Experts said a cluster of some 20 great white sharks was recently spotted by the U.S. Coast Guard off Northern California's coast.
The San Francisco Chronicle reported Saturday the sharks were seen swimming together last week about 100 yards offshore near the city of Pacifica.
Gulf of the Farallones National Marine Sanctuary spokeswoman Mary Jane Schramm said two Coast Guard helicopters flying 500 feet above the ocean spotted the group on Oct. 16.
Schramm said most of the sharks were between 10 and 15 feet long and a couple of them were about 18 feet long.
The region's sharks can grow up to 21 feet and weigh as much as 7,000 pounds. They typically return from the deep ocean to feed at the Farallon Islands this time of year.