Scribal Terror: Partners in Predation

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Why is this moray eel smiling? He has a grouper for a hunting buddy. Eurekalert reports on some fascinating evidence of cooperation between these two very different marine species:

In an article published today in PLoS Biology, Redouan Bshary from the University of Neuchâtel and colleagues describe the astonishing discovery of coordinated hunting between groupers (Plectropomus pessuliferus) and giant moray eels (Gymnothorax javanicus) in the Red Sea. These two species make a perfectly complementary pair. The moray eel can enter crevices in the coral reef, whereas the grouper hunts in open waters around the reef. Prey can escape from the grouper by hiding in a crevice and from the moray eel by leaving the reef, but prey has nowhere to go if hunted by a combination of these two predators. The article offers a description and accompanying videos, such as the one showing a grouper and eel swimming side by side as if they are good friends on a stroll. It also offers quantification, which is truly hard to achieve in the field, of the tendencies involved in this mutually beneficial arrangement. The investigators were able to demonstrate that the two predators seek each other's company, spending more time together than expected by chance. They also found that groupers actively recruit moray eels through a curious head shake made close to the moray eel's head to which the eel responds by leaving its crevice and joining the grouper. Groupers showed such recruitment more often when hungry.

There's a video here, which I can't access from work. The photo of the smiling eel is one Warren took during a visit to Shedd Aquarium.