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Scientists use tags to follow lemon sharks

JUPITER — Shark scientist Steve Kessel was looking for the piscatorial equivalent of a needle in a haystack or a four-leaf clover in a meadow during a fishing expedition off Jupiter on March 6.

Kessel, a researcher from Cardiff University in Wales, and his assistants were fishing for a pregnant lemon shark into which they could insert a satellite tag. Under the direction of commercial fisherman Mike Newman, captain of the Dykoke, the crew deployed four large buoys holding stout fishing lines baited with bonito slabs on circle hooks.

They waited anxiously, hoping one of their study subjects would come along to help answer a question that has bugged shark scientists for decades: Where do lemons go to give birth to their young?

"We think they're pupping up in Georgia and South Carolina because we've shown through telemetry data the sharks move north in the summer months," Kessel said. "But we have yet to prove this."

Sometime around 8 p.m., one of the buoys began moving erratically. Newman motored the Dykoke closer so that research assistants could pull in the line and ease whatever was attached to it onto the deck.

After a brief struggle, a female lemon a little more than 8 feet long with a distended belly was lying quietly on board with a wooden paddle inserted between her jaws like a baby pacifier. A wet rag was thrown over her eyes to help calm her, and a hose pumped seawater into her mouth to avoid respiratory distress.

The scientists drew blood, recorded the animal's length and girth, took a tiny piece of fin for a DNA sample and inserted a small tag beneath the skin that can be read by a handheld electronic scanner. Then they added an external acoustic transmitter tag and produced a battery-operated drill to secure the SPOT tag to the dorsal fin. Every time the fin breaks the surface, the tag will beam its location to a satellite, with the data downloaded onto Kessel's computer.

The SPOT tag is different from a popup satellite tag in that it records only the shark's location — not depth or water quality or temperature. The acoustic transmitter tag pings to an array of 300 underwater listening posts installed by a host of research groups stretching from Florida to the Carolinas.

The female was one of more than 40 lemon sharks tagged this winter off Jupiter by Kessel's group. They also inserted tags in three bull sharks, one Caribbean reef shark, four nurse sharks and two hammerheads. Nearly 250 sharks of various species have been caught by the researchers since 2006. Only two lemons have the SPOT tags; the scientists are hoping for one more pregnant female to tag before the sharks leave the area this spring.

The lemon sharks that flock to Jupiter each winter are important study subjects because they are scientists' best hope of learning about the species.

First observed in 2001, large males and females gather by the score near wrecks and reefs, lying quietly on the bottom by day and foraging for food by night. Tagging data revealed the animals that showed up in Jupiter "blasted out of there" in April and headed to the Carolinas.

Scientists use tags to follow lemon sharks 04/02/11 [Last modified: Saturday, April 2, 2011 11:05pm]

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