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Sometimes sharks cooperate, sometimes they don't
Sometimes sharks cooperate, sometimes they don't: Scientists from the Mote Marine Laboratory often tag sharks, and sometimes it works as it's supposed to. Tagging a blacktip shark went well, but a hammerhead shark was not so cooperative. By Kevin Lollar/news-press.com

Tracking sharks online

Click here for a link to track sharks tagged by Florida Gulf Coast University and the University of Florida.

You can follow 10 sharks tagged off Lee County, two bull sharks, named Chloe and Hoover, and eight tiger sharks, named Ash, Chuck, Domski, Kelli, Ray J, Sophi, Sweet Caroline and Virginia.

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In baseball terms, the scientists went 0 for 85 last week.

Over two long days, scientists from FGCU and the University of Miami soaked 85 baited hooks off Fort Myers Beach in an attempt to catch bull, great hammerhead and tiger sharks.

They didn’t get a bite.

“We’ve never been skunked with that many baits in the water,” said Bob Wasno, education and resource coordinator at FGCU's Vester Field Station. “You’d think we would have snagged one just swimming by.”

These trips were part of two ongoing research projects.

FGCU professor of marine science Darren Rumbold is studying mercury in sharks, while University of Miami scientists are conducting a behavioral ecology study of the three shark species.

To catch their target species, the scientists use shark-friendly gear known as drum lines.

A drum line starts with 40-pound weight with an eye bolt at the top.

Attached to the eye bolt is 70 feet of 900-pound monofilament line, at the end of which is a 16/0 circle hook — circle hooks catch fish by the lip or jaw instead of the gills or gut.

Many shark species need to swim to pass oxygen over their gills, and the long line lets a hooked shark circle until it is brought to the boat.

Essential to the research are smart position or temperature tags, which send a shark’s position to a satellite every time the animal surfaces.

Since 2010, the University of Miami has tagged more than 80 tiger, bull and hammerhead sharks in the Keys, the Bahamas and Hawaii.

FGCU bought 20 SPOT tags for $5,000 apiece to help with Rumbold’s mercury study — the money for the tags came from the West Coast Inland Navigational District.

In 2010, the FGCU-Miami team SPOT tagged three great hammerhead, two bull and eight tiger sharks in the same area they fished last week.

“This is a pocket of biodiversity,” Miami doctoral student Austin Gallagher said. “There’s a lot of life. A lot of things for sharks to eat. It’s a great place to target sharks.”

Many shark populations are declining because of overfishing and habitat loss, and data about shark movements could help fisheries managers protect important shark breeding or feeding areas.

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“Sharks are difficult to study,” Gallagher said. “They’re large, and they move constantly. We like all species, but we’re looking for the biggest, baddest and most threatened.”

Following sharks also helps Rumbold determine how mercury moves through the food web offshore and in estuaries.

“I’m using mercury as a tracer to understand who’s eating who,” Rumbold said.

Mercury, especially its organic form, methylmercury, is bad business because it can impair neurological development in fetuses, infants and children.

Methylmercury moves through the food web by bioaccumulation: Almost all fish and shellfish contain traces of mercury, and when a predator eats prey that contains mercury, the prey’s mercury accumulates in the predator’s tissues.

When that predator is eaten, the new predator accumulates its mercury, and so on up the food web.

Sharks, of course, are at the center of the food web.

The most common way for humans to become exposed to methylmercury is by eating fish high on the food web — 40 states, including Florida, have issued mercury advisories for the consumption of fish.

Rumbold is also looking at mercury levels in sharks in the Ten Thousand Islands and reef fish in the Keys.

Mercury occurs naturally in the environment, but it is also introduced through human activities, including mining and burning coal and medical waste, and Rumbold’s data might ultimately be used to reduce mercury levels in the marine environment.

“Mercury’s been there forever,” he said. “All the mercury that’s ever been is still there, but we’re exacerbating it.

“The most important thing about any science is to understand a problem enough to make predictions, to tell what’s going to happen years out so we can make changes.”

But before the science can be done, sharks have to be caught.

On the first day aboard FGCU’s 25-foot research vessel last week, the scientists made five sets of 10 drum lines, and on the second day, they made 31/2 sets.

Despite such delectable shark snacks as amberjack, tuna, barracuda and king mackerel, the sharks weren’t biting.

Wasno speculated that red tide in the area had driven the sharks into deeper water.

“For the amount of effort we put in and the number of baits we had out there, a nurse shark or something should have come by,” he said. “But that’s the way science works. We’re always learning something.

“If we’d known red tide was going to be here, we would have aborted the event.”

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