LIMA, Peru — Dolphins have been dying along this South American country’s northern coast in unprecedented numbers. Conservationists say the die-off could be the result of seismic testing by a private oil company.

The bodies of about 3,000 animals, principally short-beaked common dolphins, have washed up on beaches since early February, according to research conducted by veterinarian Carlos Yaipen-Llanos, founder and scientific director of Peruvian marine conservation group Orca. The animals have no outward signs of trauma and researchers are continuing to investigate possible causes.

Nevertheless, some experts are pointing the finger at seismic testing used by Houston-headquartered oil company BPZ in that stretch of the Pacific. The technology involves analyzing the echoes of underwater explosions for evidence of oil reserves.

Yaipen-Llanos said bubbles and blood had been found in the sinuses of some of the dolphins.

That’s an indication of the bends, or decompression sickness, potentially caused by the animals’ panicked rapid ascent to the surface to escape the noise of the explosions.

“This is the worst incident of mass dolphin mortality I am aware of in the Americas,” Yaipen-Llanos told GlobalPost.

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He added that the sound of the seismic testing can travel more than 100 miles in the open seas and the frequency fell right in dolphins’ normal hearing range.

Patricia Majluf, the deputy minister of fisheries, told the Peruvian congress last week that BPZ executives in a meeting had been unable to give her clear answers regarding the effects of their oil exploration on marine mammals.

“BPZ’s environmental impact study should have included a detailed description of the area of influence and the level of decibels that there would be in the impact zone,” she added.

BPZ failed to respond to GlobalPost’s requests for comment. However, in a statement, the company argued that the dolphin deaths had begun before it initiated seismic testing.

“Regrettably, similar deaths have also been reported globally, including Brazil and various states on the Atlantic Coast of the United States, more recently Cape Cod, Massachusetts,” the statement read.

But Sue Rocca, an American marine biologist with the Whale and Dolphin Conservation Society, the leading international environmental group dedicated to marine mammals, agreed with Yaipen-Llanos’ suspicions.

"There are all the tell-tale signs of seismic [testing]” she told GlobalPost, adding that US Navy divers had been known to have seizures after being exposed to seismic testing.

“It is an extremely painful experience for dolphins. They are very acoustic animals and these are huge, frightening sounds. For years, we thought marine mammals couldn’t get the bends. Unfortunately, we now know that that is not true.”

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However, Rocca sounded a note of caution, saying that seismic testing would normally result in other marine mammals, such as whales, also being affected. So far, there has been no sign of that.

Other possible causes could include poisoning or a red algae bloom, which can be triggered by pollution.

“One way or another, this is probably caused by humans,” she added. “Marine ecosystems are delicate places but we keep messing with them, and dolphins are very sensitive to these changes. They are also very mobile but there is a limit to where they can go to escape pollution, seismic testing or other disturbances of their habitat. It’s not good when they just displace to shipping lanes, for example.”

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The deaths have also called into question the Peruvian authorities’ ability to protect the marine environment. The Institute of the Sea of Peru (IMARPE by its Spanish initials), the government agency in charge of marine and fisheries research, has claimed that just 324 dolphins have died, despite the tally of 3,000 compiled by independent experts including Yaipen-Llanos, and confirmed by Rocca.

As BZP indicated in its statement, the Peru deaths are just the latest in a grim time for dolphins, including mass beachings and deaths around the world. About 250 have beached in Cape Cod this year, compared to an annual average of 38. Meanwhile, since early 2010 the death toll in the Gulf of Mexico is up nearly tenfold, a trend that began even before the BP oil spill.

“It has been a crap year for dolphins,” said Rocca. “Have we reached a tipping point? We don’t know yet but it is possible.”