Scientists at the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science are challenging the status quo on what we know about sharks and hurricanes. Sharks — and other marine life — are sensitive to barometric pressure, which drops when a major storm like a hurricane comes in. Research has shown sharks can actually feel the change in pressure and swim out to deeper water to where they feel they will be safer. “How these storms impact the environment, including large sharks, is of interest and conservation concern to many,” said Dr. Neil Hammerschlag, a research associate professor at the UM Rosenstiel School and the Abess Center for Ecosystem Science and Policy who is also the director of the University’s Shark and Research Conservation Program.
The recent onslaught of extreme weather due to climate change has given scientists ample opportunities to study this phenomenon. Afterall, there are still a lot of questions of how a shark weighs up the risks when a hurricane is heading its way. “When these big storms come through, you have a lot of wind, a lot of waves—a real chaotic environment,” marine scientist Grace Casselberry, a doctoral candidate at the University of Massachusetts Amherst, told Hakai Magazine in 2019. Casselberry and her colleagues were tracking a variety of sharks (tiger, lemon, nurse, and Caribbean reef sharks) off northeast Saint Croix in the US Virgin Islands when Hurricane Maria hit in 2017. They’d attached transponders to the sharks that sent signals to receivers that were anchored to the seafloor which survived the extreme storm and recorded how the sharks behaved. Nine of the sharks, including individuals from each of the four species, moved towards deeper water. “We think they’re moving out to these deeper areas to take shelter from the storm.”
The UM researchers found something similar when they analyzed acoustic tag data from tiger sharks (Galeocerdo cuvier), bull sharks (Carcharhinus leucas), nurse sharks (Ginglymostoma cirratum), and great hammerheads (Sphyrna mokarran) before, during, and after Hurricane Matthew in 2016 and Hurricane Irma in 2017. But they also found that the sharks behaved differently depending on their species and location. Published in the Estuarine, Coastal and Shelf Science journal, the team showed that bull sharks, great hammerhead, and most nurse sharks appeared to mostly evacuate the shallow waters of Biscayne Bay when Hurricane Irma passed by Miami. This wasn’t too much of a shock since similar previous studies have shown little sharks evacuating the safety of these inshore shallows in the wake of a storm.
But the big sharks? Well, they might ride the storm out. The team found that large tiger sharks in the Bahamas remained in the shallows, even as Hurricane Matthew raked across island nation, leaving a trail of damage behind. Underwater, the tiger sharks stayed put… and immediately following the storm, their numbers doubled. “I was amazed to see that big tiger sharks didn’t evacuate even as the eye of the hurricane was bearing down on them, it was as if they didn’t even flinch,” said Hammerschlag. The scientists suspect tiger sharks were probably taking advantage of the dead animals left over by the storm, providing new scavenging opportunities.
Observations like these can help scientists understand how shark populations can change in size and distribution due to natural disturbances, proving useful as science shows major storms, like hurricanes, are predicted to increase in frequency and strength with climate change.
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