LEWES, Del. -- Juan Sabalones patted the back of Shark CT 90-4 and gently rubbed her smooth skin.
"I hope nobody catches her," said Mr. Sabalones, a senior aquarist at Baltimore's National Aquarium, bidding farewell to one of four sharks that were returned to the sea off Delaware's coast yesterday.
The creatures -- a sandbar shark and three sand tiger sharks -- were the first of the hundreds of fish to be moved as the aquarium prepares for a 15-month overhaul of the Atlantic Coral Reef and Open Ocean ring tanks.
The aquarium will remain open during the $12.7 million overhaul, with new exhibits and a laser animation show to compensate for the emptied ring tanks.
Over the next few weeks, aquarium staffers will be going fishing --indoors -- as they round up the remaining 10 sharks and hundreds of other species, transferring them within the aquarium or storing them elsewhere. Two sand tigers will go on loan to a Connecticut museum.
The sharks taken to Lewes, where the aquarium has a collection station at the University of Delaware's College of Marine Studies, enjoyed a homecoming to Atlantic waters after several years in captivity.
The year of their capture is part of the animal's identification code.
"90-4," Bruce Hecker said wistfully. "I remember catching her, on a rod and reel."
Mr. Hecker, the aquarium's curator of fishes, completed a National Marine Fisheries Service tag showing the female shark's 8-foot length and 201-pound weight (dripping wet, of course). She will wear the tag on a barb placed so that it won't get in her way.
The code also indicates scientific name -- the tiger shark's CT is for Carcharias taurus, the sandbar's CP for Carcharhinus plumbeus.
The keepers know the sharks by numbers and sight. Each has unique patterns of scrapes and color.
Preparations for the release began early in the day at the aquarium, where divers went into the "ray pool" to corner and catch the sandbar shark, about 22 pounds and believed to be no more than 4 years old.
The sand tigers, around 200 pounds and believed to be 20 to 30 years old, were herded one at a time through their tank into a back-room pool with a 1-ton hoist.
A team of three aquarists went into the pool and slipped a sling under the biggest shark -- 90-4 --and tried to keep her head in an interior pouch. She was not cooperating.
"Watch out. Her head's free," an onlooker said as the shark opened her mouth in what seemed to be a silent but very toothy snarl.
"Jaws," said another aquarium worker, clearly impressed by the business end of 90-4.
The sharks were wheeled out of the aquarium in custom-built boxes partly filled with water and equipped with a pump to keep oxygen bubbling through them.
They were driven to Lewes, with two sharks riding in the back of a panel truck, the other two in a van.
At the shore, the animals were transferred to a holding pool on the aquarium's 23-foot fishing boat and taken more than a mile off Cape Henlopen. After four boat trips, it was late afternoon before the last shark was freed.
Mr. Hecker said evidence suggests that the number of sharks in the mid-Atlantic region has declined and that freeing the animals is a gesture to the need for conservation.
The aquarium plans to replace the sandbar and sand tiger sharks with other species to diversify the exhibit when it reopens.
Mr. Hecker doubted that the free sharks would have much trouble adapting to open waters. having lived there before.
He said the sharks would not pose much danger to humans, since attacks are rare and usually are caused by some stupidity on the victim's part.
But the aquarium crew worried about the danger people pose to the sharks.
Mr. Hecker said he hoped the sharks would follow their instincts and head south to warmer waters so that the older sharks -- two males and the female -- might breed.