Fish on the hunt have been observed communicating with other marine life while pursuing prey by using a sort of aquatic sign language. Previously, collaborative hunting was a trait known previously in only humans, apes and ravens, according to new research out of the University of Cambridge.
The study found that grouper and coral trout perform "referential gestures," or pointing signals to indicate the location of hidden prey to cooperative hunting partners including moray eels, octopuses and Napoleon wrasses.
On underwater research dives, the team observed numerous instances where grouper and coral trout "performed upside-down headstands with concurrent head shakes to indicate the presence and location of particular prey to cooperative partners."
The grouper were observed as waiting near a hidden prey for as long as 25 minutes for an eel or wrasse to pass by, where the fish would then gesture toward a spot of coral where food was in hiding.
The Napoleon wrasse can use brute force to smash the reef, forcing the hiding prey to die in the destruction or flee and expose itself to being eaten.
"[Wrasse] have a very powerful jaw, and they can destroy holes that aren't well constructed," said study co-author Redouan Bshary, a behavioral ecologist at the Université de Neuchâtel in Switzerland, according to National Geographic. "They can break coral."
The moray eel can squeeze its way into narrow entries in the coral reefs. When a moray eel did not respond towards the fishes' gesture, the fish were observed trying different tactics to alert the eel to the prey in hiding, which researchers say is key evidence that communication is happening.
"Now, while they've learned to cooperate, fish don't share," Bshary told National Geographic. "Whoever gets the prey, swallows it whole."
Still, the tactic raises the grouper's chance of a successful hunt. Bshary said that the fish will normally catch prey in one out of 20 attempts; when they have help, the odds jump to one in seven.
The find opens the door to the possibility of cooperative hunting behavior and communication being observed in other species as well.
"Our results emphasize the importance of a more general evolutionary view of cognition which predicts that species evolve cognitive solutions according to their ecological needs," the authors said in a press statement.
The study "Referential gestures in fish collaborative hunting", is published in Nature Communications.