An unusually high number of bottlenose dolphins are dying off the east coast of the United States this summer, the deadliest period for the sea mammals since a virus killed off more than 700 in the late 1980s, U.S. federal officials said Thursday.
Researchers are investigating what may have killed the 124 dolphins found stranded in coastal areas in the Mid-Atlantic region since July — seven times the historic average, National Oceanic and Atmospheric Administration officials said. All but seven of the dolphins were already dead when they were discovered, and each of those eventually died or had to be euthanized.
It isn't clear whether an infectious disease is causing the deaths; scientists plan to test blood and tissue for viruses, bacteria, fungi and biotoxins, among other things. But humans and marine mammals do share common pathogens, and anyone who finds a dead dolphin is being urged to stay away from it and contact authorities.
'Unusual mortality event'
The discoveries have led the federal agency to declare an unusual mortality event for bottlenose dolphins, a significant designation that Congress created in the wake of the in the 1989 Exxon Valdez oil spill and previous dolphin kill-off.
The declaration means scientists will have access to additional research funding. That investigation and analysis by teams of national and international experts could take months or even years to finalize, and officials say there is likely little they can do to stop the deaths unless the root cause is ultimately blamed on humans. And determining a cause is difficult: Of the 60 unusual mortality events declared since 1991, causes have been determined for only 29 of them.
Among dolphins, other strandings have also been caused by trauma, starvation, algal blooms and pollution.
At the top of the suspect list for the deaths is the same disease that led to 740 dolphins dying between New Jersey and Florida in 1987 and 1988, a morbillivirus infection. Morbillivirus is found in a broad range of marine mammals like seals, and its symptoms often involve lesions appearing in the lungs and central nervous tissues. Many of the dolphins have washed up badly decomposed, and lesions have been found in some of them.
One of the washed-up dolphins has already preliminarily tested positive for morbillivirus, but officials say it is too early to tell if that is the culprit for the other deaths. So far, necropsies haven't revealed a unifying cause. The morbillivirus passes from dolphin to dolphin, and bottlenose dolphins are typically found in groups of two to 15.
"We're not saying that this is a morbillivirus outbreak," Teri Rowles, NOAA's National Marine Mammal Stranding Coordinator, said in a conference call with reporters. "But because of the size of it right now, everybody's making that link at this point. But that is not a confirmed diagnosis or cause of this event at this point."
Officials say the spike in strandings began in early July, with dead dolphins reported in New York, New Jersey, Delaware, Maryland and Virginia. There are two different stocks of dolphins that populate that region, with the northern stock having between 7,000 and 9,000 dolphins, while the southern stock has between 9,900 to 12,000 dolphins, according to federal estimates. Rowles said the population is too large for there to be a plan to vaccinate or otherwise treat the animals.
Virginia has experienced the largest increase in dolphin strandings this year, with most occurring along heavily populated beaches at the mouth of the Chesapeake Bay. Officials say the number of dolphins that have died is likely greater than the number reported, with many more likely dying at sea and not washing up.