With their stout body, blunt face, and quick bursts of speed, groupers are great open water predators. Feeding on mostly fish, octopus and crustaceans, some hunt by ambushing their prey, while others are more active predators. Groupers mouths and gills can even act like a vacuum to suck up food as it approaches.

For the roving coral grouper, however, dinner can be harder to come by. Because of their coral habitat, their prey often hides inside the reef where the grouper can’t get at them. To get around this, the grouper has been found to recruit a partner in crime in order to get their grub. Read more about the grouper’s extraordinary underwater collaborations.

Photo by Matt Kieffer

The Grouper and the Eel

Moray eels aren’t exactly the most approachable looking fish. With two sets of jaws (they have another set in their throat!) and a body that can reach over 4 meters long, they’re a fierce predator. They usually slither through coral reef when hunting. Their speciality is finding food in nooks and crannies. Most fish (and people) want to avoid this not-so-friendly creature at all costs.

That is, except for the grouper.

While conducting research in the Red Sea, marine biologist Redouan Bshary observed (and videotaped) the grouper and moray eel hunting together. To catch a fish, the grouper circles around the reef as the eel slithers inside it. As fish flee the eel, the grouper is waiting, and vice versa. Their complementary skills make them a rather unstoppable duo.

This act of hunting together is something scientists call “coordinated cooperation”. That simply means the fish purposefully hunt together in order to achieve their own independent goals of getting fed. This behaviour has been observed before in mammals and birds, but never in fish. For a long time scientists thought fish did not have the cognitive ability to do something like this, but this discovery has challenged that hypothesis.

Photo by Chris Wilson

The Grand (Referential) Gesture

What makes this cooperative behaviour even more interesting is how the grouper recruits the eel. When seeking out help, the grouper swims over to the eel and performs a shimmy dance. This shimmy seems to say, “Hey, let’s get some dinner!” Once the grouper leads the eel to the prey, it performs a second gesture, something more like a headstand, above the location where the prey is located.

These acts are referred to as a “referential gestures” and are just like when you point at an item you want on a menu at a restaurant. Alexand Vail, another scientist who worked with Bshary, thinks that this gesture is the most important part of this discovery. The grouper directs the action at a listener to draw its attention to an object, triggers a response, and does so with the sole purpose of sending a signal. Further, if the gesture doesn’t work, the grouper usually tries to push the eel towards the prey.

Both Bshary and Vail are quick to admit this is not a tell tale sign of intelligence. It may just be that this gesture is driven by instinctual need rather than fishy smarts. Either way, the tandem of the grouper and the eel reminds us that both animals, and fish, are often not so different to us humans, especially when it comes to food.

Underwater collaborations: More common than we think

Other cases of underwater collaborations have recently been discovered.

Damselfish are a relatively small fish who live in and around coral reefs. They are highly territorial and defend their mats of algae and nests of eggs aggressively. In fact, they have even been found to attack divers! Parrotfish, surgeonfish, and wrasse are common predators of the damselfish, but when they attack alone, damselfish can usually fend them off. To combat this, parrotfish, surgeonfish, and wrasse have been found to team up in armies of anywhere from 30-300 in order to run the damselfish out of their territory to feast on their algae and eggs.

In a more friendly relationship, false killer whales and bottlenose dolphins have been found to form social-bonds across both time and space. Off the southern coast of New Zealand, researchers have identified pairs of dolphins and whales together for over a span of five years and in locations as far as 650 km apart. These two species have been found to hunt, swim, and just hang out together, meaning they develop friendships much like humans do!

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