Beaches were closed at Deerfield Beach and Delray Beach after lifeguards spotted the sharks just offshore, the South Florida Sun-Sentinel reported Wednesday.
Some of the sharks were sighted as close to shore as 20 feet, but there were no reports of attacks.
George Burgess, director of the International Shark Attack File at the University of Florida, said the sharks are not man-eaters but have been known to bite people whose splashing hands or feet are mistaken for food.
He said blacktips and spinners grow to be about 7 feet long and eat small fish.
Last year, 12 shark attacks were reported in Florida, which leads the world in shark attacks. In 2003 there were 30 attacks.
Burgess said attacks may have been down last year because the four hurricanes kept swimmers out of the ocean and sharks away from shore.