BRIGANTINE, N.J. (CBS DC/AP) — Once upon a time, he was known as Capt. Bob, the man who trained the dolphins and seals to perform for crowds in Atlantic City.

But as he got to know the dolphins, Bob Schoelkopf renounced keeping them in captivity and devoted the rest of his life to rescuing stranded marine mammals.

Now the man who once prodded dolphins to jump and wave their fins for crowds is part of a broad scientific effort to determine why dolphins are dying by the hundreds.

“It’s worst when you get a female come ashore and she’s lactating and you see the milk come out onto the stretcher,” said Schoelkopf, co-director of the Marine Mammal Stranding Center. “That means there’s a baby out there swimming around without a mother. That baby is going to become shark bait.”

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So far this summer, there have been about 230 dolphin deaths along the East Coast, prompting the National Oceanic and Atmospheric Administration to declare an unusual mortality event. That clears the way for an intensive scientific inquiry into what is causing the deaths.

No definitive conclusions have been reached, but many suspect the morbilli virus. The naturally occurring virus was ultimately blamed for the last major dolphin die-off, in 1987, when 740 dolphins died.

Marine biologist Kim Durham told CBS News that this type of virus resembles measles.

“When we were doing examinations, we would find they were very skinny animals,” Durham said. “They were compromised animals. Some of them had skin lesions — they were just very sick individuals.”

Durham added that the dolphins could be spreading the virus among themselves because of skin contact.

This year, several of the dolphins that washed ashore in New Jersey have tested positive for the virus.

The waves of dead dolphins started appearing in New Jersey in early July, and it hasn’t let up. Wednesday morning, the stranding center got a call about a dead dolphin that washed ashore in Sea Bright, the 62nd in New Jersey this year. But it was too badly decomposed and chewed up by sharks to warrant taking it for a necropsy at a veterinary center near Kennett Square, Pa., a four-hour round trip that’s exhausting volunteers.

Two hours later, another dead dolphin, No. 63, washed up in Spring Lake.

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One recent day in New Jersey, a dolphin came ashore at 1 a.m., was euthanized at 3 a.m., and staff had just gotten home into their beds when another dolphin washed ashore at 6 a.m.

Schoelkopf has been doing this for decades. A Vietnam veteran whose duty included underwater operations, he was injured during the war and sent to Philadelphia Naval Hospital. His diving experience allowed him to get a job at an aquarium, where he cleaned the underwater glass of the dolphin tanks.

One night, he was scrubbing away when he felt something nudge him from behind. It was a dolphin that had gotten out of its holding tank, one of several that had learned how to open the gate, swim out and then return after a while and snap the latch closed again.

“No one had any idea they were swimming out and playing around each night,” he said.

It changed his life.

“I didn’t want to work with captive dolphins anymore,” he said. “It wasn’t right for them to do 13 shows a day and never see sunlight.”

He founded the stranding center and has earned a national reputation for rescuing beached or distressed sea creatures.

He is well aware of the emotional effect sick or dead dolphins can have on people.

“Animals die all the time at sea, but people don’t see it,” he said. “They get upset when they do see it. They’re looking at Flipper.”

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