BOSTON -- Cape Cod officials are considering closing some beaches after more great white sharks have been spotted this week.

On Wednesday alone, there were three more shark sightings off Chatham, officials said.

The shark sightings have left officials considering closing some east-facing Chatham beaches on Thursday.

"It would be South Beach and or North Beach Island. The majority of the reports and the sightings appear to be off South Beach, about 2 to 3 miles south of the lighthouse," said Harbormaster Stewart Smith.

Also on Wednesday, a professional fish spotter saw one of the fish, a 1,500-pound great white, about 100 yards off shore and about 20 feet from an unsuspecting swimmer.

"It's terrifying in the airplane. I've seen this on a couple of occasions where the shark will swim directly at a swimmer and then he'll veer off, you know. He probably senses there's something in the water, maybe it's dinner, it's a seal," said spotter George Breen.

In fact, the burgeoning population of gray seals off the Chatham coast is what's thought to be attracting the sharks. The once-endangered population has grown, making for a big attraction for the predators.

"We've seen two or three dead seals this year, with a shark implicated in its demise," said Greg Skomal, a state biologist with the Division of Marine Fisheries.

The danger comes when humans swim near the seals. The crew of Breen's boat, the Easy Does It, managed to tag the shark that came in close in order to monitor and study it.

"Just have to exercise caution. That's why we're doing the scientific research. Putting the tags in. Finding out their habits. When they come in shore, what tides, what water temperatures," said Breen.

Even if beaches remain open, officials said people should stay near shore and not venture close to seals.