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Massive Die-off of Dolphins in Peru

The Peruvian government has released a report on the mass mortality of at least 900 dolphins along the coast of Peru that states that “natural causes” and “evolutionary forces” were the cause of death.

BlueVoice, which has funded extended and extensive research conducted by Peruvian veterinarian and marine mammal expert Dr. Carlos Yaipen Llanos, believes that conclusion is nonsense. We present here a narrative history of the mortality event and Dr. Yaipen Llanos’ hypothesis that acoustical trauma followed by rapid ascent leading to catastrophic decompression is the most likely cause of death. Dr. Yaipen Llanos makes no assertion that seismic testing for oil is associated with the dolphin mortality. However BlueVoice suggests that this form of extremely loud testing makes the seismic tests a primary “element of interest”. Seismic testing was taking place in approximately the same time frame and geographical location as the dolphin mass mortality.

We stress that Dr. Yaipen Llanos has made no assertion that the mass mortality event was caused by seismic testing by oil companies.

It should be noted that some highly regarded experts who question Dr. Yaipen Llanos’ conclusion of acoustical trauma/decompression syndrome, freely admit that they have very little information to assess. Neither do they have an alternative hypothesis.

Hardy & Carlos w/ dead baby dolphin
The Story As Seen By Hardy Jones Of Bluevoice.Org And Dr. Yaipen Llanos Orca Peru.

During February 2012 rumors began circulating that hundreds of dolphins were dying along the northern coast of Peru. But the beaches are remote and no one had actually confirmed the rumors and certainly not made a reconnaissance. BlueVoice Executive Director Hardy Jones flew to Peru where he joined Dr. Carlos Yaipen Llanos of the marine rescue organization ORCA. In order to verify the number of dolphins stranding on the northern beaches of Peru they traveled north from Chiclayo/San Jose. They counted 615 dead dolphins in 135 kilometers. They thus verified that the die-off that had been rumored was a tragic reality.

BlueVoice has funded an ongoing investigation into the cause of the mortality, supporting Dr. Yaipen Llanos in his efforts to necropsy as many dolphins as possible. Here are the results of his investigation.

Hardy views necropsy


Initial conclusions from research on dolphins stranded in northern Peru:

Dolphins died due to acoustical trauma and decompression syndrome.


• Between March 26th and April 26th, 2012, in a coordinated effort with the Peruvian Ecological Police, ORCA and made several expeditions to the "Stranding Zone", covering up to 135 km of deserted beaches and confirming the largest mass stranding of dolphins ever in South America.



To verify that the information on the stranding was correct, Dr. Yaipen-Llanos and Jones joined in a scientific investigation into the cause of death of the dolphins. Successive expeditions during the month of April confirmed continuation of the mass stranding and expanded the number of visually confirmed dolphin deaths to 747.

In addition, on April 27th  2012, ORCA confirmed that dolphins are still being hunted and eaten by fishermen. BlueVoice will report further on this.

In that week, decaying carcasses continued beaching on the "stranding zone."

The affected species found in all the expeditions were:

• Long-beaked common dolphin (Delphinus capensis) - 91% of stranded animals.
• Burmeister’s porpoise (Phocoena spinipinnis) - 9% of stranded animals.


Dolphin bladder - huge bubble compressing vein & artery

Dolphin liver - bubbles are replacing normal tissue

Mandibular blubbler of baby porpoise - bubbles spreading in the normal tissue, plus blood vessels are congested and hemorraghic

• The necropsy procedures and report that ORCA uses for sampling, macroscopic and microscopic analysis is established for marine mammals by the U.S. National Marine Fisheries Service (NMFS) and the U.S. Fish and Wildlife United States (FWS).

• To perform research and analysis of samples, ORCA implemented a Diagnostic Laboratory
• ORCA performed 30 necropsies taking into account the degree of decomposition and the viability of samples for diagnostic purposes. The necropsies were performed on the beach since the full body of the dolphins could not be transported. Fresh and viable samples were collected as quickly as possible – always a priority in marine forensics.
• The necropsy included examination of general body condition, injuries, or external malformations, natural cavities, abdomen, chest, neck and head.
• To prevent misdiagnosis, we used soft tissues of those bodies in fresh condition in order to have a clear view of the cellular structures and identify lesions in the tissues.
• We found that stranded dolphins had the following signs:

a. Bleeding in the middle ear.
b. Simple fracture and cracks in the middle ear (periotic) bones.
c. Hemorrhage and bubbles in mandibular fat (where dolphins perceive incoming sounds)
d. Massive invasion of air bubbles which displaced the normal tissue of vital organs such as lungs, liver, kidney, bladder and blood vessels.
e. Pulmonary emphysema: air bubbles, bleeding and massive destruction of lung tissue.

According to these medical findings, the dolphins suffered from acute decompression syndrome that produced injures associated with acoustic impact.

In the case of this unusual mortality event, only two cetacean species were affected because only these two species were in the range of the potential sound wave, which was released in several distinct moments that translated into a long period of time over which the dolphin die-off occurred.  The presence of both long beaked common dolphins and Burmeister’s porpoises in the ocean surface is associated with the seasonality of each species. While 37 species of cetaceans live in Peru, these are not found in one place at the same time, but spread throughout the year in different areas of the ocean.

The dolphins and porpoises died in a focalized area. They all died off shore. They did not die at the same time. However, all the dolphins that went through forensic analysis produced the same medical findings which indicates that the cause of death was not produced once, but multiple times and in very distinct moments while the dolphins were in the area. This was possible to assess through the condition of the carcasses that correlate the strandings to a long period of time. No strandings of dolphins outside the “stranding zone” were found with similar findings. 


• VIRUS: None of the stranded dolphins showed external signs of viral disease. Internally, none of the necropsied dolphins had findings consistent with viral disease in their bodies. In the case of viral diseases, when they cause the death of the animal, they must necessarily produce a "viremic phase" or signs of infection with macroscopic and microscopic typical clinical picture of the disease, which was not found in dolphins reviewed. We did not find fluid in the lungs (edema), or intestinal necrosis or hyperplasia in the bladder, plus there was a notable absence of the typical viral inclusion bodies.

If the case of a viral infection, especially if it was Morbillivirus, strandings would have occurred in larger quantities and would affected a larger number of marine mammals species, sparking a pandemic alert as it happened in other unusual mortality events associated with this virus.

• ILLNESS: We found no signs consistent with bacterial diseases or poisoning affecting the digestive system.

• Starvation: It is not possible that the beach stranded dolphins died from starvation because the bodies show good fitness (subcutaneous fat present) and no stomach damage or gastritis was found as is associated with prolonged fasting.


• So far there is no virus that could pass or transfer zoonotically from marine mammals to birds in the area.
• Where acoustic impact is the cause of death of dolphins, this impact does not occur in birds because they handle different sound frequencies and they spend little time with their heads underwater.


• 40% of known cetacean species in the world transit through Peru.
• Over 90% of deaths of dolphins in Peru are caused by human aggression/interaction.
• The stranding of dolphins in Peru during the first quarter of 2012 is a warning. On this occasion the impact was on dolphins and porpoises. It would have been other species or whales at another time of year.
• The Congress of Peru has the opportunity to enact the Law 4248 for Animal Protection and Welfare to strengthen mechanisms to protect dolphins and animals from human impact. Currently, this law has been filed in the Congress and is awaiting disposition.

We can do a Spanish version of Carlos press release

Necropsy microphotos


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