A virus has killed more than 1,000 migratory bottlenose dolphins up and down the U.S. East Coast in 2013, a marine biologist with the National Oceanic and Atmospheric Administration said.
"It is having a significant impact and that is something we're monitoring closely," NOAA's Erin Fougeres said.
The 2013 death toll has already surpassed that of the most recent major outbreak of the measles-like virus in 1987-1988, when 740 dolphins died.
And the actual number of fatalities this year may be even higher, as the bodies of dolphins that died farther out to sea are less likely to be found.
"The last occurrence of this was about 25 years ago and the animals that survived that would have natural antibodies. But as those animals slowly die out and new animals are not exposed, they they not have that immunity," Fougeres said.
At the same time, she acknowledged that NOAA is also considering possible impacts from pollution or global warming.
"There could be underlying causes that made them more susceptible this year versus other years," Fougeres said. EFE