Sharks Can Sense When A Storm’s A Brewin’.

Hurricane eye.

By Kristy Walsh, science writer and volunteer content contributor for Shark Angels.

Have you ever felt a storm coming? Some people say they can “feel it in their bones.” Other people, like meteorologists, use radar towers, satellites, and supercomputers to build a weather forecast. Well, guess what—sharks can predict the weather too!

That’s amazing! But how do they do that?

The answer lies in the atmosphere. We live at the bottom of a huge ocean of air that surrounds the planet—this is called the atmosphere. While it’s not clear where the upper boundary is (it’s somewhere more than 6,000 miles above us!), we know that most of the Earth’s atmosphere can be found 5–9 miles above the surface.  

Barometric pressure (also called atmospheric pressure) is the weight of Earth’s atmosphere above a particular place. When we’re standing at sea level, for example, there are more air molecules above us, so the barometric pressure is higher. But when we move to higher altitudes—like, say, to the top of a mountain—there are fewer air molecules above us, so the pressure is much lower.

So, what does barometric pressure have to do with storms and sharks?

Hurricanes need two things in order to really get cooking: warm ocean water and wind.

For a hurricane to form, the ocean’s surface (or just the top 165 feet) needs to reach a temperature of at least 80°F. This heat mostly comes from the sun, but the ocean can also absorb heat from other sources such as clouds, water vapor, and greenhouse gases.

Then, the wind comes along to evaporate the water—creating a layer of warm, moist air above the ocean’s surface. Warm air rises (because it isn’t as dense as cooler air) and the moisture condenses to form clouds and rain; this sudden air movement causes the barometric pressure at the ocean’s surface to drop, sometimes rapidly.

Cooler air rushes underneath the rising warm air, bringing more moisture and causing the storm to spin: either to the right (if we’re in the Northern Hemisphere) or the left (if we’re in the Southern Hemisphere). Once wind speeds reach 74 mph, you’ve got yourself a hurricane.

hurricanes affecting waves on shore.
Credit: majicphotos/Shutterstock.com

We all know what hurricanes are like on land. They’re extremely powerful and can be devastating to people, coastal cities, and towns. Well, ask any shark in the ocean, and they’ll tell you, things aren’t any better underwater.

Hurricanes can generate massive waves (as high as 60 feet!) and powerful surges of underwater currents (as deep as 300 feet!), not to mention changes in oxygen levels and salinity (or saltiness) as the ocean’s deep and surface waters mix—all of which can be deadly for marine life. 

In order to stay alive and safe, sharks must be able to read their environment and respond quickly to changing conditions. Any sharks who want to escape the effects of a hurricane need to start swimming well before the storm arrives. But sharks can’t watch the news, so how do they know when it’s time to leave?

Well, remember barometric pressure? There’s a growing body of research that suggests sharks can actually feel changes in barometric pressure—either through their inner ear or something called a lateral line—and this gives them a heads-up that a storm is on the way.

Wait, wait, wait. Sharks have ears?

That’s right! They might not look like much from the outside—two small holes on either side of their heads—but they’re highly sensitive (so you better not tell any secrets around them!). A shark’s inner ear is lined with sensory hair cells, which scientists suspect could allow them to detect the pressure changes associated with an approaching storm.

Those same sensory hair cells are also found in the shark’s lateral line system, making it yet another tool in its storm detection toolbox. Simply put, the lateral line system is a tube of sensory cells used to detect pressure changes in the surrounding waters, like when water is displaced by free-swimming marine life… or when a storm comes rolling in.

Wow, so the ocean is teeming with super-powered, pressure-sensitive sharks that are basically fast-swimming meteorologists, dodging storms like it’s their job?  

Yup. But here’s the thing—not all sharks choose to skedaddle when the weather gets bad. When it comes to hurricanes, whether a shark decides to stick around or swim towards safer waters may depend on the species.

hurricanes affecting sharks underwater.
Image: Dray van Beeck/Shutterstock.com

For example, juvenile blacktip sharks (Carcharhinus limbatus) and juvenile bull sharks (Carcharhinus leucas) were spotted moving towards deeper ocean waters just before Tropical Storm Gabrielle (2001) and Hurricane Irma (2017) made landfall. However, precisely when the sharks tried to leave and whether or not they were successful varied between individual sharks.

Larger sharks sometimes decide to weather the storm—and that’s a gamble that can pay off.

underwater effects of hurricanes on sharks.
Image: kaschibo/Shutterstock

Despite a direct hit from Hurricane Matthew (2016), tiger sharks (Galeocerdo cuvier), which are considered one of the more robust shark species, remained in shallow waters and nearly doubled in numbers shortly after the storm. Tiger sharks aren’t picky eaters, so scientists suspect they were scavenging on dead animals left behind by the storm.

Okay, so all of this is very impressive. But why is it important?

As one of the ocean’s top predators, shark’s play a critical role in preserving marine ecosystems. Not only do sharks keep prey populations in check, but the simple fact that they’re around discourages other species (such as turtles) from overgrazing on important ocean resources like seagrass beds.

You see, ecosystems are intricate and delicate things. The loss of an apex predator has been known to knock entire ecosystems off balance, with far-reaching and devastating effects on things like water quality and essential (but limited) resources. That’s why it’s helpful to understand whether, when, and how sharks respond to violent storms, like hurricanes. Because extreme weather is becoming more common, and likely to get a boost from climate change. Good luck out there, sharks. And if you figure out how to tell who’s going to win the Super Bowl, please let us know!

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