Chatham, Massachusetts — Tourists are heading to Cape Cod for the Fourth of July weekend and waiting close to shore are 11 great white sharks spotted over the last two days. Marine biologist Greg Skomal tagged three of the great whites spotted off Cape Cod.

This wasn't Skomal's first close encounter with jaws. Last year, a great white nearly snatched him off his research boat. Social media this year has featured video of sharks terrifyingly close to swimmers in Florida.

Marine biologists think the main reason they're seeing more sharks off the East Coast is an abundance of food. Since becoming a protected species, the gray seal population off Cape Cod has exploded.

"We think it really is as simple as a larger number of seals, more sharks coming closer to shore to feed on the seals," Skomal said.

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In Orleans, Massachusetts, fire chief Anthony Pike has added landline phones because of bad cell reception and first aid boxes are on the beach for dealing with severe injuries.

"This is a natural hunting ground for this species. Take into consideration that you are a land animal going in the ocean and be vigilant," Skomal said.

Shark bites are still very rare. But if people at the Cape want to keep an eye on their favorite beach, there's an app for that. It's called Sharktivity and it plots shark sightings.