Expert Links Dolphin Deaths to Sonar Testing

Did offshore oil exploration play a role in the recent deaths of nearly 900 dolphins off the northern Peruvian coast? Peru’s fisheries minister said last week that government scientists had ruled that out as a possibility and that the dolphins probably died of natural causes. But a marine veterinarian and conservationist who examined many of the corpses contends they were probably harmed by sound waves from seismic tests used to locate oil deposits. dolphin

As we reported earlier this month, the dolphin deaths, which overlapped with a large die-off of seabirds, have been the focus of intense speculation in Peru and around the world.

The marine veterinarian, Carlos Yaipen-Llanos, who is president of the conservation group Orca Peru, said in an interview that necropsies that he and his colleagues performed on three separate expeditions indicated that the dolphins examined were bleeding in their middle ears and had suffered fractures there. They also had gas in their solid internal organs and severe acute pulmonary emphysema, symptoms consistent with death from decompression sickness — that is, the bends, he said.

“The animals died from decompression sickness caused by acoustic trauma,” he said.

That directly contradicts the results of the official investigation, carried out by the Peruvian Ocean Institute, known as Imarpe. The government says the institute had ruled out starvation, poisoning and seismic testing, and that an unknown disease might be the culprit.

As we have noted here on the Green blog, experts on strandings say it is not always possible to determine what causes a die-off of dolphins or whales.

Dr. Yaipen-Llanos said he and his colleagues performed necropsies on 30 dolphins found on a 85-mile stretch of beach, examining all of their organs. Seven of them had just died, he said. By contrast, the government scientists performed necropsies on just two dolphins, analyzing three organs of each, Dr. Yaipen-Llanos said.

He said that newly dead animals were found on each of the group’s three expeditions. Considering the findings,“we believe that a strong source of sound was continuously in the area,” he said. “It wasn’t just once.”

The government insists there was no seismic testing in the areas where the dolphins died. But a fisherman interviewed this month said seismic testing had been carried out in the area around the time the dolphins began dying. And El Commercio, Peru’s biggest newspaper, has reported that the Peruvian Navy gave permission for foreign companies to carry out seismic testing in November, not long before the first dead dolphins began washing up on shore.

Dr. Yaipen-Llanos said the middle ears of all 30 animals – both long-beaked common dolphins and black porpoises — had visible fractures ranging from slight to serious. The animals had bubbles in their lungs, livers, stomachs, bladders, skin, spleens and blubber, he added. “Over all, there was mass destruction of tissue by bubbles,” he said.

“I was expecting a viral infection,” Dr. Yaipen-Llanos said. “We all were, including our colleagues overseas. But we found no clinical signs of that.”

Blood tests for one suspected agent, morbillivirus, were negative, he said, and there were no indications of bacterial infection.

Decompression sickness has been well-studied in humans. If a scuba diver ascends too rapidly, the nitrogen that he has absorbed from his air tank will cause excess bubbles to form in his veins and tissues. The effects can be deadly.

Scientists once thought marine mammals like whales and dolphins were relatively immune to decompression sickness. But a recent study in the Proceedings of the Royal Academy said researchers had recorded deaths among marine mammals as a result of decompression sickness, primarily among beaked whales “in association with anthropogenic activities such as military sonar or seismic surveys.”

The science remains poorly understood. But the researchers suggested that bubbles might form as result of “a direct physical effect of intense sound (such as rectified diffusion) that might destabilize gas nuclei” in tissues that were supersaturated with nitrogen. Another possibility is a behavioral change in the mammals’ diving profiles that causes the saturation of tissues and subsequent “severe gas-bubble formation,” they wrote.

In any case, one of the researchers, Michael Moore, a veterinarian and whale biologist at the Woods Hole Oceanographic Institution in Falmouth, Mass., said in an e-mail that bubbles can be present normally or be part of “a pathological process.”

Bubbles can form after putrefaction of a corpse, for example, he said.

Dr. Moore cautioned that he did not want to comment on the specifics of the Peruvian cases because he had not seen the data on which Dr. Yaipen-Llanos and the government had based their conclusions.

Dr. Yaipen-Llanos said in the interview that the fresh dolphin carcasses had excess bubbles as well that differed from putrefaction bubbles.

He suggested that rather than startling the animals and leading them to ascend too rapidly, sound waves may have knocked the supersaturated nitrogen out of the dolphins’ blood, forming bubbles inside their bodies.

On another front, he said he shared the government’s view that recent die-offs of seabirds were unrelated to the dolphin deaths. The birds are thought to have starved because their primary food source, the anchoveta, has been in short supply. The shortage of anchoveta is attributed to an El Niño-like effect that has left coastal water temperatures above average.

Dr. Yaipen-Llanos said that if the El Niño-like weather pattern returns, the anchoveta shortage in Peruvian waters could worsen, with an extreme effect on the black porpoise.

The long-beaked common dolphins, which range from Peru to Costa Rica to the Galápagos Islands and to Hawaii, would simply move on if their prey were in short supply, he suggested. But the black porpoises, endemic to South America, would probably face starvation, he said.

Written by The New York Times

Leave a Reply

You must be logged in to post a comment.