The upside-down baby shark pinned under David McElroy's arm wriggled madly but stopped when the researcher slid a 10-inch-long piece of plastic pipe into its mouth and waaay down its throat.

Slowly, McElroy withdrew the pipe. Out spewed the slimy contents of the shark's tummy -- along with the tip of the glistening red stomach itself! (Sharks do this trick naturally. It's called everting and it's how they expel foreign objects.)

Avoiding the two-foot-long creature's pointy teeth, McElroy tucked in the stomach and released the baby shark back into the shallow waters of Delaware Bay.

"Aha!" he said, leaning over the bucket of shark barf and pulling up a drippy chunk of fish skin the size of a potato chip. "It's a kind of flatfish called a hogchoker. . . . Very good!"

On a summer morning, McElroy and Camilla "Cami" McCandless, researchers from the University of Rhode Island, were about 11/2 miles offshore, near Lewes, Delaware, studying the sandbar shark (Carcharhinus plumbeus) for the National Marine Fisheries Service. The agency tracks fish species to make sure their numbers are not falling too low, possibly due to overfishing. If a species is in trouble, officials can further limit how many can be caught.

Where the Sharks Are

The Delaware and Chesapeake bays are the most important nursery grounds for sandbar sharks in the northwest Atlantic Ocean. Adult females come to the deeper bay waters to have their babies. Most of the young sharks seem to spend their winters in the warmer waters off North Carolina and South Carolina, then return each summer to the bay waters where they were born, McCandless said.

After about six years, sharks may range as far north as Massachusetts, and south to the Gulf of Mexico.

The fisheries service has been coming to Delaware Bay since 1995 to study young sandbar sharks, which are caught (with nets or long fishing lines), tagged, measured, weighed, examined and released. Comparing the results over time lets officials know how the species is doing and how to protect it. Overfishing has pushed many species of shark, including the sandbar, toward extinction. Sharks are mostly caught for food; their fins are delicacies in many Asian countries.

Intense fishing in the 1980s shrank the local sandbar shark population to less than 20 percent of what it was in the 1970s. In 1992 the government tightened the rules so that fewer sharks would be caught. Officials also banned finning (catching sharks just to slice off their fins).

Today, the sandbar population is about half what it was in the 1970s. The government says the population needs more rebuilding, but fishermen and some scientists disagree over how much.

Shark Quest

The researchers began their day by putting chunks of mackerel on barbless hooks that dangle from a 1,000-foot line. After 30 minutes, they started reeling in the catch.

McCandless lifted a silver-gray shark, still snapping and squirming, into the boat and stretched it out on the measuring table.

"Okay, we've got a male, at least a year old," she said, basing her guess on the animal's size and faint belly-button scar.

She weighed the shark and took other measurements -- nose to tail, it was nearly 30 inches -- then injected it with tetracycline. The antibiotic stains the shark's backbone like a tree ring, so if the animal is ever dissected, scientists will know how much time has passed.

McCandless made a small opening in the shark's dorsal fin and snapped on a blue identification tag. Then she clipped off a tiny piece of fin to keep as a DNA sample. Finally, she handed the shark over to McElroy for everting.

An Emptied Stomach

The researchers clearly love their subjects. "Once you work with sharks . . . it's amazing," McElroy said.

"First, I'm going to give this one a little drink," he said, dipping the shark in the water to give it more oxygen.

Sometimes, after emptying a shark's stomach, McElroy throws the mackerel bait back in. "He feels guilty for stealing their meal," McCandless explained with a chuckle.

Learning what sharks eat gives scientists a better picture of how they fit into the ecosystem. Biologists want to know what each animal eats (and what eats it) so they can protect all links in the food chain. Sandbar sharks, for instance, like to eat crabs and certain little fishes. So if those critters started disappearing, scientists know that sharks would be affected.

Most of the sharks McElroy examined on this day had little in their tummies, just a tiny crab knuckle or a bit of butterfish.

By the end of the session, the two researchers had examined 23 sharks, the largest almost 30 inches long. (Adults can be six or seven feet, but the longest they've caught in Delaware Bay was a five-footer.)

As with any fish story, this one includes the tale of "the one that got away." Near the end of their fishing line, the researchers spotted a large fin on the port side.

"Wow, a big juvenile," McElroy said. "I was hoping we'd see one."

He pulled the line and, sure enough, it seemed to pull back -- hard. Or maybe it just snagged on something. McElroy pulled and pulled, but when the line finally popped loose it came up empty. All it held were a few bent hooks.

-- Fern Shen

Researchers

catch, measure

and tag

sandbar sharks

in Delaware Bay . . .. . . then remove the contents of their stomachs to see where the sharks fit in the ecosystem.