Transcript for Experts warn of shark boom off Cape Cod

Next tonight, the scare in the water. Authorities warning swimmers about the great white shark population,xp ding O inn destinati destination. Warning for possible shark attacks. Here's ABC's gio Benitez. Reporter: Tonight, the numbers tell the story. Off the coast of cape cod alone 150 great whites are expected this summer. In 2014, there were about half that. Already this month, we've seen this shark possibly a great white, lurking right next to a fishing boat right there. This 14-foot great white was tagged there a few years ago -- and was just detected near Virginia's coast on Sunday. Cape cod first responders now training for shark attacks, and posting these signs warning beach goeers. They say the growing seal population, what sharks feed on, is to blame. The probability of a shark attack is extremely low. But it doesn't mean you don't use common sense when you're going into the ocean. Reporter: They're hoping to avoid scenes like this. People screaming to get out of the water at this Alabama beach two weeks ago, spotting sharks in the shallow water. And Tom, expers say there are a few things you can do to avoid sharks on beach, swim on sunny, clear days, but not at dawn or dusk -- that's when shark feed.

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