Florida beaches are closed for a fourth time in the past month, as a massive number of sharks swarm the state's Atlantic coast.

On Tuesday, thousands of sharks circled just a few hundred feet from shore off Juno Beach, just north of Palm Beach.

Slideshow: Thousands Of Sharks Spotted Off Florida Beach
Video: Thousands Of Sharks Spotted Off Florida Beach
E-Mail: Send Shark Story To A Friend

Biologists believe the sharks are probably spinner sharks, which are seen this time of year in shallow water.

The sharks are looking for food -- fish, squid, rays, and other sharks -- before migrating north for summer.

In the past month, sharks have forced beachgoers to avoid the water in Delray Beach, Deerfield Beach, Boca Raton and Palm Beach.

Last Tuesday, Deerfield Beach was closed to swimmers and surfers after hundreds of migrating sharks were seen swarming close to shore in South Florida.

Slideshow: Sharks Force Closing Of Fla. Beaches
Sharks Swarm Off Fla. Coast

From the air, hundreds of sharks could be seen about 100 to 200 feet away from shore at Deerfield Beach. No injuries have been reported from the sharks in this most-recent incident.

City officials said they closed the beach as a precaution.

On March 18, a large group of sharks also was spotted swimming close to the shore at Delray Beach, a week after a similar incident.

Slideshow: Sharks Swarm Near Another Popular Fla. Beach

In that incident, officials put up red flags in the area to keep swimmers out of the water.

Experts said sharks congregate off South Florida every year in March and April to feast on sardines, herring, anchovies and other fish before migrating as far north as New Jersey.