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Florida prof. determines start, end of shark season

The photos are remarkable. Snorkelers just feet away from more than a dozen sharks. Another group of sharks surfing off Fort Lauderdale Beach.

And there is the video - downright amazing. Thousands of sharks lurking just off South Florida's shoreline.

Stephen Kajiura, a professor at Florida Atlantic University, is captivated by it all.

"It's terrifying for some people. They say 'Wow look at all those sharks that are there. I'm not going to get in the water'," he told CBS News Miami.

Kajiura has been capturing the images of the sharks for five years. His bi-weekly flights are part of study to track shark migrations.

"These sharks are snowbirds. They do exactly what our visitors do from the North," Kajiura explained.

The videos confirm sharks arrive here starting in January. And by this time of the year, mid-April, they are on their way out.

What Kajiura discovered during the course of his study was the ability to predict exactly when they arrive and leave.

"Sharks are very attune to temperature," he explained. "And they are only here in a narrow temperature band of 21 to 24 degrees Celsius."

That's 69 to 75 degrees Fahrenheit.

"You see them right off Miami Beach, Fort Lauderdale, Port Everglades, all the way up through Palm Beach. There are certain pockets, there are more sharks and areas where there are fewer," Kajiura said.

The aerial surveys show sharks hangout mostly around inlets, especially Miami's Government Cut, Haulover, Port Everglades and Jupiter Inlet. They are hotbeds for shark activity because that is where lots of fish swim in and out every day.

"It's like the sharks' little grocery store," he said. "They get to hang out and wait for the food to come to them."

Kajiura's research was supposed to be shut down last year. But when a secret donor read about it closing, that changed.

Kajiura not only received funding to keep flying, he got a whole lot closer to the sharks.

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"The flying gives you the opportunity to look and see where the sharks are distributed. And once you know where they are you go and target your fishing."

Early Sunday morning he boards a center console boat with a crew of FAU students. They lay out a series of hooks just feet offshore.

Using his aerial surveys he knows exactly where to go. Fisherman would say that's cheating.

Kajiura's response? "That's taking advantage to the options available to me."

Most people would be surprised to see him fishing so close to shore. Kajiura agrees.

"It really is no more than one or two football fields off shore," he said.

That's because that's just how close the sharks are. Within minutes they have their first catch.

The team jumps into action doing all kinds of measurements and recordings. It's one thing to count sharks, but Kajiura wanted to know more. By catching sharks he can find out what kinds of sharks are here, how big are they and are they boys or girls. The answer surprised everyone. Kajiura laughs.

"We've only caught males, 100 percent of the sharks we caught are males down here," he said.

That of course raises a new question; where are the girls? They are hoping tiny transmitters inserted into the bellies of these sharks will give them the answers.

Up and down the Eastern seaboard there are receivers in the water. And every time one of these transmitters comes by, they pick it up. They are able to track these sharks as far as North Carolina and parts beyond.

If all this gives you the heebie-jeebies, Kajiura has good news - shark season is over.

"These sharks are going to start appearing again in January. So about a year from now," he says.

Kajiura plans to do his study for another two years then take a break.

Ideally he wants to revisit the flights in a decade to see what changes have taken place.