OCEAN CITY — A virus is blamed for the summer-long spike in the number of bottlenose dolphin deaths along the mid-Atlantic coast from New York to Virginia, including one involving a sick dolphin that beached itself in Ocean City yesterday as well as a dead dolphin that washed ashore this morning on 49th Street.
Since at least mid-July, NOAA Fisheries Stranding Network members, including the National Aquarium’s Marine Animal Rescue Program (MARP) and the Maryland Department of Natural Resources, have been responding to an alarming increase in bottlenose dolphin strandings and the trend has not abated. In fact, bottlenose dolphin strandings have increased ten-fold over the historic statistical average during July and August. Thus far this summer, there have been 291 cases of dead or dying dolphins recovered or rescued in the mid-Atlantic region compared to a historic mean of 26.
In early August, NOAA fisheries officials declared the situation an “unusual mortality event” and began conducting research, and in many cases, necropsies on the deceased dolphins. It now appears the trend is starting to spread as the dolphins begin their annual migration south. For example, there have been 33 cases reported off the coast of North Carolina in the last few weeks, compared to a historic average of four.
Relying on programs like MARP and the DNR in Maryland and similar agencies throughout the mid-Atlantic states, NOAA Fisheries have recovered many dead or dying dolphins and few live strandings and have begun to develop a possible cause for the massive die-off.
“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,” said Dr. Teri Rowles, coordinator of NOAA’s Marine Mammal Health and Stranding Response Team this week. “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.”
After completing initial diagnostic tests on more than two dozen animals from all of the affected states including Maryland and consulting with disease experts, NOAA has determined the likely primary cause of the unusual mortality event is a virus, more specifically a cetacean morbillvirus, which is characterized as similar to measles in humans, or canine distemper in dogs. Strandings to date have included a few live animals, although the majority has been dead dolphins, many of which have been severely decomposed. A large number of dolphins have been found with lesions on their skin, mouth, joints and lungs.
To date, 32 dolphins tested from all five states in the affected region, including Maryland, are either suspected or confirmed positive for moribillvirus. In 11 samples, genetic sequencing has confirmed the findings. Veterinary pathologists have also looked at eight animals and determined that detected changes in dolphin tissues are consistent with the morbillvirus infection. Additional testing is now being conducted on 27 other animals.
About 25 years ago, there was a similar outbreak of morbillvirus in the coastal migratory stock of bottlenose dolphins along the mid-Atlantic during 1987 and 1988. The apparent outbreak this summer has taken on similar characteristics.
“About 50 percent of the coastal migratory 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 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.”
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