Place with the highest density of sharks in the world

The Cape Cod area in Massachusetts had an estimated 800-900 sharks swim through it in 2015-2018, possibly reaching the highest shark density in the world .

Great white sharks swim close to shore at Cape Cod. Photo: National Geographic — Great white sharks swim close to shore at Cape Cod. Photo: *National Geographic*

The number of sharks lurking in Cape Cod waters is difficult to determine because counting the elusive animals over such a wide area is complicated. But researchers at the Atlantic White Shark Conservancy have found the answer using a combination of acoustic monitoring, photographic identification, and statistical modeling.

According to the study, there were between 800 and 900 sharks swimming in Cape Cod waters from 2015 to 2018, according to National Geographic . For comparison, the estimated population of white sharks off the coast of California is 300. "Cape Cod's shark density is likely the highest in the world," said Megan Winton, a fisheries scientist who collected the data.

The discovery is significant not only because of the sheer number of sharks, but also because they are concentrated along more than 900km of coastline. Four years of monitoring also revealed that the sharks, mostly adults measuring 2.4-3.7m in length, spend about half their time in waters less than 4.6m deep.

“People may know that great white sharks come here, but they think they’re far out at sea,” Winton said. “We’ve seen sharks up to 15 feet long in waters that are only 4 to 5 feet deep. Their camouflage is incredible. People can be right next to them and not see them.”

Great white sharks are thriving again on Cape Cod for a simple reason. Their favorite prey, the gray seal, is recovering. Hunted to near extinction, the seal population began to rebound with the passage of the U.S. Marine Mammal Protection Act in 1972. Today, there are 50,000. Great white sharks, once listed as vulnerable by the International Union for Conservation of Nature, took longer to recover. But thanks to national protection in 1997 and in Massachusetts in 2005, their numbers have steadily increased in the eastern United States.

According to Greg Skomal, a fisheries scientist at the Massachusetts Division of Marine Fisheries, the risk of a shark bite is very small, and swimmers are more likely to drown. There have been only five shark bites on Cape Cod since 2012, including one fatal incident in 2018. To reduce the risk of shark-human encounters, scientists need to know where and when sharks swim.

To find out, the Cape Cod team cataloged sharks from 2015 to 2018, identifying them by tagging or photographing their dorsal fin color and shape. They then conducted three years of surveys, comparing newly photographed sharks with those already recorded, and reconstructing encounters using statistical models to come up with population estimates. Unlike previous surveys in South Africa, California, and elsewhere, Winton’s model takes into account shark movements. The new model allows for consideration of where sharks like to congregate along coastal areas.

Using high-quality portable underwater cameras makes shark identification easier and more accurate. In addition, experts at the Center for Coastal Studies on Cape Cod also use sonar surveys to map shark movements.

Great white sharks are ambush predators, usually lurking in deep water and launching themselves high into the air to surprise their prey. But along the coast of Cape Cod, sharks are forced to hunt in shallow water. They do so by circling the sandbar depressions, waiting for hungry seals to come out to feed. Understanding this unusual behavior helps experts predict shark movements and identify areas that are particularly dangerous for swimmers.

Since 2009, the Cape Cod team has tagged a total of 303 sharks with sonar transmitters. Five of the trackers can detect sound pulses as tagged sharks swim by, transmitting real-time information to lifeguards, beach managers, scientists and the public via an app.

An Khang (According to National Geographic )

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