Thousands of sharks on their annual migration north have closed beaches along the southern Florida coast.
Beaches along the southern coast of Florida are on high alert after sharks were spotted near shore as part of their annual migration.
Many beaches had red flags flying on Thursday morning to alert people, but some beaches had reopened.
Sharks were spotted near three beaches in Palm Beach County on Wednesday, but they had reopened on Thursday morning, The Palm Beach Post reported. However, Steve Kaes, a lifeguard training officer, told the paper that he couldn't guarantee that the beaches would remain open throughout the day. If someone spotted a shark, swimmers would be asked to come out of the water, he said.
Sky News reported that many South Florida beaches were shut down after thousands of migrating sharks were spotted near shore.
Shari Tellman, a researcher at Florida Atlantic University's shark lab, told MSN News that the sharks – mostly black tips and spinners – come down during fall as part of their normal migration pattern north. They were usually gone by April, she said.
"They are like snow birds, they come down to get to warmer water," Tellman said. "The reason we see them in such high numbers in Palm Beach County is because they congregate close to shore as the offshore shelf narrows and feed on the baitfish."
Tellman said that although the sharks don't attack swimmers, they have sharp teeth and could bite people in murky water.
"These sharks have been blamed for bites and scrapes," she said. "It's a good idea to close down the beaches to give them some space."
Some students on spring break are opting to stay out of the water altogether, according to ABC News.
Tellman said that researchers at the university had counted 5,000 to 6,000 sharks during their last aerial survey, most of them less than 200 yards from shore.
"There's no way to figure out the entire population because you can't see them all," she said. "We try to get a relative abundance over a period of time so that we can compare it with future migrations."
Tellman said she and other researchers wanted to tag the sharks to "track their actual path."
"With ocean temperature rising, it will be a good way to get an idea about how climate change might affect the migration," she said.
Pictures taken by Jeffrey Langlois of the Palm Beach Daily News show the sharks, mostly blacktip and spinner sharks, coming close to the shore.
"We saw something moving in the water and everybody was saying, 'oh shark,'" one witness in Palm Beach told ABC News.
About 50 to 60 sharks were spotted near the shore in Palm Beach on Tuesday.
Lifeguards in Palm Beach told ABC News that the sharks for the most part don't disturb the beaches.
"We don't have a sandbar. A lot of times when we have a sandbar the sharks stay off of the shore a little further," Craig Pollack, a lifeguard supervisor in Palm Beach, told ABC News.
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