Among other things, the measurements helped determine the dosage of tetracycline that would be injected into the body cavity of the fish. This antibiotic leaves an identifiable reference mark in the shark's cartilagenous spine. If the shark is ever recaptured, the number of growth rings that have been formed since creating the marker will provide accurate information on its growth.
The scientists jabbed a tag into the nurse's dorsal fin—a long piece of monofilament with a tube attached containing a scroll of information for fishermen on what to do should they capture the shark. Then the team took a blood sample, rolling the creature on its belly, cutting through the hide to insert a needle, and drawing a syringeful out of the tail artery. The blood would later be analyzed on the basis of 12 different parameters. Of most interest to Gruber is the role hormones play in female shark reproduction.
Then the hook was pried as gently as possible from the shark's jaw, and the fish was sent on its way. The nurse took off with a great swish of its tail. It seemed more annoyed than damaged by the experience. That is not always the case.
A struggling 6½-foot lemon came up next, full of life when the scientists first approached. But by the time they got it mouth-up with dorsal fin down—which has a tranquilizing effect on sharks—most of its life seemed gone. "When you catch them, a few specimens seem to give up and just fade away," said Glavitza.
Manire held the lemon nose-down with one hand and worked vise-grip pliers back and forth, trying to get the hook out. "Give me a scalpel," he finally hollered. He cut the tissue around the barb until it popped out.
They let the shark go, but it sank limply to the bottom, landing on its back, its stark white belly showing up through the blue water from five feet below. We had observed the same scene several times in the past few months. But this time it was accompanied by a sick feeling of loss.
We were not alone in that feeling. Hastily, Manire jerked on his fins, mask and snorkle, and dived overboard. He flipped the dying fish over and began swimming it, propelling it forward to circulate the water through its open mouth and gills. We followed along in the boat, hoping it would come back to life and reclaim its place in nature.
At last the shark began to move, its caudal fin swishing back and forth. Finally, with a kick of its long graceful tail, it surged ahead under its own power. Manire swam behind for a moment, then popped up some distance away with a triumphant, "He's gone."
Now there was only open blue water, sea-grass meadows, and mangrove islands—and somewhere out there a tagged shark. A fearsome shadow of the deep.