An alert has been issued to swimmers after hundreds of sharks up to 10 feet long were spotted this week off central Florida's west coast.

Bull sharks, hammerheads and nurse sharks were among those sighted by sheriff's marine patrols in the shallow Gulf of Mexico waters off Pasco County, northwest of Tampa, officials said Tuesday.

Pasco County Sheriff's Office spokesman Kevin Doll said the sharks were first sighted Monday. No one has been bitten.

Shark attacks and sightings continue to make headlines this summer. An 8-year-old was attacked by a 7-foot bull shark, which tore off his arm, at Gulf Islands Seashore in the Florida Panhandle. And a New York man lost his leg to a shark in the Bahamas.

Terri Behling, a spokeswoman for Mote Marine Laboratory in Sarasota, Fla., said it is too early to speculate what might be luring the sharks. Experts first need to determine the sharks' species and size, she said.

Behling said it is not unusual for sharks to swim up and down the gulf coastline, following tarpon. But a congregation of different species is unusual, she said.

Sean Paige of the Competitive Enterprise Institute, which advances the principles of free enterprise and limited government, was interviewed on Hannity & Colmes Tuesday about his research into government protection of sharks.

The federal government in 1997 slashed its quota for shark-fishing in half, after government studies showed the ocean predators were overfished.

"This may be one federal program that's actually working, and it's gotten measurable results because every year the government has reduced the amount of sharks that can be caught," Paige said. "That leaves more sharks in the water.

There are state programs, including those in Florida, to protect sharks as well, Paige said.

"In Florida, you have a shark sanctuary in state waters," he said. "That extends three miles out in the Atlantic and nine miles into the Gulf. The other thing is Florida in 1995 passed a gill-net ban in Floridian waters. That stopped any fishermen from catching mullet. Mullet are a favorite food of all sharks. You may have actually too many fish — too many bait fish in close to shore. That's drawing the sharks in closer."

The Associated Press contributed to this report.