Groupers hunt in open water, while moray eels move through crevices in reefs looking for fish prey. International scientists discovered that the two species cooperate to hunt. The grouper finds fish and then indicates, by a shake of the head, where they are to the moray eel. The eel swims to where the fish is and drives them out. Either the moray eel or the grouper may get the fish.
GROUPERS AND MORAY EELS COOPERATE TO HUNT
"Groupers are semi-benthic piscivors, which hunt in open water. In order to avoid predatory groupers, reef fish hide in corals (apart from pelagic prey like fusiliers). Moray eels, in contrast, sneak through crevices in the reef and attempt to corner their prey in holes. Consequently, the best strategy for prey to adopt in order to avoid moray predation is to swim into open water. The hunting strategies of the two predators are therefore complementary, and a coordinated hunt between individuals of the two species confronts prey with a multipredator attack that is difficult to avoid; prey are not safe in open water because of the grouper hunting strategy but cannot hide in crevices because of the moray’s mode of attack."
"Both partners increase their hunting success when they are in association."
GROUPERS INVITE EELS WITH A SHAKE OF THEIR HEAD
"Groupers actively visit moray eels at their resting places and make use of visual signals to engage morays in a joint hunt. This involves shaking the head at high frequency (3–6 shakes per second) directly in front of the moray eel, usually a few centimetres away from the moray’s head."Grouper signalling to a moray eel resting in a cave
"The morays responded to head shaking by leaving their crevices, and the two fish then swam off through the reef. Moray eels were never observed to signal to groupers."Grouper and Moray Eel swimming off together after the grouper signalled
GROUPER HEADSTANDS AND SHAKES HEAD WHEN FISH FOUND
THE PAIR COOPERATE FOR THREE-QUARTERS OF AN HOUR
"The joint activity of the two fish, measured from the moment the moray left the crevice until the moray re-entered a crevice and did not re-emerge, ranged from a few seconds up to 44 min."
"Groupers did not always signal to morays when they visited them; groupers could simply pass nearby and/or lay down on the sand next to a moray."
"In addition to signalling before any hunting events, groupers also recruited moray eels after unsuccessful hunts."
"The groupers swam to a giant moray eel that was within 15 m of the prey’s hiding place, signalled to the moray, and apparently tried to guide it to the prey’s location."