A massive string of dead dolphins along the East Coast is most likely due to cetacean morbillivirus, a marine strain of a virus similar to measles, according to the National Oceanic and Atmospheric Administration.
At least 333 bottlenose dolphins have been found dead from New York to North Carolina, officials said during a Tuesday press conference. The strandings peak in Virginia, where 174 carcasses have washed ashore. The agency declared the die-off an "unusual mortality event" earlier this month.
Looking at a chart of past years, death rates are nine-times higher than usual.
A die-off this large hasn't happened for more than 25 years -- between the summer of 1987 and the spring of 1988, more than 700 bottlenose dolphins washed up along the coast. NOAA officials say they don't know when the strandings will stop, but the similarities between the events could mean they likely won't end until next spring.
Although morbillivirus is similar to measles in humans, animals affected by the outbreak aren't vaccinated in the same way we are, according to Dr. Stephanie Venn-Watson, director of translational medicine and research at the National Marine Mammal Foundation.
"East Coast animals simply don't have the immune response to effectively fight off this virus," she said.
To report a live or dead stranded dolphin, contact your local marine mammal stranding network.