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(News-Press.com) - A rainbow's end touched the Gulf of Mexico a few miles offshore at 7:30 a.m. Wednesday as three FGCU scientists approached Redfish Pass aboard a 22-foot Tidewater center console boat.

Their mission was to fish northern Pine Island Sound for mangrove snapper, snook, spotted seatrout and redfish for an ongoing project looking at how mercury moves through the marine food web.

Principal investigator Darren Rumbold and David Fugate, associate professor of marine science, thought the rainbow was a good sign, but Bob Wasno wasn't sure.

"We want God to be more explicit," said Wasno, education and resource coordinator at FGCU's Vester Field Station. "We want a neon arrow pointing at the fish."

The chemical element mercury occurs naturally in air, soil and water; human activities such as burning municipal waste and burning coal in power plants can increase elemental mercury in the environment.

Natural chemical reactions can turn elemental mercury into oxidized mercury; bacteria can then convert oxidized mercury into methylmercury.

Methylmercury is the bad form: It's a neurotoxin that accumulates in animal tissue, and it bioaccumulates, or works its way through the food web.

If, for example, a pinfish eats shrimp that have methylmercury in their tissues, that methylmercury accumulates in the pinfish; a snook that eats methylmercury-laced pinfish absorbs all their mercury, and so on through the food web, eventually putting people in danger of mercury poisoning.

The Florida Department of Health lists 60 marine and estuarine bony fish species and all shark species for limited consumption.

Rumbold, a professor of marine science, has already completed a study and published a paper on mercury in sharks caught in the Gulf and is now investigating estuarine food webs.

In addition to Wednesday's target species in Pine Island Sound, the project is targeting sheepshead, menhaden, pinfish and invertebrates.

The yearlong study, which has six months to go, includes the Caloosahatchee Riverand Shark River in Everglades National Park.

"We're interested in mercury because of its health threats," Rumbold said. "Mercury is stored in things we like to eat: filets of fish. We should be eating fish. We need to be eating fish. We just need to pick the right fish."

Rumbold's project will ultimately help people pick the right fish.

"Looking at the whole food web, we can develop models to predict how mercury is transferred to the next level," Rumbold said. "We've got to understand the whole picture to make management decisions."

To test fish for mercury, of course, fish must be caught (the more, the better), but the target species weren't cooperating Wednesday: Fishing the outgoing tide on both sides of Redfish Pass for three hours, the scientists caught four mangrove snapper, and various non-target species, including a 12-inch pompano.

Driving the boat, Army veteran Wasno exhorted the fishermen: "You guys need to focus. Have a positive attitude. Be the fish. If you don't get your minds right, I'm going to take you up on the beach and make you do push-ups."

As the tide continued to fall, the scientists moved to a nearby grass flat known to hold redfish at low water — nothing.

At 1 p.m., Team Rumbold returned to the staging point, the Tarpon Lodge on Pine Island, to weigh and measure the snapper, document stomach contents and take a tissue sample from each for analysis; the filets were put on ice for future consumption.

After lunch at Cabbage Key, the scientists drifted the incoming tide at Captiva Pass(more nothing) and a grass flat east of Cayo Costa's Pejuan Point (and still more nothing).

Throughout the day, squalls popped in every direction, and on several occasions the scientists were caught in the rain. According to the Sanibel-Captiva Conservation Foundation's weather station at Redfish Pass, the wind while the scientists were on the water was westerly, blowing in the teens with gusts in the 20s.

Late in the afternoon, a particularly ugly thunderstorm moved in from the Gulf, and the scientists decided the prudent action would be to get off the water.

Over cold beer, black beans and rice and fresh mangrove snapper and pompano that night, the scientists evaluated the day's research.

"There are good days and bad days," Fugate said. "This was closer to a bad day."

Wasno disagreed.

"We persevered, so I'd put it in the win column," he said. "But we did have plenty of rain and lightning and not many fish. In the future, we should follow the rainbow."

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