Groupers
hunt for small fish in open water, but sometimes they will beckon to a
moray eel or a humphead wrasse to go hunting with them. Morays and
wrasses will grab fish out of crevices and places a grouper can't reach
-and if it flushes more of them out, the grouper can catch them. But
what is weird is
how the grouper recruits an eel, as observed by Alexander Vail from the University of Cambridge.
The
groupers always summoned the wrasses and morays with a vigorous shimmy,
but they also used a second, much rarer signal—a headstand, combined
with head-shaking. Vail thinks it was a signal, one that said: “The
prey’s in here, guys!”
When doing their headstands, the groupers
always swam over the location of hidden prey that they had failed to
catch. They only used the move when a moray or wrasse was nearby,
continued to do so until one arrived, and stopped as soon as one did.
Most
morays and all wrasses headed towards the grouper’s location when they
saw the signal, causing the prey to break their cover. (The fact that
the prey didn’t abandon their hiding spots beforehand shows that the
headstand itself isn’t a hunting tactic.) And when the morays ignored
the headstand, the groupers actually swum after their partner and either
performed their “recruitment shimmy” or forcibly tried to push the eels
in the right direction.
The researchers were
impressed, but they caution that such cooperative behavior doesn't
necessarily mean these fish have high intelligence. See videos of the
tag teams in action at
Not Exactly Rocket Science.
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