LAKELAND — When the Deepwater Horizon oil rig disaster spewed nearly 5 million barrels of oil into the Gulf of Mexico during the spring and summer, sharks were pushed ever closer to shore.

“Some species were almost being herded into some beaches because oil was coming in,” said Dr. Bob Hueter of Mote Marine Laboratory in Sarasota.

The oil spill pushed sharks toward the beaches in the Panhandle and may have caused an increase in the number of sharks off the Tampa Bay area this summer, including a rare appearance by massive whale sharks just 10 miles off Sarasota.

But scientists say not to be fooled by the numbers: Shark populations are on the decline, and the greatest threat has been overfishing.

Feared as man-eaters but pursued by fishermen for the price of their fins and meat, the thrill of the catch and even world records, sharks also are vital to ocean ecology. As the top predators in the ocean, they impact everything below them, not only fish but coral reefs and sea grasses.

Sharks are part of the elasmobranchs family along with sawfish, rays and skates.

They have adapted and evolved over the past 400 million years, but heavy fishing pressure in the last two decades of the 20th century heightened concerns among scientists like Hueter that the continuing depletion of sharks would disrupt the entire food chain.

“Just like on land, when you remove apex predators, the effect cascades through the food web, throwing everything out of balance and leading to changes,” Hueter said. “It takes decades for them to come back.”

University of Florida professor George Burgess said populations of many shark species are declining in Florida and worldwide because of several factors:

Their fins are highly coveted in some parts of the world, selling for more than $12 an ounce in Hong Kong.

They’re snagged by shrimp trawls, gill nets and longlines, which are spread along the sea floor with miles of baited hooks intended for species like grouper, tuna and swordfish.

They’re losing habitat in estuarine nursery grounds where their pups are born.

“You can pick almost any shark or ray in Florida waters and make a case for it being in trouble,” said Burgess, director of the Florida Program for Shark Research in Gainesville.

Quantifying exact shark numbers is not possible. But Hueter, director of the Center for Shark Research at Mote Marine, said shark stocks around Florida have dropped about 50 percent since 1975 primarily because of overfishing by commercial boats, and to a lesser degree recreational fishermen.

Science disputed

Commercial fishing interests dispute scientists’ contention that shark populations are in decline.

Russell “Rusty” Hudson of Daytona Beach, a consultant for commercial fishermen, disagrees with the science the National Marine Fisheries Service relies on to set regulations in federal waters, rules that have effectively halted large-scale commercial shark fishing for the past two decades.

“The reality is that the fishermen feel the pressure of being ratcheted down, and the pressure of what we call incomplete science,” Hudson said.

For instance, Hudson said sandbar sharks are so prolific 10 to 40 miles off Daytona Beach that they are eating red snapper and amberjack off recreational anglers’ hooks as they reel them in.

“The sandbar sharks are coming back strong and heavy,” said Hudson, president of Directed Sustainable Fisheries.

But Hueter, the Mote Marine researcher, pointed out that sandbar sharks, which accounted for 40 percent of the commercial take in 2000, are a prohibited species and not one of the 33 species commercial boats can harvest now.

The Florida Fish and Wildlife Conservation Commission has been a national leader in protecting sharks in state waters since the early 1990s.

And with strict regulations from the NMFS in federal waters, commercial fishermen around Florida can’t depend solely on sharks to make a living. “You can’t do it. Everything’s so regulated now,” said Dane Karcher of John’s Pass, a charter captain who once fished for sharks commercially.

John Carlson of the fisheries service said not all sharks in the Gulf are dwindling, the blacktip being a prime example of an abundant species.

“There are some populations of sharks which are not in very good shape, but there are some whose populations are sustainable,” Carlson said.

Huge hammerheads, as well as bull sharks, are so prevalent at Boca Grande in May and June that charter captains are afraid to lean into the water to release tarpon.

Yet the numbers of some sharks have decreased dramatically, and a boost in population in one area doesn’t mean the overall numbers are improving.

Dusky sharks, which Carlson said don’t reach maturity until they are 20 years old, have plummeted 80 percent in the Gulf from levels prior to commercial harvest and are listed as a prohibited species. Great hammerhead sharks are down 70 percent since 1980.

“Hammerheads appear to be abundant in focused places like Boca Grande in the springtime when the tarpon are there. But when you look over the breadth of their range, they’re not as abundant as they once were,” Hueter said.

The small-toothed sawfish, a member of the rays family found primarily in the Everglades, is in considerable trouble, said Burgess. It was the first marine endangered fish species in the U.S.

“When these animals, whether they’re sharks or sawfish or rays, get knocked down, it’s going to take a long, long time for them to return even under the best of management strategies,” Burgess said.

“We’re going to have to hope that our sons and daughters and grandsons and granddaughters are going to carry the torch for the next couple of generations.”

One-shark rule

Florida has been at the forefront of protecting sharks since 1992, when the Florida Fish and Wildlife Conservation Commission banned finning, instituted a one-fish-per-person daily limit and prohibited the catch of almost two dozen overfished or rare species.

“Florida was the leader in fishery management for sharks long before other states and even the federal government did,” Burgess said. The one-shark-per-person rule “more or less put commercial fishermen out of business in state waters,” he said.

In mid-January, the FWC added three more species to the protected list, including sandbar sharks.

The FWC also:

n Established a 54-inch minimum length in January for all but six species, including blacktips, bonnetheads and the Atlantic sharpnose.

n Prohibited removal of heads and tails at sea.

n Restricted gear to hook and line.

n And on March 23, the FWC made it illegal for recreational or commercial fishermen to take lemon sharks, which don’t reach sexual maturity until they are 12-15 years old.

Hudson, the consultant for commercial fishermen, said commercial fishing for sharks has been limited to a recreational catch for the past couple of decades, and the number of permits sought is now about 90 percent less than it was in 1999.

“To just use a blanket expression, we’ve managed commercial fishermen out of business,” Hudson said.

In federal waters, starting at nine nautical miles in the Gulf and three miles off the Atlantic coast, sharks are regulated by strict quotas and trip limits.

Commercial fishermen could catch 4,000 pounds per trip until 2008, but now the maximum is 1,000 pounds, or 33 sharks.