ORLEANS, Mass. — Shark sightings prompted Massachusetts officials to close two beaches to swimming.

The first sighting was off Nauset Beach in Orleans on Saturday morning. The Atlantic White Shark Conservancy says there was a confirmed attack on a seal by a great white shark just before 10 a.m. Saturday. Swimming was prohibited for about an hour.

The conservancy says another shark was spotted by a lobsterman off Plymouth at about noon, which prompted officials to close town beaches for three hours.

Several Cape Cod beaches have been temporarily closed to swimming this summer because of shark sightings.

Surveillance has been stepped up this summer after two shark attacks on humans off Cape Cod last year, including one that killed a 26-year-old Massachusetts man.