The death of about 3000 dolphins on a stretch of Peruvian coast in recent months is being blamed on a controversial oil exploration technique.

However other experts are not convinced, and believe a virus or pathogen may be responsible for one of the largest dolphin die-offs recorded.

So far this year, thousands of dolphins have washed up on a 135km stretch of coastline in Lambayeque, in northwestern Peru.

Numbers differ between reports, with some reporting more than 3000 of the mammals have been found dead in the past three months. Others have the figure around 2800.


Ninety percent of the dead are long-beaked common dolphins, while the remainder are Burmeister's porpoises.

Veterinarian Carlos Yaipen, director of Lima's Scientific Organisation for the Conservation of Aquatic Animals told Peru21 the deaths were the result of sonar testing for oil.

"The oil companies use different frequencies of acoustic waves and the effects produced by these bubbles are not plainly visible, but they 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.

All of 20 of the mammals Yaipen examined had middle ear hemorrhaging, fractures to the ear's periotic bone, lung lesions and bubbles in the blood. Yaipen said this indicated the animals were injured but still alive when they beached.

According to a report in the Environmental Health News, oil exploration has been undertaken in the region, however it is not known whether seismic testing was underway.

Peter Ross, a research scientist at Canada's Institute of Ocean Sciences in Sidney, British Columbia, told the Environmental Health News stress or toxic contaminants may have made the dolphins more vulnerable to pathogens. He said there may be two or three factors responsible for the deaths.