A day of fun fishing for goatfish and octopus
Eduardo Sampaio and Simon Gingins
Octopuses are more sophisticated than we thought: Though they’re generally solitary animals, they can cooperate with fish to hunt for prey and recognize which team members are not helping.
That’s the conclusion of a study on “hunting packs” made up of an octopus and several different fish: the fish would seek out potential prey and call the octopus to it, chasing it away through crevices the fish couldn’t reach.
What’s more, rather than actively helping the octopuses find prey, the octopuses will punch away fish that just wander around the school trying to catch something. “The octopuses understand that the fish are exploiting them,” says Eduardo Sampaio of the Max Planck Institute for Animal Behavior in Germany.
Daytime Octopus (Octopus cyaneaThe hawk-eared …
Sampaio said hunting groups consisting of an octopus and several fish, usually a mix of different species, were first described in the 1990s, but until then it was assumed that the fish simply chased the octopus, trying to catch any prey that escaped its grasp.
During 120 hours of diving in the Red Sea, Sampaio set up two cameras to record 13 group hunts, and his team then manually recorded the three-dimensional movements of each recorded group member for statistical analysis.
“Not only are the fish chasing the octopus, but the octopus is definitely chasing the fish,” Sampaio says. “If the fish are moving quickly and in a straight line in one place, that’s a strong signal to everyone in the school that there’s something interesting there.”
If the octopus ignores the movement, the fish will swim back and forth. “The fish will go back and forth between the octopus and this spot, trying to get its attention,” Sampaio says.
Octopuses’ behavior also differs in groups. When diurnal octopuses are hunting alone, they make many short web strokes in rapid succession. When they’re with fish, they web less frequently but for longer periods of time, sometimes lasting more than a minute. Another study by the team found that the web strokes last longer when the octopuses have caught something.
The researchers found six fish species to be the most abundant in the hunting populations, including the red mullet (Palpeneus Cyclostomus) was the octopus’s best hunting partner, actively searching for prey and guiding it.Epinephelus fasciatus) were least likely to find prey.
The octopus appears to know this: While it punched the dwarf rainbow wrasse just three times, it punched the blacktip reef shark 27 times. “There needs to be at least some species-level recognition that says, ‘This species is good to hunt,'” Sampaio says.
It’s unclear whether octopuses can remember fish that have previously been useful or exploited them — a tricky thing to study, Sampaio said, because it’s virtually impossible to tell individual octopuses apart without a tell-tale characteristic, like a lack of tentacles.
“My point is, octopuses are territorial; some of these fish are territorial, so these interactions are likely occurring between the same individuals over long periods of time,” he says.
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