The deadliest known outbreak of a measles-like virus in bottlenose dolphins has killed a record number of the marine mammals along the U.S. Atlantic coast in recent months, officials said Friday.
A total of 753 bottlenose dolphins have washed up from New York to Florida from July 1 until Nov. 3, according to the National Oceanic and Atmospheric Administration (NOAA).
The figure represents a 10-fold increase in the number of dolphins that would typically turn up dead along East Coast beaches, said Teri Rowles, program coordinator of the NOAA Fisheries Marine Mammal Health and Stranding Response Program.
“Historic averages for this same time frame, same geographic area, is only 74, so you get an idea of the scope,” she told reporters.
The cause of death is morbillivirus, a form of marine mammal measles that is similar to canine distemper and can cause pneumonia, suppressed immune function and brain infections that are usually fatal. The virus spreads among dolphins in close contact to one another.
The death toll is also higher than the 740-plus strandings in the last major Atlantic morbillivirus outbreak in 1987-1988. And they have come in a much shorter time period, leading officials to anticipate this event could get much worse.
“It is expected that the confirmed mortalities will be higher,” said Rowles. “If this plays out similar to the ’87-88 die-offs, we are less than halfway through that time frame.”
Rowles said efforts are underway to try to determine if the virus might have been introduced into wild bottlenose dolphins from another species, like humpback whales or pygmy sperm whales.
“There are still a lot of unanswered questions about that,” she told reporters.
Among bottlenose dolphins, immunity to the virus has been decreasing, particularly in the younger animals as time has gone by since the last outbreak 25 years ago.
“So we know we had a susceptible population, but just being susceptible alone is not how the outbreaks go,” she said. “We are trying to understand where this virus came from and how it got into the population in which it is now circulating.”
In the meantime, the process of dealing with all the dead carcasses has been “overwhelming,” particularly for local recovery teams, Rowles said.
The Virginia Aquarium alone has had to pick up and do necropsies on 333 animals in the space of just a few months, said Ann Pabst, co-director of the University of North Carolina Marine Mammal Stranding Program.
“You can imagine that it really does become an all-consuming sort of job,” she said.
“They have done heroically well in keeping up.”
Five percent of the dolphins have been found alive on the beaches, but died soon after, NOAA said. The virus has appeared to infect dolphins of all ages, from young to old.
But since the number of dolphins washing up on shore may not represent all of the creatures that are dying, it is difficult to estimate what proportion of the population is sick.
And without a way to vaccinate the wild population, there is little that officials can do but collect the carcasses and continue to study them.
While NOAA hasn’t determined a cause for the deaths, other scientists have speculated that mass die-offs like this one are becoming increasingly common as climate change causes water to warm, and human-produced pollution weakens dolphins’ immune systems.