LIMA, Peru -- When a retired fisherman called to report that about 1,500 dolphins had washed up dead on Peru’s northern coast, veterinarian Carlos Yaipén’s first reaction was, “That’s impossible.”

But when Yaipén traveled up the coast last week, he counted 615 dead dolphins along a 135-kilometer stretch of coastline.

Now, the death toll could be as high as 2,800, based on volunteers’ counts. Peru's massive dolphin die-off is among the largest ever reported worldwide.

The strandings, which began in January, are a marine mystery that may never be unraveled. Experts say the causes could be acoustic impact from testing for oil or perhaps an unknown virus or other pathogen. Little marine research takes place in Peru, and even in the United States, of 55 marine mammal strandings since 1991, the National Oceanographic and Atmospheric Administration (NOAA) has classified 29 as “undetermined.”

All of the 20 or so animals Yaipén has examined showed middle-ear hemorrhage and fracture of the ear's periotic bone, lung lesions and bubbles in the blood. To him, that suggests that a major acoustic impact caused injury, but not immediate death. Most of the dolphins apparently were alive when they beached, or had died very recently.

“The animal would become disoriented, would have intense pain, and would have to make a great effort to breathe,” he said of the injuries.

Other experts say there is not enough evidence to draw a conclusion.

Stress or toxic contaminants can make marine mammals more vulnerable to pathogens such as viruses, according to Peter Ross, a research scientist at Canada’s Institute of Ocean Sciences in Sidney, British Columbia.

In a mass die-off, “there might be a smoking gun, but often we find that it’s two or three or four factors,” said Ross, who is one of the world’s leading experts on the effects of toxic contaminants in marine mammals.

Persistent organic pollutants, such as polychlorinated biphenyls or PCBs, the pesticide DDT, dioxins and flame-retardants accumulate in fish, and the concentrations are magnified as they move up the food web to top predators such as dolphins, seals and sea lions.

Laboratory studies of rodents and cells harvested from marine mammals show that PCBs and dioxins “are very immunotoxic,” Ross said. “The immune system is exquisitely sensitive to exposure to environmental contaminants.”

Animals with weaker immune systems could be more vulnerable to stress from noise or climate change, or to diseases such as leptospirosis, brucellosis or distemper, Ross said.

Scientists say that immune suppression from PCBs and DDT contributed to several marine mammal die-offs in the late 1980s and early 1990s, including dolphins along the Atlantic Coast and in the Mediterranean Sea, and harbor seals in northern Europe.

Yaipén, founder of the Lima-based Scientific Organization for the Conservation of Aquatic Animals (ORCA), knows of no studies of pollutants in Peru’s marine mammals. He has stored tissue samples from some of the beached dolphins but ORCA – a largely volunteer organization – has not yet been able to arrange for analysis.

Peru’s entire coast is a desert, its sandy beaches punctuated by peninsular cliffs and dotted with tiny fishing villages. On one trip up the coast, Yaipén said he initially counted a few dolphins every 150 meters, then every 10 or 20 meters.

The first account of 24 dead dolphins came on Jan. 21 in Piura -- on the north coast, just south of the border with Ecuador -- the same region where the 1,500 were reported by the staff of a marine coastal reserve on March 10. Another 416 were counted in Piura on March 21. More than 870 were spotted in February and March on beaches in the Lambayeque region, south of Piura.

Since it's ongoing, it may wind up being the largest dolphin die-off ever reported.

In 1987 and 1988, about 700 bottlenose dolphins died along the Atlantic coast from New Jersey to Florida. That may have depleted the coastal stock by more than 50 percent. Scientists concluded that the dolphins, which had bacterial and viral infections, were immune-suppressed.

Then, in the early 1990s, large numbers of striped dolphins – estimated at several thousand -- died in the Mediterranean Sea, starting in Spain. Infection by a morbillivirus was apparently the cause, but immune suppression was suspected, too, since the dead dolphins had higher concentrations of contaminants than ones that survived.

In Peru, two species have been stranded. About 90 percent are long-beaked common dolphins (Delphinus capensis), which swim close to the surface and have probably migrated south from Central America to feast on the abundance of fish in the nutrient-rich Humboldt Current that sweeps Peru’s coast.

The rest are Burmeister’s porpoises (Phocoena spinipinnis), a deepwater species that moves closer to the surface to calve. All the Burmeister’s porpoises Yaipén has recorded have been pregnant or lactating females or calves.

Yaipén worries that pathogens or contaminants in the dolphins could pose a health risk for residents of fishing villages along the coast, who have been cutting meat off the carcasses for food.

