Clever Cuttlefish Muffle Electrical Signals to Hide from Sharks

At first glance, the cuttlefish looks like a pretty easy meal. It’s squishy, stubby, and seemingly defenseless. But the cuttlefish doesn't give up so easily.

Like its cousins the octopus and the squid, the cuttlefish has no external shell, and has therefore been forced to get creative in its defenses. Biologists and material scientists alike are captivated by the cuttlefish’s talent for subterfuge. By compressing, stretching, or relaxing pigment and light-reflecting cells, the cuttlefish can change color and even create patterns on its skin. As if that’s not enough, they’ve become shape-shifters, too. Any cuttlefish with a half-second’s head start can vanish into its surroundings.

But all this razzle-dazzle will only thwart predators who hunt by sight. Those that rely on scent or touch won’t be fooled, nor will those hunters who locate prey via electrosensing. 

It’s more common than you’d think. Every living thing gives off at least some electricity. Some, like the electric eel, carry a significant charge. But most of us just trundle along, emitting a faint electrical aura as we go about our daily business.

Scientists’ list of animals that can sense other animals’ electrical fields is growing all the time, and a lot of those animals are aquatic. At the top of the list are sharks, with electrosensing skills 10,000 times more powerful than those of any other animal.  

And what do sharks like to eat? A lot of things, including—you guessed it—the cuttlefish. Once again, it looks like the cuttlefish doesn’t stand a chance—and once again, looks are deceiving. Researchers recently discovered that cuttlefish can actually muffle their electrical fields, rendering themselves nearly invisible.

This insight comes courtesy of Duke University biologist Christine Bedore, who has made it her business to study electrosensing in sea critters. Bedore found that the electric field given off by the common cuttlefish (Sepia officinalis) is quite weak, about 75,000 times weaker than a single AAA battery. But even a weak field is still recognizable to a hungry shark.

To find out how a cuttlefish responds to the sight of a shark, Bedore set an iPad screen against the wall of a cuttlefish tank. She then played the cuttlefish videos of what looked like the silhouettes of approaching crabs, sharks, and groupers (another cuttlefish predator).

The crab silhouette, which presented no threat, didn’t inspire any changes in the cuttlefish’s behavior. But each time the silhouette of a shark or grouper approached, the cuttlefish in the tank froze. Its breathing slowed, and it seemed to be covering parts of its body with its little arms.

Throughout the experiment, Bedore was tracking the cuttlefish’s electrical output. Watch for yourself:

The cuttlefish’s tactic had a huge effect on the strength of its electrical field. By covering its siphons with its arms, the cuttlefish masked its electrical output by as much as 89 percent.

For the second phase of the study, Bedore and her colleagues offered real sharks access to a simulated cuttlefish in two positions: relaxed and frozen. The “cuttlefish” at rest was not only visible, but it was irresistible; the sharks started biting the equipment. The muted electrical field of a frozen cuttlefish, on the other hand, attracted only half as many shark bites. 

Bedore and her colleagues published their findings in the December 2 issue of the Proceedings of the Royal Society B. 

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Big Questions
Why Do Cats Freak Out After Pooping?
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Cats often exhibit some very peculiar behavior, from getting into deadly combat situations with their own tail to pouncing on unsuspecting humans. Among their most curious habits: running from their litter box like a greyhound after moving their bowels. Are they running from their own fecal matter? Has waste elimination prompted a sense of euphoria?

Experts—if anyone is said to qualify as an expert in post-poop moods—aren’t exactly sure, but they’ve presented a number of entertaining theories. From a biological standpoint, some animal behaviorists suspect that a cat bolting after a deposit might stem from fears that a predator could track them based on the smell of their waste. But researchers are quick to note that they haven’t observed cats run from their BMs in the wild.

Biology also has a little bit to do with another theory, which postulates that cats used to getting their rear ends licked by their mother after defecating as kittens are showing off their independence by sprinting away, their butts having taken on self-cleaning properties in adulthood.

Not convinced? You might find another idea more plausible: Both humans and cats have a vagus nerve running from their brain stem. In both species, the nerve can be stimulated by defecation, leading to a pleasurable sensation and what some have labeled “poo-phoria,” or post-poop elation. In running, the cat may simply be working off excess energy brought on by stimulation of the nerve.

Less interesting is the notion that notoriously hygienic cats may simply want to shake off excess litter or fecal matter by running a 100-meter dash, or that a digestive problem has led to some discomfort they’re attempting to flee from. The fact is, so little research has been done in the field of pooping cat mania that there’s no universally accepted answer. Like so much of what makes cats tick, a definitive motivation will have to remain a mystery.

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Watch a School of Humpback Whales 'Fish' Using Nets Made of Bubbles 

Just like humans, humpback whales catch many fish at once by using nets—but instead of being woven from fibers, their nets are made of bubbles.

Unique to humpbacks, the behavior known as bubble-net feeding was recently captured in a dramatic drone video that was created by GoPro and spotted by Smithsonian. The footage features a school of whales swimming off Maskelyne Island in British Columbia, Canada, in pursuit of food. The whales dive down, and a large circle of bubbles forms on the water's surface. Then, the marine mammals burst into the air, like circus animals jumping through a ring, and appear to swallow their meal.

The video offers a phenomenal aerial view of the feeding whales, but it only captures part of the underwater ritual. It begins with the group's leader, who locates schools of fish and krill and homes in on them. Then, it spirals to the water's surface while expelling air from its blowhole. This action creates the bubble ring, which works like a net to contain the prey.

Another whale emits a loud "trumpeting feeding call," which may stun and frighten the fish into forming tighter schools. Then, the rest of the whales herd the fish upwards and burst forth from the water, their mouths open wide to receive the fruits of their labor.

Watch the intricate—and beautiful—feeding process below:


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