Shark sightings shut down Cape Cod beaches

(CBS News) Beach goers in Cape Cod, Mass. found themselves with some unwanted company this Labor Day weekend.

Two sharks were spotted, prompting officials to raise the red flag, banning swimming at some of the areas most popular beaches. From South Beach in Chatham, to the northern tip of Nauset Beach in Orleans, shark sightings are keeping bathers out of the water.

One swimmer said, "Someone told me they can't come close to the edge, but I don't believe that anymore, so I'm just staying out."

The sightings aren't the first of the summer. In July, a man bodyboarding off Truro said he was bitten by a great white shark, the first known attack in those waters in over 75 years. He survived, but the incident led many to question why so many sharks are lurking off the cape.

Biologist and shark expert Simon Thorrold said the sharks are likely responding to an increased number of mammals - but not of the human variety.

"I think we're probably seeing more white sharks in the area at the moment," Thorrold said. "And the white sharks have probably been drawn into the area by a really large increase in the number of grey seals that are in the area."

That suspicion may have been confirmed this week when a family captured dramatic video of a shark attacking a seal off Monomoy Island.

Seals are a staple of a shark's diet. It is estimated 350,000 of them live along the North-Atlantic coast. They have been protected since the 1970s by the federal Marine Mammal Protection Act.

With the resident seal population showing no signs of slowing down, beach goers will have to share the shore with the sharks... at least until the great whites migrate to warmer waters this winter.

For Terrell Brown's full report, click on the video player above.