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What’s Killing the Dolphins of Peru?

So far this year, according to the newspaper Peru21, more than 3,000 dolphins have washed up on the beaches of the northern Peruvian region of Lambayaque.

Scientists are generally agreed that the cause of death is sonar from companies probing for oil.

Carlos Yaipen, science director for the Scientific Organization for Conservation of Aquatic Animals (ORCA), the deaths are due to “marine bubbles” – acoustic pockets that form when sonar is used to map what lies below the ocean floor.

“The oil companies use different frequencies of acoustic waves and the effects produced by these bubbles generate effects later in the animals. That can cause death by acoustic impact, not only in dolphins, but also in marine seals and whales,” Yaipen said.

In just the last few days, 481 dolphins were found on the beaches.

Sonar has been under scrutiny for many years as a major hazard to marine mammals. In 2003, a study by British and Spanish scientists reported that they had found gas bubbles in the internal organs of 14 whales that were found on a beach in the Canary Islands.

These kinds of bubbles are typical of decompression sickness (the bends) suffered by human divers who surface too quickly. The whales in the Canary Islands had become stranded four hours after the use of military sonar during an international naval exercise. Post-mortem examination revealed bubbles in blood vessels in their brains and livers, as well as clots of fat in blood in their brains, livers, lungs, kidneys and other tissues. Some of the blood vessels had exploded.

While no specific oil company has been blamed for the dolphin deaths, Offshore magazine reported last month that the company BPZ Energy had been conducting exploration in the region:

A new 3D seismic survey has been under way for a month on offshore block Z-1, and should be completed during 2Q 2012, followed by a period of processing and interpretation. The aim is to improve understanding of the geology of both fields, and to better define other prospects on the block for future exploration.