If they avoid the blubber, they will avoid most of the toxic chemicals, Ross said, but if the strandings are due to disease, they could be at risk of infection.

After sick and dead bottlenose dolphins washed up on the Louisiana coast recently, the U.S. Bureau of Ocean Energy Management (BOEM) ordered an oil and gas exploration company to suspend seismic testing – which uses air guns to map hydrocarbon deposits on the ocean floor – until May, when calving season ends.

Several oil leases under exploration are located off the coast or Peru where the dolphin strandings occurred, but it was not clear if seismic testing was under way. The offices of Savia Peru, which holds the leases, were closed Thursday, a national holiday in Peru.

A spokesman for Houston-based BPZ Energy said the company has been doing seismic testing since early February in an offshore lot several hundred kilometers north of where the dolphins were found.

Air guns can have “myriad impacts ... on marine mammals,” said Michael Jasny, senior policy analyst at the Natural Resources Defense Council, an environmental group that has urged BOEM to restrict seismic testing. 

Although there has been more analysis of the impact of sonar than seismic testing, studies have linked loud ocean noises to ear and organ damage in marine mammals. Sounds can also change behaviors such as dive patterns – which can result in decompression sickness or “the bends” – or drive them closer to shore, where they could beach if they were disoriented.

“Lots of sound in the wrong place at the wrong time can lead to mass stranding,” Jasny said.

Environmental groups have gone to court several times to challenge the U.S. Navy’s use of sonar in military exercises, arguing that it can change marine mammal behavior and lead to strandings. There has been no information available on whether sonar has been used off Peru’s coast.

If noise is to blame in Peru, sonar could be a more likely culprit than seismic testing, according to Brandon Southall, former director of NOAA’s ocean acoustics program. He said the characteristics of the Peru strandings would be “atypical, but not impossible” for an acoustic-related stranding.

Even if sonar were a factor, the injuries may not be due directly to the impact of the sound. “Animals may react in a way that has a cascade of physiological effects,” Southall said.

This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.

12 Comments

1. 1. Rev.Corvette 08:30 PM 4/6/12

   Thanks for the clear, concise report, damn sad though, I hope the cause of this death wave is soon determined.
   What is the estimated world population of long-beaked common dolphins?
   Land mammals could be next....

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2. 2. Mark5146546 11:54 AM 4/7/12

   “All of the 20 or so animals Yaipén has examined showed middle-ear hemorrhage and fracture of the ear's periotic bone, lung lesions and bubbles in the blood”.
   
   Toxic chemicals don’t facture ear bones.
   
   As was implied at the end of the article, but had struck me in the first paragraph, this was clearly caused by a low-frequency long-range sonar the US navy has been deploying, mostly on submarines, well known to harm cetaceans. There is a small chance it could be another acoustic related phenomenon, but it’s unlikely.
   
   Activist groups, rise! The Cold War is over and Talibans don’t use subs. So the US navy could well ease off on the doomsday gear and give it a rest. We're the hegemon already, we can afford to be a positive influence now.
   
   BAN LOW-FREQUENCY SONAR NOW!
   
   
   
   

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3. 3. daedalus2u 12:29 PM 4/7/12

   Has the composition of the gas been analyzed?
   
   As mammals, dolphins don't have the ability to remove partially soluble gases such as methane except via exchange with air in the lungs which is very slow. Many fish have a gas gland which allows concentration of gas from the blood into the swim bladder, and also fish exchange gases with ambient water.
   
   If dolphins ate something that produce methane in their gut, they would have no way to remove it except through their lungs. When they dive, the methane would dissolve in their blood and migrate from the gut to other tissue compartments, first going through the portal circulation to the liver.
   
   Often beached cetaceans show quite massive bubble formation in the liver. The liver is usually not a site for gas bubbles due to the bends (from nitrogen).

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4. 4. Mark5146546 in reply to daedalus2u 01:03 PM 4/7/12

   Again, methane poisoning does not cause ear damage. That is a smoking gun the cause was acoustic.

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5. 5. Rev.Corvette 08:27 PM 4/7/12

   Is this something that could be caused by "Fracking for OIL??"

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6. 6. Mark5146546 11:38 PM 4/7/12

   
   Here’s what happened. Their ears burst (this is what we know for sure), so this was probably due to a very loud noise, probably low frequency sonar. With their ears burst, their sense of up and down was lost, so they couldn’t breathe properly, which for them requires going up, above the water level. Thus their lungs were eventually bust, and hence the bubbles, which will be made of air if this hypothesis is correct.
   
