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Sharks are more spread out in the winter waters of the Gulf of Mexico, so the 24-hour expedition was a gamble.

The team of scientists set out on a boat with four satellite transmitter tags in search of silky and dusky sharks. Once attached, the tags would log the sharks' location, the water temperature and depth every minute, and then pop off weeks or months later and transmit the data to a satellite. The data would become a virtual map of shark travels, a way to "swim" beside them from a lab chair.

Shark life is a mystery to biologists, so the satellite tags are a new and welcome technology. Silky and dusky sharks are being overfished. Shark meat is worthless, but their fins fetch high dollar prices as an aphrodisiac and the base for shark fin soup. Understanding their travel patterns will help protect them.

"If it goes unchecked, we're going to lose the species," said Eric Hoffmayer, a shark biologist at the University of Southern Mississippi Gulf Coast Research Lab. Hoffmayer led the expedition, about 70 miles due south into deep water sparsely peppered with oil and natural gas rigs and the occasional deep sea fishing boat.

Sharks are at the top of the marine food chain. As they decline, their prey becomes more abundant. The abundant prey then decimates its food source, often shrimp, crabs and other seafood at the base of the chain.

The 97-foot R/V Tommy Munro glided all night, until about 5 a.m., when it hit some rough seas. Some of the team suffered seasickness. About 7 a.m. near an oil rig, researchers and crew set out the first long line. It held 100 hooks evenly spaced, tied to buoys to keep it afloat. Left to "soak," for an hour, the line drew nothing.

"That's why they call it fishing, not catching," said William Driggers, a scientist with the National Oceanic and Atmospheric Administration who works with Hoffmayer on shark projects. The identification tags will only show where the shark ends up. The researchers won't know what it did to get from point A to point B.

The team decided to move away from the oil rig and try again. Another long line floated out. Lunchtime crept up, but the researchers kept on. The first catch flopped around on the deck before being caught and unhooked. A fisheries biology student, Kristen Kelly, measured the silky shark with another team member. It was too small for a satellite tag, but OK for a regular tag. A few more silky sharks came up, also too small for satellite tags.

The morning's catch was not what was expected, but "better than zero? Yeah," said Kelly. After some discussion, the boat backtracked onto a third spot, rumored to be a good one with big sharks.

The third line went out in the setting sun, this time, weighted to fall to the ocean floor. Perhaps they would catch something feeding along the bottom. If a shark is too small, there is the danger that they will sense the weight of the satellite tag, altering their natural behavior and making the data useless, said Hoffmayer.

As night fell, the boat went over the line and snagged it in a rudder. The team worked amid shouts to free it, rather than leave it behind. One hundred ghost hooks, baited, could catch and kill a bunch of fish. In the final draw, some sharpnose sharks came up, along with a ray. Everything was tagged and thrown back to sea.

At 7:30 p.m., the boat headed back to its dock in Biloxi, more than six hours away. Even though the team didn't get what they came for, they learned something new. Finding all the babies near the rig indicates it could be a nursery, said Hoffmayer. Not all oil rigs support fledgling sharks, he said.

And even though they didn't deploy the $3,500 satellite tags, they want to, and soon. They have been trying for several months.

"Getting a satellite tag on a shark? You'll see people jumping up and down. It's a very rare event," said Driggers.