CONSERVATION

Scientists studying why lemon sharks aren’t in South Florida this winter

 

Scientists are trying to learn why lemon sharks aren’t in South Florida waters this winter and what that might mean.

scocking@miamiherald.com

Sheryl Crow’s Grammy-winning song, “All I wanna do is have some fun ...” played ironically on the sound system as shark scientist Steve Kessel and four field technicians lassoed a nine-foot male hammerhead shark splashing and writhing in the water beside their 26-foot boat.

“Feisty. It’s a good sign,” Kessel remarked as he struggled to take a DNA sample from his unwilling study subject.

Just then, colleagues in another boat tried to raise Kessel on VHF radio.

“Tell them we’re indisposed right now,” the Englishman directed colleague Joanne Fraser, the boat’s owner.

With Fraser grasping one side of the shark’s protruding head and Jill Brooks, Lorena De la Garza and Abby Nease securing it with a tail lasso and for good measure — a rope around its pectoral fin, Kessel was able to perform quick surgery, leaning over the gunwales and inserting a small acoustic transmitter next to the pelvic fin. The post-doctoral fellow at the University of Windsor in Canada also stuck a small visible streamer dart tag behind its large dorsal fin.

As he worked, Fraser kept a firm grip on the “hammer.”

“I never thought I’d be staring a hammerhead in the eyeball,” she said, almost casually.

Within a few minutes, the work-up was completed, and the researchers slipped the ropes from around the shark. It quickly swam away, no doubt eager to shake off its ordeal.

It was the second hammerhead capture of the day near the wreck of the Zion Train, 85 feet deep off Jupiter. The first — an eight-foot female — had been caught on buoy gear baited with a barracuda carcass less than an hour earlier. Neither shark was what Kessel was looking for, but he decided to put transmitters on the two, anyway, to assist colleagues from other universities and fisheries management agencies studying hammerheads.

What Kessel really wanted were some lemon sharks to implant with transmitters. First discovered resting in groups of up to 150 around the wrecks and natural reefs in the area during winter months more than a decade ago, the lemons so far this winter have been absent. Kessel and project leader Samuel “Doc” Gruber, professor emeritus at University of Miami’s Rosenstiel School, believe higher-than-normal water temperatures and overfishing are to blame. Since 2007, the scientists have implanted 180 lemon sharks caught in the Jupiter area with acoustic tags that have pinged underwater receivers along the Florida coast to the Dry Tortugas, east to the Bahamas and north to the Carolinas. So far this season, 13 lemons have been detected off Cape Canaveral, but none in Jupiter.

Gruber said it’s important to gain a complete understanding of the animals’ movements and life histories.

“The aggregation is the focus of this study,” he said. “It makes these sharks like snapper and Goliath grouper — highly vulnerable to overfishing,” he said.

Gruber, Kessel, and other shark conservationists successfully lobbied the Florida Fish and Wildlife Conservation Commission to ban the harvest of lemon sharks in state waters — out to three miles from shore in the Atlantic — in 2010. Since then, the FWC also has prohibited taking tiger sharks and three species of hammerheads. The Bahamas recently banned all commercial shark fishing in its waters. But sharks still can be caught commercially in U.S. federal waters under a management system of seasons and quotas.

In order to convince NOAA Fisheries, which manages sharks in U.S. waters, to stop the harvest of lemons, hammerheads, bulls, and others, Gruber and Kessel want to leave no doubt about exactly what the animals are doing in Jupiter — particularly the lemons, since so much information already has been collected about them. Gruber has secured grant money to expand his grid of acoustical receivers around the MG 111 — a 60-foot deep artificial reef favored by the sharks as sort of a winter spa. With monitors spaced within 1,100 yards of one another, it would be hard for a tagged lemon to escape detection, and its movements could be determined more precisely.

Perhaps those findings will convince the feds of the need for conservation, Gruber said.

“It’s going to take somebody at NOAA to say, ‘These aggregations are real and have to be protected,’ ” he said.

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