VIDEO, PHOTOS: Thousands of migrating sharks spotted along South Florida coast, beaches closed

PALM BEACH, Fla. - Seasonal visitors to Florida's Treasure Coast don’t all use Interstate 95. Some travel north to south using the currents of the Atlantic Ocean to carry them and water temperatures to guide them.

(See photos of Shark and babies caught along beach)

Tens of thousands of migrating sharks have been spotted by lifeguards, anglers and swimmers, and confirmed by television news helicopters. Shark scientists say that it is always good to be safe, but sharks are much closer to us than we think on a regular basis, and the risk of a bite fortunately is quite low.

Steve Kajiura, a shark researcher with Florida Atlantic University’s Elasmobranch Research Laboratory in Boca Raton, said Treasure Coast and Palm Beach swimmers may not know it, but during the months of January and February, a shark is only an average of 60 feet away.

“There are thousands of sharks right there, and yet this year, there have been no bites in Palm Beach County waters,” he said. “Our data has shown that the bulk of the migration occurs in January and February, but it may be a little behind this year due to the warmer weather and water temperatures.”

Kajiura and graduate student Shari Tellman have conducted aerial surveys of the waters between Boca Raton and Jupiter Inlet every two weeks. They fly a fixed-wing aircraft at 500 feet at about 90 mph and record video of the region from two feet of depth to about just over 30 feet of depth.

His data is eye-opening.

This time of year, they observe some 15,000 sharks each day, a density of 1,000 sharks per square kilometer, swimming north to south at an average of 200 meters from shore. Kajiura said they see them with the bait fish schools. Species observed include mostly blacktips and spinners, but also species such as hammerheads, tigers, lemons and bulls. They also see manta rays, manatees and other fascinating sea life.

Kajiura reminds visitors and residents that sharks do not seek humans as food sources.

“It is surprising to think there may be a shark swimming 60 feet away from us, but they are not out to get us,” he said.

The sharks, Kajiura explained, are headed north, but will distribute along the eastern coast of the United States as far north as North Carolina. Other species of sharks occur in greater numbers along the Treasure Coast and Palm Beaches at different times of the year. Lemon sharks gather in deep water near Jupiter each May for what is believed by scientists to be a mating period. Tiger sharks, according to research conducted by former Harbor Branch scientists, occur in much greater numbers along the Treasure Coast from May through August to coincide with the peak of the sea turtle nesting season, which they feed upon.

For the time being, red flags may be a more common sighting at area beaches, as lifeguards protect swimmers from sharks.

In Martin County, about one beach a week is being temporarily closed because of shark sighting or signs that they were there, said Martin County Ocean Rescue Captain Emily Hall.

The only suspected shark bite in the area in 2013 occurred Feb. 10 near Chastain Beach, known as “The Rocks” by surfers. Cole Taschman, 16, of Jensen Beach was surfing when he was bitten on the hand. He received 12 stitches at Martin Memorial Hospital.

Martin County's ocean waters are murky, making it hard to see sharks unless they are close, Hall said Wednesday.

Sometimes, surfers see the sharks before anyone else and alert lifeguards, who usually close the beach to swimming for about 30 minutes, or until it appears there is no threat.

Most of the closings were during January, when there were 14 at Jensen Beach, five at Hobe Sound and three at Stuart Beach, she said.

During February, there were a total of five closing between all the beaches.

So far this month, there has been only one confirmed sighting of a shark at the public beaches, she said.

Because of the murky water, she said it is hard to say which species of sharks are out there.

St. Lucie County lifeguards have spotted a couple of sharks off South Hutchinson Island but so far there have been no problems at the beaches, county spokesman Erick Gill said Wednesday. If sharks do come in to feed in the surf, lifeguard caution people to beware, he said.

Spinner sharks can be seen jumping out of the water and spinning as they chase their prey through the water.

Capt. Bruce Hrobak, owner of Billy Bones Bait and Tackle stores in Port St. Lucie and Stuart, said the showing of sharks is a good sign for offshore anglers.

“They are swimming with migrating schools of bait fishes like threadfin herring and sardines, and that will mean an upswing in all kinds of fishing action,” he said. “I’ve heard of some spinners and blacktips near the inlets.”

Although they're an interesting sight to see, sharks are quite dangerous to swimmers. Doctors at St. Mary's Medical Center say they treat at least five to six shark bite victims a year. They say the injuries are usually minor, but even small shark bites can put victims