A virus that killed more than 750 dolphins in the late 1980s is the likely cause of death for 291 dolphins between New York and North Carolina since July 1, officials with the National Oceanic and Atmospheric Administration said Tuesday.
Morbillivirus, which is similar to measles and canine distemper, has been either suspected or confirmed in all 27 of the animals tested, including four from New Jersey, said Teri Rawles, director NOAA’s marine mammal stranding program. Rawles, speaking on a conference call with reporters Tuesday, also said that researchers expect that the outbreak will travel down the Atlantic coast as migratory populations move into warmer waters this fall and winter.
“We don’t have a lot of insight into when it will stop,” Rawles said. “We’re expecting that, if indeed this plays out the way the die-offs occurred (in 1987) that we are looking at mortalities being higher and mortalities spreading southward and likely continuing into the spring of 2014.”
Since July 1, 74 dolphins have washed up dead or dying in New Jersey, the second highest number of any state dealing with the outbreak. The Marine Mammal Stranding Center in Brigantine said four dolphins washed up Sunday alone.
Virginia, Rawles said, is the hot zone with 174 dead dolphins as of Monday. The outbreak is likely stretching into North Carolina, with 42 dolphins reported as of Monday.
A total of 333 dolphins between New York and North Carolina so far have died since July 1, and 488 have died since Jan. 1.
The 1987 outbreak began in June of that year and lasted until May 1988. Nearly 750 dolphins were killed, but that number does not include animals that did not wash ashore. Additionally, there were no stranding response networks at the time, and other animals that did wash up may not have been collected.
Scientists who studied the 1987 morbillivirus outbreak estimated that as much as 50 percent of the nearshore population died, but Lance Garrison, of NOAA fisheries, said later research has questioned that figure.
However, Garrison said, the die-off was so significant that the loss resulted in the federal government listing the Atlantic Bottlenose Dolphin along the East Coast as a “depleted stock.”
“With such a high number (of deaths), there is the concern of a significant population impact,” Garrison said. How big that impact will be may not be known until after the outbreak ends and scientists can analyze an array of data relating to populations.
Researchers said they suspect the trigger for the virus outbreak is the number of animals that have not developed a natural immunity to the disease has reached a tipping point. Once the virus was introduced, it spread quickly.
“The preliminary hypothesis is the East Coast dolphins simply don’t have the immune response to fight off this virus,” said Stephanie Venn-Watson, of the National Marine Mammal Foundation. “Reaching that tipping point is believed to be the leading cause as to why this is so severe.”
And even though scientists think the cause of the die-off is a virus, there is no way for them to be able to stop it, Rawles said.
“We don’t do vaccinations in wild populations of dolphins, so we rely on their natural immunity,” she said. “What we know about the East Coast population through other studies is that many of the dolphins younger than 26 years old have limited to no immunity to this virus.”
Rawles said the virus likely will have to run its course until the most susceptible animals have either died or have developed a natural immunity after being sick. Not all infected dolphins are dying, but researchers do not yet know how lethal the virus is.
Dolphin morbillivirus usually is spread by breathing in infected particles or through direct contact with an infected dolphin. The virus initially causes a suppressed immune system in the infected dolphins. Many of the animals coming in appear to have been ill for some time, said Margaret Lynott, with the Virginia Aquarium and Marine Science Center. Some of the animals have mouth lesions, brain lesions or pneumonia.
However, Lynott said, animals of all ages, both male and female, are dying and there is no pattern for which dolphins are affected more than others.
Researchers are looking into how any sort of environmental stressors, such as manmade pollution, could be factoring into how the illness will run its course, Rawles said. Certain types of chemicals, such as PCBs and mercury, can cause dolphin immune systems to weaken.
While scientists said there is very little chance the virus could make humans sick, they warn anyone who comes across a stranded dolphin not to touch the animal because of other bacteria that could affect people.
To report a stranded dolphin, contact the Marine Mammal Stranding Center’s 24-hour hotline at 609-266-0538.
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