A silent, mysterious plague is claiming the lives of scores of bottlenose dolphins off the mid-Atlantic coast. Over July and August so far, 228 dead or dying dolphins have washed up on beaches from New Jersey to Virginia, and the numbers continue to climb. 

The dead include adult animals and calves, males and females. Sometimes, the animals that wash ashore are dead for days. Others arrive on their last breath. None have survived.

The National Oceanic and Atmospheric Administration has formally classified the mass deaths as an "Unusual Mortality Event." The daily arrival of dead dolphins is an ominous sign of a larger, ailing coastal ecosystem, researchers say. It could even signal the return of a deadly sickness that raged for 10 months in the late 1980s, and felled more than 700 bottlenoses before the carnage ended.

"We started getting really alarmed by July 25, when we started getting more than one animal per day. That was the tipping point," Susan Barco, a researcher at the Virginia Aquarium Marine Mammal Center, told NBC News.

August usually brings about seven strandings to the Virginia shores, but this month, with two weeks to go, Barco has already counted 75 dead dolphins. And calls about new strandings are flooding in daily. "There are days when we cannot get off the phone," she said. "Everyone loves dolphins ... they're certainly concerned."

Of the world's 600,000 dolphins, up to 22,800 coastal migrators — some heading south, to the Carolinas for the winter, and others heading north — are expected to pass through the mid-Atlantic in the summer and fall. "We are worried that ... the elevated strandings will not stop until the dolphins leave our area," Barco said. 

Researchers across the U.S. have rallied to support the investigation, at labs, at stranding sites, and at other remote locations. If volunteers find a recently dead animal — a carcass in good shape — they drive them to the aquarium lab facility. There, a team of three or four researchers works for about seven hours collecting swabs, tissue samples, body fluids — material that can be probed for viral or bacterial pathogens. Genetic tests are also on the to-do list. 

From whole animals, Barco has recorded respiratory infections, joint infections, skin and mouth lesions. Some animals appear emaciated, as if they suddenly went off their food. But the real killer — likely a bacteria or virus of some kind — is still at large. 

Nidhi SubbaramanNBC News

This is the latest news, and sadly condition :( #saveDolphin