They found that different creatures took the lead on different decisions.

For instance, goatfish were better at exploring the environment and more likely to decide where the group moved next.

Octopuses, meanwhile, held the reins on deciding whether or not to move.

The researchers say in their paper that, contrary to previous beliefs, leadership in these groups “is demonstrably not despotic, but shared”.

But there were still hierarchical struggles within the group. Fish darted at each other in order to displace them, while octopuses would occasionally punch a fish to the outer edge of the group.

Blacktip groupers received the highest proportion of octopus punches.

Inter-species hunting groups generally ate better than individual octopuses or fish, suggesting this arrangement is beneficial for everyone.

The researchers point out in their paper that octopuses diverged from the fish they’re hunting with 550 million years ago, making this a collaboration between extremely different individuals.

While other inter-species hunting groups are known about, in birds and badger-coyotes, this group has more complex social rules attached to it.

“The exhibited range of partner-dependent behavioural flexibility, especially concerning the use of social information when deciding to switch foraging strategies and whom and when to punch, indicates that day octopuses have hallmarks of (heterospecific) social competence and cognition,” write the researchers in their paper.