Bob Care/Florida Keys News Bureau/AP

Staff members and volunteers from the Marine Mammal Conservancy care for four pilot whales Friday, May 6, 2011, in a temporary sea pen at Cudjoe Key, Fla. The four whales are part of a group of about 16 that stranded Thursday, May 5, off the lower Florida Keys. Three other whales are being cared for in the pen, two died and responders are endeavoring to secure the others in the sea pen.

CUDJOE KEY, Fla. — Rescuers workers treated and secured several pilot whales Friday that have been stranded off the lower Florida Keys.

Rescuers gathered eight of the stranded whales in a temporary sea pen, where veterinarians examined them and performed medical tests. One whale’s condition deteriorated Friday, and the animal had to be euthanized. The whales were constantly supported in the water by volunteers standing alongside them.

Marine mammal experts deemed the whales in the sea pen were in stable, but guarded condition.

“These guys are really weak now,” said Robert Lingenfelser, head of stranding operations for the Marine Mammal Conservancy. “They haven’t eaten in a while, so one of our jobs is to get them re-hydrated and ready for the next step of eating.”

The pilot whales were found stranded in multiple areas in shallow Gulf of Mexico waters and mangroves near Cudjoe Key.

Responders confirmed that 13 whales were dead. Necropsies are planned.

“We’re still in the process of rescuing the live marine mammals, trying to recover the dead ones so that we get good tissue samples for the scientists to investigate what’s going on here,” Lingenfelser said. “Right now our operations are geared toward recovery of all the animals out there, and they’re spread out all over the place.”

A few additional whales were spotted in Atlantic Ocean waters Friday, according to Karrie Carnes, communications manager for the Florida Keys National Marine Sanctuary. Teams of officials were recovering living whales and relocating them to the sea pen.

Officials said they were awaiting the arrival of additional personnel, transport vehicles and resources offered by other marine mammal organizations.

They hope to transfer surviving pilot whales to rehabilitation facilities sometime within the next few days. Alternatively, Carnes said, any healthy enough whale may be taken to deeper water for a release attempt as early as Saturday.