SEA BRIGHT -- A bid to rescue two dolphins from the Shrewsbury River yesterday ended with the death of one as marine mammal experts attempted to return them to the ocean or rehabilitate them to an aquarium.

Some 30 experts convened near the river early yesterday morning with plans to try to capture the two dolphins, a mother and her calf, who had been in the river for about two months.

But midway through the procedure it became clear the effort would not be successful.

The net capture of the two dolphins went smoothly. But about 30 minutes into the procedure, something went wrong. Experts said the older dolphin began going into respiratory arrest and died.

Her calf, believed to be about a year old, was then rushed with a State Police escort to the National Aquarium in Baltimore, where it will be rehabilitated.

Teri Frady, spokeswoman for the Washington, D.C.-based National Oceanic and Atmospheric Administration, who was at the rescue scene, said, "This is not the outcome we would have hoped for."

The pain of losing one of the mammals was evident, as experts slowly reviewed the chain of events. Although always conscious of the risks involved with such a rescue, Frady said that initially everything went so smoothly, the end result was unexpected.

By around 9 a.m., the two bottle-nose dolphins had been sighted near Oceanport. Soon after, both mammals were aboard a 26-foot-long vessel owned by NOAA on their way out of the sea.

They had been carefully placed on stretchers with the aid of divers, mammal handlers and marine biologists and lifted out of the water and into a special ambulance for animals. The plan was to have the dolphins transported about a mile to be released in the ocean, or transported to a rehabilitation center.

But the female dolphin had been breathing abnormally after she was captured.

Frady said that a blood test completed on the mother showed that she had been anemic and had an infection. The calf appeared to be in good health.

Dr. Richard Fernicola, a volunteer with the Marine Mammal Stranding Center in Brigantine, rushed both dolphins' blood work to Monmouth Medical Center, Long Branch, and later helped with the postmortem examination of the older dolphin.

Fernicola said the older dolphin's poor health may have been one of the reasons she remained in the river for almost two months. The dolphin may not have even been able to determine the change in water temperature due to her health, experts said.

About 8 feet, 7 seven inches long and about 300 pounds, the older dolphin's teeth appeared to be worn down, indicating she was older and her blubber content was about half of what it should have been to handle the river's water temperatures, according to Fernicola.

A full examination and more tests are needed to eventually determine the dolphin's cause of death, Frady said.

The dolphins had been in the river since September, and dipping water temperatures, coupled with a diminishing food supply, had some marine mammal experts calling for them to be rescued.

Both Frady and Fernicola pointed out that the outcome may have been worst if the National Fisheries Service in Gloucester, Mass. didn't give them an OK to go ahead with a rescue, since both mammals could have remained in the river and died.

Once rehabilitated, there is a chance the calf can still be brought to the ocean to continue its migration with another group of dolphins, experts said.

"It's always a judgment call," Frady said. "The alternative was bleak."