THOUSANDS of dolphins have washed up dead on Peru’s beaches this year in what could be the world’s largest reported mass dolphin die-off.
The body count could be as high as 2,800 based on volunteer’s observations.
The biggest beaching was on March 10 when staff from a marine coastal reserve, in Piura, just south of the Peruvian border with Ecuador discovered about 1,500 dead dolphins.
On March 27, 615 dolphins washed up dead on beaches near the city of Lambayeque, Peru.
Peruvian experts believe the culprit for the mass killing could be acoustic surveying by companies looking for undersea oil. The blasts can damage the dolphins’ ears and other organs, making them confused and disorientated.
A British environmentalist believes the deaths may have been caused by fishing nets, reflecting similar incidents that happened on the British and French coasts in the late Eighties and early Nineties.
Others suggest that a deadly virus could be responsible. Another theory is that pollutants have weakened the animals’ immune system making them vulnerable to the slightest infection. Or they may have died after feeding on fish that had eaten toxic algae.
About 90 per cent of the dead dolphins are long-beaked common dolphins, which had probably migrated from Central America to feed on fish in Peru’s nutrient-rich waters.
The rest are Burmiester’s porpoises, a deepwater species that comes inshore to calve. The dead porpoises that have been found were pregnant, had recently given birth or were calves.
Many of the animals are thought to have washed ashore dead and some of the carcasses had been butchered for their meat by people living nearby.
Peruvian vet Dr Carlos Yaipen-Llanos, who has examined some of the dolphins, thinks the animals may have been killed by the impact of off-shore oil exploration and drilling in the region.
He is taking samples from the dead dolphins for analysis and says acoustic testing could have led to their demise.
Exploration companies use canons mounted on the back of ships to blast air at the seabed. The resulting echo is recorded to determine if there is any oil beneath. But the low frequency sound generated is harmful to dolphins.
“The animal would become disorientated, would have intense pain and would have to make a great effort to breathe,” said Dr Yaipen-Llanos.
“The research needs to be completed to give an ultimate conclusion. Evidence so far points to acoustic impact, however, we are also reviewing if any diseases added to this unusual mortality event,” he added.
Mark Simmonds international director of science at the Whale and Dolphin Conservation Society (WDCS) said: “These events remind me of the time we saw mass strandings of a sister species in Europe in the late Eighties and early Nineties. These pointed to a major fisheries incident offshore where short-beaked common dolphins were killed by nets and washed up dead and decomposing.”
When trapped underwater dolphins close their blowholes and usually suffocate rather than drown.
Simmonds said the global estimate for fishing-related deaths in whales, dolphins and porpoises is 300,000 annually. The majority are never seen but decay at sea.
The Eighties saw a big increase in big pair trawl fishing, where huge nets are dragged between two boats to scoop up vast quantities of fish.
Simmonds said: “Pair trawling went big scale using nets the size of aircraft hangers. Thousands of dolphins attracted to the same fish as the fisherman were targeting were injured by the nets and washed ashore dead.”
Gill nets, which are static nets that stretch for many miles, may have also added to the casualties.
“Climate change may also be a contributing factor. Dolphins migrate to different areas to mate, have babies and calve and a change in water temperature may have diverted their paths where they clashed with the nets,” Simmonds added.

Extra details:
– It is illegal to hunt dolphins for food in Peru although it goes on with impunity. The meat is sold on the black market as sea pig.
– Thirty-four of the world’s whale and dolphin species are found off the coast of Peru, 17 if which are dolphins. The most common of these is the bottlenose dolphin.
– In 1987 and 1988 about 700 bottlenose dolphins died along the along the Atlantic Coast from New Jersey to Florida. Scientists concluded that the dolphins died after infection due to weakened immune systems.
– In the early Nineties several thousand striped dolphins died in the Mediterranean. A morbillivirus was blamed, but immune suppression was also suspected since the dead had higher concentrations of contaminants than the ones that survived.
– Hunting dolphins for food is illegal in Peru, though it is done with immunity and is thought to be increasing. Eating the meat, which is sold as sea pig, is thought to cause diabetes, and much of it is heavily contaminated with pollutants.
– Dolphins live in a world of sound using sonar to navigate, communicate and hunt food. If this is disturbed, they are liable to strand.
– The biggest stranding in the UK happened in July last year, when 44 pilot whales beached in Balnakiel Bay, Durness, Scotland.
– A mass stranding in Cornwell in 2008 was linked to military sonar exercises.