Several reports of shark bite injuries and a spate of sightings of the marine predators off the Northeast coast of the United States have rattled summer beachgoers.
But are New York's Long Island and Cape Cod, the peninsula of Massachusetts, where many of the recent suspected shark encounters have taken place, experiencing anything exceptional?
Yes and no, according to Gavin Naylor, director of the Florida Program for Shark Research at the University of Florida in Gainesville.
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Globally, shark attacks are at similar levels to previous years, said Naylor, who is also a curator of the Florida Museum of Natural History, but there are signs that the Northeast coast of the US might be seeing an uptick.
"We are right on trend for this time of year. I think globally, we usually get between 70 and 80 unprovoked bites by sharks around the world.
"But that's a global phenomenon. And it's distributed in a patchy way," Naylor explained.
"One year we might have two or three bites in Hawaii in rapid succession. Next year, it could be New Caledonia; it could be in Western Australia. And this year, it's off the coast of Long Island."
Naylor declined to give the year-to-date totals so far, saying it takes time to investigate and authenticate reported bites. (Naylor's work at the Florida Museum of Natural History involves tracking data on shark attacks.)
Last year, there were 73 confirmed unprovoked cases of shark bites — in line with a five-year average of 72 incidents annually.
There were 11 shark-related fatalities, however, up from an average of five per year.
Fish, not humans
The sharks that swimmers have encountered off Long Island were seeking out food, not targeting humans, Naylor explained.
Most have been identified as sand tiger sharks, Naylor said, which, while fearsome looking, aren't considered aggressive.
They have likely been venturing into coastal waters to prey on abundant shoals of bait fish close to shore.
The shoals were particularly dense this year because of warm ocean currents peeling off from the Gulf Stream in the Atlantic Ocean and extending up the Northeast coast, he explained.
These waters are richer in chlorophyll, allowing plankton to bloom, which also draws in bait fish.
"These bait fish are in schools of hundreds of thousands — or millions," Naylor said, "and when they get quite close to shore, the sharks follow them.
"The sharks are swimming around trying to chase their dinner.
The people are swimming around splashing with beach balls in their circle.
The surf zone gets quite murky because of all the energy and the sharks are all jingled up because they're excited to see all this food — once in a while they make a mistake."
Contributing to the problem is a sand tiger shark nursery, discovered in 2016, off the coast near shore waters of Long Island's Great South Bay, where sharks ranging from several months to five years in age feed and grow.
(The sharks are born off the southeastern US coast before migrating north and spending their summer in New York waters and returning south again in the autumn, according to the Wildlife Conservation Society.)
Unlike adult sand tiger sharks, which are up to 2.7 metres long, the 1.2 to 1.5 metre-long juveniles may go closer to shore to chase fish.
"As you can imagine, (the) same with any mammals, juveniles aren't as experienced. They don't have as much pattern recognition skills as adults," Naylor said.
"We suspect strongly that it's the juveniles and their judgment and discernment between what is somebody's foot and what's a flash of a bony fish's scales.
"You've got a bunch of teenage sharks and they're running around chasing fish."
Great whites
Different dynamics have been at play off Cape Cod, where several great white sharks have been spotted this summer, prompting the closure of at least one beach. Naylor said there are no reports of shark bites, to his knowledge.
During summer and autumn, white sharks hunt seals — their preferred prey — along the region's shoreline, which can bring them close to popular beaches.
Based on tagging data from 14 sharks, a study released last year in the journal Wildlife Research found that they spent almost half their time at depths of 4.6 metres or less.
This means there is a high potential for their presence in recreational waters frequented by swimmers and surfers.
"Until now we didn't know just how much time they spent in shallow water close to shore," said lead author Megan Winton, a research scientist at the Atlantic White Shark Conservancy, in a news release last year.
The North Chatham, Massachusetts-based nonprofit provides funding and resources for scientific research to improve public safety.
The population of great white sharks off Cape Cod has increased in tandem with the local seal population, which rebounded in the decades following the Marine Animals Protection Act of 1972.
It's the only place in the Atlantic Ocean where white sharks congregate.
To date, around 300 white sharks have been identified and tagged by researchers, but there's no official population estimate yet.
Since 2012, there have been four unprovoked attacks by white sharks on humans along the coast of Cape Cod, including one fatal attack in 2018, the first in Massachusetts since 1936.
No matter what type of shark, Naylor said the measures to protect yourself are similar: Don't swim or surf on your own, and don't swim near big shoals of fish or if you spot seals nearby.
Don't wear jewelry in the water that a shark could confuse for the shimmer of fish scales. If you do spot a shark, back out of the water slowly. Don't panic and splash around.
