Peru’s northern coast is currently the site of one of the biggest Unusual Mortality Events for dolphins ever recorded. As many as 3,000 dead dolphins have been found since January 2012, and more than 1,000 dead seabirds, mainly pelicans, have washed up on shore in recent weeks. And nobody seems to know why.
As nearly every major news source has reported, a cloud of uncertainty surrounds the die-off. Officials from Peru’s federal Ocean Institute are suggesting that the culprit, in the case of the dolphins, is morbillivirus, from a family of viruses linked to previous mass deaths of marine mammals. Others are less certain, and autopsies performed on the dead dolphins have found hemorrhagic lesions in the acoustic chamber and fractures in the periotic bones, pointing towards acoustic impact and decompression syndrome as the cause of death. This would suggest that seismic survey blasts used in oil exploration in the region may be a cause of death. Yet much uncertainty remains, as the New York Times reports:
The discovery of dead animals on beaches near Lima, the capital, in recent days has complicated matters. Over the weekend, the Health Ministry issued an alert advising people to avoid the waters around Lima and to the north, “until we know the cause of the recent deaths of marine species.”
It advised people not to eat raw seafood, an ingredient of the national favorite ceviche, and recommended that people disposing of dead marine animals wear gloves and masks. The warning sowed confusion, given earlier government statements indicating that the seabirds were probably starving rather than falling ill from some disease.
What about the pelicans? Officials maintain that there is no link between the bird deaths and dolphin deaths, and suggest that the birds are dying from starvation due to the scarcity of anchovies caused by rapid warming of waters in the region.
Another hypothesis involves suggests that biotoxins from raw sewage and other pollution may have made its way into the food chain, and both dolphins and pelicans, which consume anchovies, could have been poisoned this way.
“It’s unbearable to walk around those areas,” Mr. Alva said of the rapidly growing towns along the coast. “They dump both their industrial and residential wastes into the ocean without control, without consideration.”
Sophie Bertrand, a marine ecologist at the Research Institute for Development in France who is leading a research project on seabirds and sea lions in Peru, said that if there was a common factor linking the die-offs, it would probably be found in the anchoveta, eaten by all of the species concerned.
Meanwhile the die-offs continue, though in lesser numbers than before.