A massive aggregation of blacktip sharks has invaded the waters around the Jupiter Inlet of Palm Beach County, Florida, with an estimate of more than 10,000 of them, many swimming just yards off the beach.

"It seems the sharks really like Palm Beach," Stephen Kajiura, a professor of biological sciences at Florida Atlantic University, told the Orlando Sentinel. "They like Palm Beach County for some reason."

Kajiura explained to the Sentinel that it could be because of the near-shore narrowing of the continental shelf funnels sharks close to shore whereas it is much broader further north.

"That's why we have this huge number, Palm Beach area and south, where you simply don't have them up north," Kajiura said. "They're there, but they're probably distributed over a much broader area and so you just don't see those large dense aggregations that you see down here."

Another reason they are close to shore could be the presence of mullet and menhaden, Kajiura suggested.

Kajiura, who has been taking aerial surveys of the annual blacktip migration, takes to the air once a week starting in December to look for the sharks. His team also fits some of the sharks with acoustic transmitter tags for research.

"This is a particularly compelling migration, because it happens so close to shore in such clear waters, and because it happens in such a popular winter destination for people," Kajiura told the Christian Science Monitor. "We know that other shark species migrate, but you don't have that same visceral connection with people able to observe so nearby."

So what is the likelihood of a shark attack with so many sharks so close to shore? Minimal. No blacktip shark bite has ever been fatal. And anyway, they tend to stay away from people, Kajiura said.

"The sharks are not out to get you, and if they wanted to bite you, there'd be ample opportunity," Kajiura told the Christian Science Monitor. "But in this clear water, they can easily see you're a human, not a fish. Besides, these sharks are skittish, and they'll likely swim away, even if you try to get close."