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Deceased male dolphin on Ocean View Beach in Norfolk, Va. on Thursday, Aug. 1, 2013.

Trained responders examine a dead male dolphin on Ocean View Beach in Norfolk, Virginia, on August 1.

Photograph by Dorothy Edwards, The Virginian-Pilot/AP

Christine Dell'Amore

National Geographic News

Published August 7, 2013

Bottlenose dolphins are washing up dead in unusually high numbers along the U.S. East Coast this summer—a "very alarming" situation that has experts scrambling to decipher the cause.

Nearly 120 corpses have washed ashore in coastal states from New York to Virginia in July and the first week of August, which is much higher than the normal number of strandings attributed to natural deaths. Virginia has had the highest mortality, with 64 animals found during that period.

One of the dolphins tested positive for morbillivirus, a measles-like, airborne virus that's often fatal in dolphins.

A morbillivirus epidemic hit East Coast bottlenose dolphins in 1987 and 1988, wiping out at least 900 animals and striking a major blow to that population of migratory dolphins.

"Because of the sheer number of animals [dying] over multiple states, people are very concerned that this might be a repeat," said Trevor Spradlin, a marine mammal biologist for the U.S. National Oceanic and Atmospheric Administration's (NOAA) National Marine Fisheries Service.

Several potential causes of death being investigated include other diseases or pathogens caused by viruses or bacteria; biotoxins caused by harmful algae blooms; pollution or chemicals, especially from concentrated spills; ship strikes; or acoustic trauma from ships or other infrastructure, he said.

"All indications show there's something serious going on."

Determining a Cause of Death

The spike follows a general trend in more dolphin strandings—or, in scientific speak, unusual mortality events—that have occurred in recent decades in the United States.

In the northern Gulf of Mexico, for instance, where there's an ongoing unusual mortality event, 1,031 dolphins and whales have washed up dead since February 2010. (Also see "Dolphin-Baby Die-Off in Gulf Puzzles Scientists.")

The "concern is we're doing more and more to protect dolphins from harm, yet dolphin strandings are on the rise," said Matthew Huelsenbeck, a marine scientist at the nonprofit Oceana.

"No one seems to have a solid grasp as to what's going on."

But many are working to find out. For example, NOAA has a stranding network of experts who report and collect the corpses of recently deceased dolphins in an effort to determine causes of death.

A corpse is first taken into the lab for evaluation and basic triage to see if it has any visible marks that may point to the cause of its demise. Next, a tissue sample is taken and tested for viruses, which could identify a direct cause.

Then there's a longer-term investigation that involves testing blubber and organs, such as kidneys, for traces of heavy metals. Studies have shown that stranded dolphins have heavy metals in their systems.

"Dolphins are some of the most toxic animals on the planet, and it makes their immune system compromised because they're carrying so many heavy metals and toxins that accumulate in the food web," noted Huelsenbeck. (See "The Secret Language of Dolphins.")

Pneumonia often occurs in dolphins with low immunity.

"Just like in humans, if you have certain afflictions affecting your immune system, you're more susceptible to pneumonia," he said.

What's more, he noted, most of the East Coast dolphin deaths have occurred in areas with heavy human footprints, like the Chesapeake Bay.

"Possibilities Wide Open"

Gregory Bossart, the Georgia Aquarium's chief veterinarian and pathologist, has been studying the impact of infectious disease and pollutants on bottlenose dolphins in Florida's Indian River Lagoon (map) for several years.

He's found that many of the lagoon's dolphins carry toxic mercury at 20 times the level permitted in human food by the U.S. government.

The dolphins there have been suffering from a host of diseases, including new papilloma and herpes viruses and fungal diseases. Some of the diseased animals share a "profoundly" suppressed immune system, he said, likely caused by the dolphins' constant exposure to environmental stressors like mercury. (Related: "New Diseases, Toxins Harming Marine Life.")

Even so, Bossart cautioned that no one should jump to the morbillivirus conclusion for the current East Coast deaths before all the information is in—much more pathology work needs to be done in the lab.

"The possibilities are wide open," he said.

Ocean Canaries

Overall, the experts pointed out that the dead dolphins may be alerting us to troubles in our oceans.

Said NOAA's Spradlin, "Marine mammals are like the canary in the coal mine"—many bottlenose dolphins live on the same coasts and eat the same fish that we do.

"Our first mandate is to protect the dolphins, but the underlying bigger picture is if things are hurting these animals," he said, "[they] could also be hurting people as well."

6 comments
Maureen Frere
Maureen Frere

Years ago there was a documentary on TV about how our Governments US and Canada got rid of thousands of barrels of PCB's after WW-2, by dumping them in the ocean. Could this be part of the cause? And, why would they (our Governments) not be accountable for such action? 

James Pulliam
James Pulliam

I'm guessing algae blooms from the enormous amount of freshwater flowing into the ocean this year from the record rainfalls in the southeast.  I know here in Florida we are having a crisis with freshwater runoff from Lake Okeechobee killing off dolphins, fish, manatees, and getting hundreds of people sick in the Indian River and especially St. Lucie River.  Instead of the water flowing south into the everglades like it is supposed to, they are pumping it east into the St. Lucie estuary.  Why?  Because Sugar Farms are south of Lake O.  Rather then flood the already subsidized, non-profitable sugar farmsx we pollute one of the most unique ecosystems in the world.  I guess the taxpayer supported sugar farmers have a little more cash to spend on lobbyist then environmental groups do.

Marshall Ambros
Marshall Ambros

Deepwater Horizon oil spill anyone? Ever heard of Corexit? These are migratory dolphins you say? Two bets they spend time feeding in the Gulf.

"Corexit used during the BP oil spill had increased the toxicity of the oil by 52 times." Just read the Corexit "Studies" section on wikipedia.

Paige Munson
Paige Munson

With rising pollution levels in the ocean it isn't surprise that dolphin deaths have been occurring at an alarming rate. We need to take ocean cleanup plans very seriously, and increase their intensity.

Marc T.
Marc T.

@Paige Munson What are we to do about the radiation leaks into the Pacific Ocean by the damaged Fukushima Nuclear Plant in Japan?     Considering that there are ocean currents that traverse the planet, the radiation could have already spread globally in the seas and oceans.  Might not marine life such as the dolphins be actually suffering from the radiation?  Our food supply from the oceans and seas could already be contaminated, for all we know.  

There is little transparency over the Fukushima radiation leakage shown by the Japanese Government.  Other governments, the USA included, are not any more helpful or forthright in this regard, understandably to avoid sowing mass panic.  What're we, the small minnows of humanity, to do?

Delaney Jones
Delaney Jones

@Marc T. 

It's Not radiation from Fukushima. Think about this, you have a two liter bottle of water in front of you. You put to drops of dye in it. Now does the whole bottle of water change color? No because there is more water than dye and like the dye the radiation is deluded so much that it is not harmful like you. Let the Japanese Government do their thing and maybe you should focus on your on government.

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