Electric rays keep sharks at bay by delivering an electric charge – and it seems to be working.
The ocean can be a dangerous place so many marine animals have clever self-defence strategies up their sleeve, including venomous spines and camouflage to stay hidden. But these methods aren’t always effective against large predators like sharks. So, electric rays have another shocking tactic.
According to a new study published in Ethology, scientists from Florida International University Institute of Environment have discovered that electric rays don’t just produce an electric charge to stun their prey. They also use these bolts for self-defence.
The researchers had noticed that there was something special about the rays they saw in Guadalupe Island, Mexico. “They are very bold,” says researcher Yannis Papastamatiou. "Our cameras on white sharks showed these rays up in the water column, one of the most dangerous places to be. They must be pretty confident.”
They soon discovered the reason why. After attaching special tracking tags on white sharks, one of the trackers provided some particularly interesting data. At around 50 metres deep, the shark swam towards an electric ray before suddenly fleeing and rocketing up to 30 metres. A couple of minutes later, the shark swam back down but, this time, swam past without approaching the ray.
They even captured the moment a Gulf torpedo ray in Fuvahmulah, Maldives, zapped a tiger shark that tried to sneak up on it from behind (see footage above). The ray had been buried in the sand when the shark approached – and the predator was still a few inches away when it was blasted by the ray’s electric organ discharge (EOD).
"The shark rolled its nictitating membrane – also known as the third eyelid for shielding the eye from debris, dust and injury – and quickly retreated up into the water column,” says FIU in a statement.
Scuba diving instructor Ali Ansaar shared the striking footage on Instagram.
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To try to find out more, the researchers measured whether there were any differences between shocks that Pacific electric rays (Tetronarce californica) used for predation compared to those they used to protect themselves.
There wasn’t a difference between the maximum voltage but “rays emit longer and more EODs during predatory attempts than they do for defensive purposes,” the study says.
This might be because the rays need to be prepared to lock and load a second time if the shark tries to attack again. “Short duration discharges allow the electric organ to be rapidly reused if a predator returns,” says the study.
But these zaps seem to be enough to keep the rays away from hungry sharks, according to the study: "Our observations, the lack of electric rays in the diets of large sharks, and the bold behaviour of these rays in the wild suggest that EODs may be a highly effective defensive strategy,” it says.
Image and video credit: Ali Ansaar / Florida International University
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