Roy shares about Electricity Underwater
Written by Roy Kittrell, January 2025.
Many years ago, on a night dive in Tioman Island, I saw a small stubby looking stingray on the seafloor and took a picture without much of an afterthought. Later after I had uploaded it to iNaturalist it was identified as a Finless Sleeper Ray (Temera hardwickii)… a type of electric ray!
The stingray family Torpedinidae (hence why they are also known as ‘torpedo rays’ have evolved the unusual ability to be able to produce electricity from electrocyte cells on their underside. They can emit a surprisingly powerful electric shock to defend themselves against predators and also to stun their prey. The shock for this species is estimated to be around 20 volts; for comparison this is twice as strong as putting your tongue on a rectangular 9-volt battery… definitely enough to make you notice!
What was more interesting to me too was that they are capable of producing this shock even when they are still juveniles, as I saw in this video on YouTube.
While producing electricity is a relatively rare phenomenon in the ocean, electroreception itself is nothing new for Rays and Sharks in the class Chondrichthyes, commonly referred to as cartilaginous fish. Sharks, and especially the hammerheads, are adept at using electroreception to hunt down and eat their prey. In fact, it’s largely why their heads (the cephalofoil) are shaped like hammers, it allows for more precise electroreception by spreading these receptors over a large area.
Muscle movements of prey animals such as fish and crustaceans actually generates an extremely weak electrical current in the water, so weak that these sharks have had to evolve incredibly sensitive organs to be able to detect them. So sensitive in fact that hammerheads can detect electrical fields as weak as 5 billionths of a volt per centimeter (5 nanovolts/cm)! This is so sensitive they can detect muscle movements and even the nervous systems of animals when they’re buried under the sand… absolutely amazing!
Perhaps even more amazingly, it’s been shown that hammerheads also use their magneto-receptors to orient themselves to Earth’s magnetic field, allowing them to navigate and migrate accurately over huge distances across the oceans. I was even lucky enough to see them doing this on my trip to Mikomoto Island in Japan last year.
Next time you see a Shark or a Ray on one of your dives with Flow, I hope you have a newfound appreciation for how amazing these animals are!
Roy Kittrell is an avid naturalist and underwater photographer, his work can be found on instagram @roythedivebro