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What’s Causing the Bottlenose Dolphin Deaths Along the Mid-Atlantic?

Since at least mid-July, NOAA Fisheries Stranding Network members from New York to Virginia have been responding to an alarming increase in bottlenose dolphin strandings, which are still occurring. In fact, bottlenose dolphin strandings in this area are over nine times the historical average for the months of July and August. So far, there have been 291 animals (as of August 26), compared to a historic mean of 26.  

On August 8, 2013, NOAA Fisheries officially declared this situation an “Unusual Mortality Event.” Since that time, dolphin strandings also have occurred in North Carolina. The Marine Mammal Stranding Network and NOAA Fisheries are collecting and analyzing samples to see if there is any relationship between all the strandings along the Atlantic seaboard.  It is possible that the mortality event may be expanding south (33 as of August 26, compared to historic mean of 4) as the dolphins begin their seasonal migration.

“We would not be able to respond to a stranding event of this magnitude if it were not for the tireless efforts and commitment of our partners in the Marine Mammal Stranding Network, who have been on the frontline,” said Dr. Teri Rowles, coordinator of NOAA’s Marine Mammal Health and Stranding Response Program. “Staff and volunteers from stranding organizations have been working around the clock to respond quickly to live or dead dolphins so we can investigate and figure out what may be causing these mortalities.” 

Numerous Stranding Network organizations along the east coast have been involved in the response, rescue, recovery and investigation aspects of this event, including: the Riverhead Foundation for Marine Research and Preservation in New York; the Marine Mammal Stranding Center in New Jersey; Department of Natural Resources in Delaware; the National Aquarium in Baltimore and Department of Natural Resources in Maryland; the Virginia Aquarium and Marine Science Center in Virginia; the Smithsonian’s National Museum of Natural History in Washington, D.C.; the University of North Carolina at Wilmington and Department of Environment and Natural Resources in North Carolina; The Marine Mammal Center in California; and the National Park Service.

What We Know So Far

Marine mammals, which include dolphins, whales and seals, strand for a variety of reasons.  While the investigation into this die-off continues, it appears to be affecting all age and sex classes of animals from the Coastal Migratory Stock of bottlenose dolphins. Strandings to date have included a few live animals with the majority comprised of dead animals with many already very decomposed.  A number of dolphins have been found with lesions on their skin, mouth, joints, or lungs.

After completing initial diagnostic tests on more than two dozen animals from all affected states and consulting with disease experts, we have determined that the likely primary cause of this event is a virus -- the cetacean morbillivirus, which is similar to measles in humans or canine distemper in dogs.

To date, 32 dolphins tested from all five states are either suspect or confirmed positive for morbillivirus. For 11 samples, genetic sequencing has confirmed this finding. Veterinary pathologists have also looked at eight animals and determined that detected changes in dolphin tissues are consistent with morbillivirus infection in all tissues analyzed.  Additional testing is being conducted on 27 other animals.  

A few tested animals were found to also have Brucella sp. bacteria lesions in their joints or brain tissue. Brucella is a type of bacteria that causes brucellosis and has been implicated in other marine mammal stranding cases in the Gulf of Mexico, Atlantic and Pacific coasts since 2010. Brucella has never been documented in humans after direct exposure to marine mammals, though there was a single case of occupational exposure in a laboratory worker who was collecting samples from an infected dolphin. Therefore, the risk of transmission of Brucella bacteria to animal care workers is likely low.

“We are very grateful to the scientists and technicians who are engaged in the ongoing testing that enabled us to make this preliminary determination and who will help us further as the investigation continues,” said Rowles. "The diagnostic labs assisting NOAA and the Stranding Network with the analytical aspect of this investigation include: the University of California, Davis; University of Florida; University of Georgia; and New Bolton Center, University of Pennsylvania."

Just over 25 years ago there was a similar outbreak of morbillivirus in the Coastal Migratory stock of bottlenose dolphins along the Mid-Atlantic during 1987-1988.

“About 50% of the coastal migratory bottlenose dolphin stock was affected, leading to the stock being classified as ‘Depleted’ under the Marine Mammal Protection Act,” said Rowles. “So we are obviously very concerned this particular stock may be reduced even further, and we are committed to doing everything we can to better understand how the virus is affecting the population.”

What is Morbillivirus?

Morbilliviruses are usually spread through the air or direct contact between animals, including between mothers and young. Cetacean morbillivirus affects the lungs, brain and immune system of dolphins causing illness and death. While this virus can easily spread among dolphin populations since the animals are highly social, it is not infectious to humans.

Morbilliviruses are naturally occurring pathogens in marine mammal populations, and because these viruses suppress the immune system, many animals ultimately die from secondary infections. Not all dolphins exposed to morbillivirus will die from these infections, but a large proportion may not survive.  

Unfortunately, there is no way to currently stop the spread of the virus. There are no vaccines or anti-viral medications available to administer to wild dolphin populations in an effective or practical manner.  However, what we can do is learn more about any other factors that could be making these animals more vulnerable to the spread of this disease and try to address and mitigate them to reduce additional stressors. Therefore, it is important that we continue our investigation.

What You Can Do to Help!

If members of the public find a live or dead stranded marine mammal, they should immediately call the local marine mammal stranding network which will send trained responders to evaluate the animal and take the next appropriate steps.

For additional information on how to help a stranded marine mammal, please see:

http://www.nero.noaa.gov/prot_res/stranding/HelpingStrandedMarineLife.pdf

http://sero.nmfs.noaa.gov/protected_resources/marine_mammal_health_and_stranding_response_program/documents/seus_stranding_brochure_final_2010.pdf

Next Steps

Further studies, in collaboration with several NOAA Fisheries laboratories and science centers, stranding network members, non-profit research organizations and academic partners will continue over the next several months as new animals are found or new evidence determines the direction of the investigation. These rigorous investigations may take several more months to complete. However, we will make every effort to make these data available to the public, as quickly as scientifically possible, on our UME website http://www.nmfs.noaa.gov/pr/health/mmume/midatldolphins2013.html

Click here for Audio from 8/26/13 media availability.