Deep water sonar blamed for mass dolphin death

Veterinarian Carlos Yaipen of the Research and Conservation of Aquatic Animals (ORCA) looks at a dead dolphin on the shore of a beach in Lambayeque (Reuters)

WED, 04 APR 2012 3:22P.M.

Environmentalists in Peru are warning that an unprecedented number of dead dolphins are washing up on the country's shores because of the use of deep water sonar systems by the shipping industry.

It follows the discovery of 615 of the mammals in the last few weeks along a 135km stretch of coastline.

As many as 3,000 dead dolphins have been found since the beginning of Peru's summer.

Researchers at the Organisation for the Conservation of Aquatic Animals (ORCA), a Peruvian marine animal conservation organisation, said that ships using deep water sonar are to blame for the mass deaths.

After studying the corpses of many of the dolphins, it was noticed that they did not bear marks of external damage caused by fishing practices or signs of poisoning.

Instead, researchers found damage in the dolphins' middle ear bones, which is said to be a sign of decompression syndrome.

"We have been noting that the animals were suffering from acute decompression syndrome - that is to say, a violent death produced by an acoustic boom that disorients the animal and produces haemorrhages which cause the animal to end up dying on the beach," said ORCA director Dr Carlos Yaipen.

The damage is said to come from sonic bursts that are produced by deep water sonar signals sometimes used in the search for petroleum. The bursts can damage animals whose communication frequencies fall in the same range.

US federal regulators are curbing an oil and natural gas exploration company from using seismic equipment that sends out underwater pulses along Louisiana's coast until the bottlenose dolphin calving season ends.

ORCA calculates that the phenomenon represents the highest number of beached dolphins recorded anywhere in the world in the last decade.

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