   It was a very slow and agonizing death, and it is an ongoing thing.
   
   It could perhaps be caused by seismic testing, (not by fracking, which is not seismic and may be harmful mostly by contaminating groundwater) but only if they (all hundreds of them) stayed right next to the test site. I don’t think there are any new fields being developed off Peru right now.
   
   This type of thing is almost invariably caused by this new submarine sonar. It’s a US submarine(s) doing maneuvers off the south pacific coast. Fourth Fleet, if memory serves.
   
   Considering the Cold War is won, the Taliban don’t have a navy, and - lo and behold - there isn’t even any war with Hitler going on right now, perhaps this additional weapon development isn’t absolutely necessary right now. At the very least, maneuvers could try to avoid cetacean areas. If the juvenile testosterone fantasy would be to rule the world and then act as an enlightened despot, perhaps it could be noticed that the ‘ruling the world’ part has been as thoroughly achieved as practicable, by the US, and the ‘enlightened’ part could start already.
   
   
   BAN LOW FREQUENCY AND/OR EXTRA LOUD SONAR NOW
   
   

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7. 7. Mark5146546 11:43 PM 4/7/12

   Sorry: bubbles will be made of air or CO2 (if this hypothesis is correct).

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8. 8. jwhyman 09:51 AM 4/9/12

   One theory that is not cited is that there is a shortage of fish, which would be due to humans. The dolphins may prefer suicide rather than depleting their food source which would led to extinction.

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9. 9. JoyceMitchellme 02:23 PM 4/10/12

   "... showed middle-ear hemorrhage and fracture of the ear's periotic bone, ..."
   
   Does anyone know the kind of force or decibels that would be needed to cause this?
   
   I understand that the periotic bone is very hard and strong with a density similar to teeth. At first, before I googled periotic bone, I was imagining damaged tissue---like a busted eardrum---NOT BONE, which this is.
   
   What decibel of sound would be needed to fracture hard bone?

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10. 10. kallen 08:47 PM 4/11/12

    This can't be good; for us or the planet. What comes to mind is this. Down the chain, oil and the behemoth industries it supports are culpable. The average person, like me, reading and commenting on the news can do something: buy an electric car, invest in alternative energy, eat organic foods and shop with sustainability in mind.......and vote.

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11. 11. sedwin 04:00 PM 4/12/12

    I'm wondering if this could yet be the continuing die off of hundreds of dolphins due to the dispersants used by BP in the Gulf Oil Spill. We know the dispersants have caused heavy metal poisoning in new born and adult dolphins as well as bacterial and other infections in the adult dolphins guts causing deaths and spontaneous abortions and death. Since the dispersants have affected everything in the food chain from fish to plants to coral it hard to tell what long term affects are happening. Before you scream how can bacterial infections or heavy metal infection cause a dolphins ear to hemorrhage and/or fracture please realize dolphins ain't humans. Their ears are much more sensitive and complex. Whereas these things might simply cause severe infections/pain/discomfort to us to a mammal that uses sonar for a living well you can see why the groundings are inconclusive to NOAA.

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12. 12. elriana 03:35 PM 5/25/12

    I'm a geophysicist (researching earthquake hazards, not working for an oil company). In my opinion, naval-grade sonar is a much more likely culprit than airguns. I have been on ships using mid-sized airguns, and I have watched dolphins playing in the bubbles. They follow us for kilometers sometimes and sometimes just check us out and leave again.
    In US waters (or anywhere we acquire seismic images with NSF money) we consider marine mammals in our operations. Often, we have certified spotters (including marine biologists) who look for whales and dolphins and even turtles. I have data gaps where we had to turn off the instruments because we spotted a whale. We also often ramp up the guns slowly, so the noise starts soft and gradually gets louder. That way any animal who is sensitive to the sound can move away slowly rather than fleeing in a panic (and we can test the pressure seals on the airguns). We can't get close enough to shore to force most animals to beach because we can't operate in most waters that shallow.
    I know oil industry is required to use these precautions in some places, but not all. I also know that even the loudest seismic airgun is unlikely to directly harm a large number of animals unless all 1200 of them were in the same 50 ft swath of ocean. Dolphins are smart, and they would move away from such a racket long before it damaged their ears.
    Naval Sonar, however, is in the range of frequencies these animals use for communication and carries over a much longer distance in the water. Sonar can use volumes that are known to be harmful to the animals and many precautions they could take would alert others to their positions (surface spotters on submarines would not work).

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