With the Atlantic hurricane season in it peak, one of the questions we have been running across frequently is “what do sharks do during a catastrophic weather event.”

To find out, we reached out to Bradley Strickland, a doctoral student at Florida International University in Miami. One of Strickland’s area’s of research includes a long-term monitoring project within the National Science Foundation’s Long Term Ecological Research program studying juvenile bull sharks. As part of that ongoing study, Strickland has been looking at what happens when a potentially habitat-altering storm pulls through.

And, yes, we asked about Sharknados. To learn more about Bradley’s research, click here.

Can you sum up your research for non-academics and what you were specifically looking at?

We really don’t know a lot about how animals predict and respond to hurricanes. By using small tags that send acoustic pings to listening devices positioned underwater in the Florida Everglades, we studied how juvenile bull sharks responded to Hurricane Irma in 2017.

What kinds of behavioral changes did you see in the sharks when a hurricane or tropical system approached?

Storms can cause animals to do many different things such as frogs increasing their calls and birds eating more before bad weather. One common behavior shared by many animals including sharks, lobster, snook, striped bass, and sea kraits is to evacuate the area if they know a storm is headed their way. Obviously, humans do the same thing when hurricanes come. Mother bull sharks use the Everglades as a nursery where their pups live until they grow large enough to face life in the ocean. Living in the estuary for these critical four years or so gives them plenty of food and limits interactions with many of their predators like larger sharks that live in the ocean. In our study, just before Hurricane Irma approached, almost all of our sharks left the estuary and headed into the open ocean. This is not something they usually do until they are older and big enough to leave the nursery. So it’s interesting to us that the sharks left the familiarity and protection from predators offered by the estuary in order to avoid the dangerous hurricane.

What caused them to act that way?

Hurricanes can cause lots of environmental changes before they make landfall including high winds, storm surge, and high rainfall. Animals can definitely sense these changes, but they may come too late to respond effectively. Tropical storms and cyclones also create areas of really low barometric pressure. We know that many animals including bats, birds, and sharks can detect these drops in barometric pressure. Sharks, for instance, have a very sensitive inner ear, which allows them to detect the pressure changes associated with storms. Our tagged juvenile sharks sensed the dropping barometric pressure from the hurricane hours in advance. We found that they considered both how low the pressure got and how fast the pressure dropped in order to know that conditions were about to be become dangerous.

Why did some sharks react to these changes and some did not?

Our youngest sharks tried to leave the estuary too late and, unfortunately, perished. We don’t really know why these animals didn’t leave the estuary in time like the other sharks. Since they were younger, it could be that they were more hesitant to move into deeper waters that contained scary predators and unfamiliar food. However, what is so neat about this study is that almost all of our sharks exhibited the same evacuation behavior and left within 24 hours of the storm. And most of these tagged sharks returned to the nursery within a few weeks or months after the hurricane passed. Our research, along with other studies, lead us to believe that there is something innate about the behavior of sharks to evacuate shallow estuaries and head to deeper waters. Scientists have seen several species of fish and juvenile sharks leave these types of systems despite having never experienced a major storm or hurricane within their lifetime.

What other findings came out of the study that surprised you?

Several of our tagged sharks were detected on a different coastal array of listening devices that another group of researchers had set up over 50 mi (80 km) north of the estuary. The sharks moved up the coast of Florida and were detected swimming around the Ten Thousand Islands for weeks after they left the Shark River Estuary. It’s also cool that most of these individuals came back to the estuary and will probably leave for the ocean once they are big enough.

Is it physically possible for a shark to be swept up into a storm and then fall from the sky far the ocean?

While not impossible, it is unlikely that even a small fish or shark would be picked up by rotating winds or a waterspout and dropped. What is so dangerous about hurricanes for most aquatic animals isn’t the direct winds but rather the changes to the water. There are examples of storm surge moving large animals long distances into inland areas. But more commonly, storm surge and high rainfall drastically alter water temperature, water velocity, and salinity. Some animals may be more sensitive than others to these changes. Hurricanes also can reduce the availability of oxygen in the water for aquatic animals by bringing in lots of mud and decaying debris that can essentially cause suffocation.

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