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 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.
But scientists say not to be fooled by the numbers: Shark populations are on the decline, and the greatest threat has been overfishing.
As the top predators in the ocean, sharks affect everything below them, not only fish but coral reefs and sea grasses.
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.
"You can pick almost any shark or ray in Florida waters and make a case for it being in trouble," said University of Florida professor George 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.
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.
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 now.
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. 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.
Sharks get little respect outside the scientific community.
"They're thought to be on the same level as rattlesnakes and mosquitoes. They're something we don't want around because they bite and eat people. There's a lot of people who want to play on that myth and trump up the fear factor on sharks," Hueter said.
They're not hot-button issues in Florida like grouper, red snapper, snook and manatees, yet sharks are critical to the long-term health of seas around the world.
"The public perception of sharks is still an educational process to convince people that No. 1, sharks are in trouble, and No. 2, that they're worth worrying about," Hueter said.
While scientists and commercial fishermen disagree about the status of shark stocks, research has shown what can happen when they disappear.
Hueter said shark populations in the Caribbean have been decimated by overfishing. Studies showed the absence of sustainable shark stocks affected the balance of the entire food chain, down to creatures that ate algae off the reefs. Eventually, the imbalance caused a coral reef to die, Hueter said.
"They're sort of the top dogs of the whole system," Burgess said. "As the top dogs, they influence a lot of what's going on down below them in the food pyramid."
Sharks have survived for 400 million years since the Devonian Period, "the age of fishes," Burgess said.
They are 100 million years older than dinosaurs.
"They're an ancient group, and they're still hanging around because they do what they do pretty good," Burgess said.