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Sharks pretty much turn into werewolves under a full Moon

Sharks are much more likely to come after you when the Moon is ominously full.

By Elizabeth Rayne
Liz Great White Shark GETTY

Maybe Sharknado will never actually happen, but sharks morphing into werewolves? Sort of.

They might not grow fur and claws or howl into the night sky, but sharks are much more likely to come after you when the Moon is ominously full. But why is higher lunar illumination making them bite when most shark attacks happen during the daytime? The gravitational pull that affects the tides is thought to be what is really behind the feeding frenzy, and there could be something about the Moon getting brighter that affects them in unknown ways.

Werewolf myths emerged from the strange behavior exhibited by many animals during a full Moon. Anything that lives in the ocean is inevitably going to be affected by the tides, and sharks are no exception, since the Moon’s gravitational field is strong enough to have effects on Earth. Researcher Stephen Midway of the Florida Museum of Natural History coauthored a study, recently published in Frontiers in Marine Science, that sheds some (moon)light on this.

“We do know that the Moon influences the oceans — whether through forces on tides or the Earth’s geomagnetic field,” he said. “Sharks — like many marine organisms — will respond to their environment, so the chance for a lunar influence on sharks is there, but more research is needed.”

Lunar forces having power over the tides is anything but supernatural. Ocean levels rise and fall because the lunar gravitational field pulls at us and creates bulges as it orbits Earth. Because land also bulges, that may at least partly explain your dog acting weird just short of transforming into a werewolf. Ocean bulges are more obvious since oceans are liquid. Not only do high tides happen on the side of Earth directly facing the Moon, but also at the same time on the opposite side, since Earth’s inertia on that side is greater than the Moon’s gravity.

There haven’t been many studies on lunar-fueled shark attacks. Midway and his team looked through 50 years of data on shark attacks from all over the world and found that they are more likely to get vicious when lunar illumination is over 50%. Sharks can be triggered by lunar phases, which doesn’t necessarily mean a full Moon, either. The species most likely to bite humans are usually apex predators (no surprise there) like the infamous Great White in Jaws. If you hit the beach around a certain lunar phase, depending on where you are, it could potentially become a danger zone.

“Different environments and conditions are more suitable for different shark species (although some occur in both), which is why different communities of sharks can be found along different coasts, such as Florida and California,” said Midway.

It is possible that these swimming rows of teeth can have a greater advantage at snapping up prey when tides are stronger and may influence the behavior of what they eat. They could also be in extra-predatory mode when they know an easy meal is around. Lunar illumination also has some sort of influence, making it easier for sharks to see the silhouettes of their prey at night. Moonlight can’t explain daytime attacks on humans. While we are not supposed to be shark bait, since they don’t crave us much, they might still be hungry and mistake us for prey.

Moon phases usually cause behaviors that are specific to a certain species, but not really in sharks. There was one lunar change that affected only — what else? — Great Whites. Attacks by the successors of Bruce are most common in Australia, South Africa, and the west coast of the U.S. If moonlight really does make sharks sink their teeth into something they shouldn’t (meaning humans), it could be because they see a silhouette moving in the water that may register as an animal they actually like to feast on. They don’t just lunge if they smell blood.

“Because many sharks are similar to each other (when compared to other fishes), it is plausible that many or all sharks could have common responses to Moon effects,” Midway said in the study.

Maybe a movie taking this phenomenon into the realm of science fiction should be a thing. Of course, it would have to be called Sharkwolf.

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