Cuttlefish Use Electrical Cloaking to Hide From Sharks

The common cuttlefish is capable of electrically cloaking itself to avoid predators. Hans Hillewaert via Wikimedia Commons

Cuttlefish are masters of disguise. These cephalopods can blend into a wide variety of backgrounds to hide themselves from predators, such as large fish and sharks.

Invisibility doesn't always work, though. Sharks and other fish have organs that can detect electrical fields that all living things emit as a normal consequence of metabolism. So cuttlefish have also evolved a shocking way to make themselves less electrically "visible."

A study published today in the journal Proceedings of the Royal Society B found that when cuttlefish (Sepia officinalis) see images of a threatening large fish or shark approaching their tank, they freeze. They not only greatly slow down their breathing but also put their arms over the siphons on either side of their head, which emit bioelectric fields. They also clamp down openings within their mantle (the main part of their body behind their head), which is the other major source of electrical field emissions.

The researchers calculated that these actions reduce the electrical output of the cuttlefish by 89 percent, making them less noticeable to sharks. They also found that the cuttlefish didn't take these actions when an animal approached that wasn't deemed a threat, such as a crab.

In a subsequent experiment, the scientists simulated a cuttlefish with electrodes, emitting the same amount of electricity as the animals do in the presence of bonnethead and blacktip sharks. These sharks bit these electrodes, apparently assuming they might be a tasty treat. But when the electrical fields were reduced, as when the cuttlefish freezes, the sharks were 50 percent less likely to investigate and bite them.