When you look up from your book during your summer trip to the shore, nothing sparks the imagination like the quick, dark glitter of a curved dorsal fin dipping playfully through the surf, just beyond the breakers. With a flash of gray flukes and a white burst of breath, the dolphins speed by.
But this summer, the mid-Atlantic is teeming with reports of a threat local dolphins haven’t faced since the late 1980’s. According to the National Oceanic and Atmospheric Administration (NOAA) Fisheries, as of August 26th, bottlenose dolphin strandings have topped nine times the historical average, with a count of 333 dead dolphins from New York to North Carolina. That led NOAA, under a provision of the 1972 federal Marine Mammal Protection Act, to declare an Unusual Mortality Event (UME) for bottlenose dolphins in early July. This means losses significant enough to deplete certain dolphin populations over the next several years.
So far, Virginia has seen a peak in the strandings, with a total of 174. From July 1 to Aug 26, New Jersey had 71.
An answer at last
NOAA scientists and a raft of pathology and marine experts announced a definite cause for the die-off in an August 27 press conference.
“We are now calling this a morbillivirus outbreak that extends currently from New York to Virginia for confirmed cases,” said Dr. Teri Rowles, of the NOAA Fisheries Marine Mammal and Stranding Response Program. “Ninety-seven percent of animals tested so far are showing morbillivirus, suspect or confirmed through molecular techniques.”
What is morbillivirus?
According to NOAA, morbillivirus is actually a class of viruses that affect different species. For dogs, coyotes, wolves and seals, it’s canine distemper. For humans, make that the measles. While U.S. marine mammals are susceptible to four different strains of the virus, many of this summer’s dolphin victims had what’s known as cetacean morbillivirus.
Cetacean morbillivirus manifests in a few different ways, NOAA experts explained. It’s not always fatal, but many affected dolphins are thin and have breathing problems, including pneumonia. Necropsies often show lesions of the skin, mouth, lungs and brain. The illness also suppresses the dolphin’s immune system, so that secondary infections—sometimes fatal—set in. The vast majority of beached mobillivirus victims washed up on shore after they died in the water.
A danger to humans?
The virus spreads among the dolphins much like the flu spreads on land: through direct physical contact, as with a mother and calf, or through respiratory particles when the dolphins surface together to breathe.
Warnings that people should not approach dolphin corpses have some bystanders worried that the ocean epidemic poses a risk to humans. But Dr. Jerry Saliki, a pathologist from the University of Georgia, insisted humans can’t catch the dolphins’ sickness.
“In many parts of Africa and Asia, humans have been exposed the centuries over to morbillivirus, and there is no evidence that it infects humans,” he said. Rowles explained that warnings to stay away from affected dolphins have more to do the secondary viral, bacterial or fungal infections that these animals often succumb to, some of which are also dangerous to humans.
“For people who are not trained working with these animals, it’s much better to stay away from stranded animals, particularly if you have open wounds,” Rowles said.
Why are they dying now?
From summer of 1987 to spring of 1988, mid-Atlantic scientists observed another major dolphin UME that was also attributed to morbillivirus. Over 740 animals died from New Jersey to Florida in that outbreak.
NOAA experts theorize that in the 25 years since the last outbreak, mid-Atlantic dolphin populations have seen a decline in their natural immunity. The disease is always harbored in a few individuals, and it may even have jumped to the mid-Atlantic dolphins from other deep-sea mammal species. So the dolphins from New York to North Carolina, relatively disease-free for so long, were once more susceptible to the infection on a large scale.
“As this virus moves through the population, some will die [and] some will gain valuable exposure,” said Dr. Stephanie Venn-Watson of the National Marine Mammal Foundation. According to her, “decreased antibodies that took 25 years to occur,” and not pollutants or other environmental factors, account for the severity of the current outbreak.
How long will it last?
Similar to the way that the 1987-88 UME receded, NOAA predicts that this year’s dolphins, whose strandings have followed a very similar pattern, will also recover eventually. The outbreak is expected to spread further south, as dolphin groups migrate, before it tapers off in spring 2014.
“Exposed or re-exposed animals will no longer become sick or die or get stranded,” Saliki said of the epidemic’s eventual end.
“At this point there isn’t anything we can do to stop the virus,” Rowles said. “We don’t have a vaccine that could be easily deployed in a wild population of bottlenoses.”
For now, in an effort to better understand the virus and its effects, east coast scientists are racing to learn the extent of the outbreak, which populations it’s affecting, and to what extent. The complicated modeling will include scrutinizing the demographics of affected dolphins, comparing post-outbreak population surveys with pre-outbreak ones, and monitoring other stranded species for the illness. Understanding UMEs can offer important insights for larger questions of ocean health, and even human health.
New Jersey beachgoers who spot a stranded dolphin should call the Northeast’s marine mammal stranding network at 1-866-755-6622.