How sharks avoid the wrath of an extreme hurricane

Hurricane Idalia pummeled Florida on Wednesday morning as it made landfall as a powerful Category 3 storm. Idalia, now a tropical storm off the coast of South Carolina, flooded homes and highways, downed power lines, blew out windows, and has so far been linked to at least one traffic-related fatality in Florida.

Humans have a number of strategies to withstand the impacts of major storms. We fortify our homes, ready flashlights and generators, and, if necessary, evacuate to higher ground. Yet we remain highly vulnerable to storm impacts, as Idalia, Ian, and other recent storms have demonstrated.

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Marine animals, meanwhile, have strategies of their own.

Consider sharks. A handful of scientific studies, dating back at least two decades, suggests that sharks can detect a hurricane like Idalia hours and possibly days before it arrives, rivaling human storm forecasting. Some sharks flee. Others stay put. Both approaches help these predators survive.

Scientists study how sharks and other marine animals respond to hurricanes not just out of curiosity but because many shark species are threatened with extinction — and climate change is intensifying storms. A key question is whether that puts their survival at risk.

Sharks have built-in storm sensors

Scientists use a wide range of instruments to measure hurricanes — satellites, radar, thermometers, and so on. Sharks have meteorological tools, too. When a storm is approaching, atmospheric pressure (i.e., barometric pressure) drops, and that, in turn, causes hydrostatic pressure (i.e., water pressure) to drop, too. Hair cells in a shark’s inner ear can detect these changes, even if they’re subtle. Sharks basically have a built-in barometer.

Research suggests that sharks can detect a hurricane many hours and perhaps even days before it arrives, using these pressure-sensitive cells, possibly along with other, poorly understood cues, such as a change in currents or salinity that might accompany a storm.

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After sensing a drop in barometric pressure, smaller sharks, and those that are young, tend to flee to deeper waters, according to Bradley Strickland, a marine biologist at the Virginia Institute of Marine Science. In 2017, Strickland was tracking the movement of 14 juvenile bull sharks in south Florida when Hurricane Irma struck the state as a powerful Category 4 storm. Nearly all of those sharks, he found, left their homes — shallow waters in the coastal Everglades — before the worst hurricane impacts.

“We saw these juvenile sharks that have never experienced a storm of great magnitude in their lifetimes detect the storm coming and leave in advance,” Strickland told Vox. “What they did was head to deeper water, which was indeed the safest place to be.”

A study published in 2003, meanwhile, documented a similar response but among 13 young black-tipped reef sharks living in a bay south of Tampa. Just before Tropical Storm Gabrielle struck the coast, with near-hurricane-strength winds, all of the sharks left their shallow waters. (They returned to the bay between five and 13 days after the storm.)

Not all sharks, however, evacuate before a hurricane hits. Some larger animals employ a different strategy, perhaps using big storms to their benefit.

Some sharks take advantage of storms to hunt

Strong winds and storm surges could pose a threat to smaller fish during a hurricane. Some large sharks, however, are apparently just fine sticking around. In a recent study, researchers tracked four shark species including tiger sharks and hammerheads in Florida and the Bahamas before, during, and after two hurricanes.

While some of the animals fled ahead of a storm, larger-bodied tiger sharks living in shallow waters in the Bahamas stayed put as their home took a direct hit from Hurricane Matthew, then a Category 5 storm.

“I was amazed to see that big tiger sharks didn’t evacuate even as the eye of the hurricane was bearing down on them,” Neil Hammerschlag, a study co-author, said in a press release. “It was as if they didn’t even flinch.”

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Not only that, but the number of tiger sharks in the area temporarily increased after the storm, said Hammerschlag, a shark researcher at the University of Miami. He suspects that the animals who stayed were taking advantage of all the smaller fish and birds that were killed or weakened by the hurricane. In other words, storms might mean food for big sharks.

In some ways, Strickland says, studies like this reveal that sharks face a similar decision to humans before a major storm: stay or go. “That’s a powerful analogy, and really emphasizes how incredible and significant these natural disturbances are — on our lives and on the lives of sharks.”

Scientists still know relatively little about how extreme storms impact sharks, and what that means as the world warms. But ultimately, hurricanes may not be a big deal for these animals, especially compared to some of the other consequences of climate change, such as the loss of coral reefs. And there may even be a silver lining to our most destructive storms: They present an opportunity to study how animals cope with rapid changes.