An independent panel of scientists found that sonar surveying by ExxonMobil in late May 2008 led to the sudden displacement of around 100 whales, of which at least three-quarters died, they said yesterday.
"This is the first known such marine mammal mass stranding event closely associated with relatively high frequency mapping sonar systems," said the report released by the International Whaling Commission.
"Earlier such events may have been undetected because detailed enquiries were not conducted."
The researchers described a "highly unusual event" in which melon-headed whales became stranded in shallow waters in the Loza Lagoon system in northwest Madagascar in May and June
The culprit was named as a high-power 12 kilohertz multibeam echosounder system, or MBES, operated by an ExxonMobil vessel on May 29 about 65 kilometres (40 miles) offshore from the first known stranding.
The five-member independent scientific review panel said the vessel's MBES was "the most plausible and likely behavioural trigger for the animals initially entering the lagoon system."
The sounds would have been "clearly audible over many hundreds of square kilometres of melon headed whale deep water habitat areas."
The report said that seismic airguns, long opposed by environmental groups for the potential harm they can cause to marine life, were not to blame for the event.
"They used the multi-beam echo sounder first. That scared the animals into the lagoon and then the air guns were used afterward," explained marine scientist Matt Huelsenbeck of the advocacy group Oceana.
"So that is not to say that air guns would not have caused it had they been used first. They are even louder than the multi-beam echo sounder."
A spokesman for ExxonMobil said the company disagrees with the findings.
"ExxonMobil believes the panel's finding about the multi-beam echo sounder is unjustified due to the lack of certainty of information and observations recorded during the response efforts in 2008," spokesman Patrick McGinn said in an email.
He added that observers employed by the Madagascar government and the oil giant "were on board the vessel and did not observe any whales in the area."


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