The coral grouper is an agile hunter, quick to chase and attack prey in the open water.
And when its prey dives into cracks and crevasses within a coral reef, the grouper uses its own version of sign language to get help, a new study says.
The fish enlists the assistance of two other predators, the giant moray eel and the Napoleon wrasse, waiting up to 25 minutes for one to come into sight.
When one does, the grouper points its nose toward the concealed prey and starts to shake its body from side to side. This signal is the equivalent of ringing a dinner bell—food is here!
That’s when the interspecies killing team goes to work. The wrasse is the strongman, smashing into the reef and breaking it apart—forcing its prey to flee or get pulverized.
“[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. “They can break coral.”
“Prey will evacuate holes just to avoid getting smashed together with their hiding place,” added Bshary, who observed the behavior during scuba diving research trips to the Red Sea.
While less destructive, morays are no less deadly. Their slim bodies allow them to squeeze into the crevasse to track the prey within. If the fish manages to escape both both wrasse and moray, then the grouper gets one more shot at a meal. (Also see “Herring Break Wind to Communicate, Study Suggests.”)
“Now, while they’ve learned to cooperate, fish don’t share,” Bshary noted. “Whoever gets the prey, swallows it whole.”
Even with multiple parties competing for one food source, groupers are more successful in a group. (See a picture of a goliath grouper.)
When hunting alone, groupers only catch their prey about 1 out of every 20 attempts, Bshary said. When they have help, the ratio is significantly better—about one out of seven, he added.
Groupers can also use sign language as a call to action. Sometimes before prey has been sighted, groupers will approach a wrasse and moray and shimmy, which translates into a request for a team hunt. The trio will scour the ocean, each utilizing their own unique skill sets. (See pictures of ocean animals’ survival skills.)
“They all go hunting together,” said Bshary, whose study appeared April 23 in Nature Communications. “It looks quite impressive when they come all together and start inspecting.”
Scientists still haven’t figured out why groupers are able to communicate with other species. While people, apes, and some birds are adept at signaling, the scientific community previously thought a fish’s tiny brain wasn’t up to the task.
Bshary and his team have logged a lot of hours underwater to study the grouper’s odd disco, braving pruny fingers and wicked sunburns.
“There’s this idea that you need a large brain to use referential gestures, [but] even a fish with a rather standard brain shows this ability to produce referential gestures,” Bshary said. “This is important. It’s decoupling cognitive abilities from brain size.”
The next step, he said, is to repeat the experiment with the species within the lab to see what other secrets the grouper’s strange signs may unlock.