Peru’s Drawn-Out Dolphin Mystery

As I report in The Times with Andrea Zarate, officials in Peru are struggling to understand why hundreds of dolphins and seabirds have died over the last few months.

While the answers are not yet known, 2012 has clearly not been a good one for dolphins where such ‘‘unusual mortality events’’ are concerned.

From January through April, at least 214 common dolphins were stranded on Cape Cod, and at least 141 of them died, according to the International Fund for Animal Welfare. The National Oceanographic and Atmospheric Administration says meanwhile that the  magnitude of strandings in the northern Gulf of Mexico since the BP oil disaster has been ‘‘unprecedented.’’

Some Peruvian fishermen say that 3,000 or more dolphins have died off the country’s northern coast since late last year; the government puts the number at fewer than 900.

The odds are good that many more such events go unreported around the world. What causes marine mammals to die en masse? NOAA notes a number of possible causes, including infectious disease, parasite infestation, starvation (associated with El Niño events), pollution, injuries and algal blooms that release biotoxins.

Manmade noise like seismic testing for oil and natural gas with high-tech sonar equipment, is also thought to contribute to marine mammal deaths.

Peruvian officials have said they believe the culprit this time is an infectious disease, most likely a morbillivirus, which comes from the same family of pathogens that cause measles and canine distemper.

We asked several scientists, including Frances Gulland, a senior scientist and veterinary care expert at the Marine Mammal Center in Sausalito, Calif., who is also a commissioner of the United States Marine Mammal Commission, what she thought of the morbillivirus theory. Dr. Gulland said by e-mail that it was a “possible” cause but that she could not hypothesize further because she had not seen any data.

That was puzzling, because one of the reasons that we sought out the Marine Mammal Center was that Peruvian officials had told us and others that the commission had confirmed the virus theory. That was incorrect, but that misinformation typifies the apparent confusion in Peru. Strangely, the country does not seem to have done much to seek help on the question beyond its own borders, and many Peruvian scientists told us they had been instructed not to speak with the press. [continue]