[OANNES Foro] Dolphin strandings in Peru elude explanation

[Mario Cabrejos]

Dolphin strandings in Peru elude explanation
Barbara Fraser
Ecoamericas - April 2012

Nearly three months after dolphins began beaching themselves on Peru's northern coast in droves, officials still don't know
what caused the massive die-off, and some experts say the deaths may remain a mystery.

Although early reports indicated as many as 2,800 common dolphins (Delphinus capensis) and Burmeister's porpoises (Phocoena
spinipinnis) beached on the coast of the Piura and Lambayeque regions, the official count as of mid-April was 877, according to Vice Minister of Fisheries Patricia Majluf. "We know very little," Majluf says. "Unfortunately, this type of event is occurring more frequently around the world. No one knows if it's a consequence of climate change, pollution" or other factors.

The strandings have coincided with dolphin beachings in the United States along the Louisiana coast and on Cape Cod, Massachusetts, although a spokesperson for the U.S. National Oceanographic and Atmospheric Administration called the events unrelated.

Explaining a stranding takes detective work, but scientists say that in about half the cases, no answer is found. Some experts assert the gradual increase in the number of beachings reported in Peru, which peaked in March, suggests the cause was disease or a biotoxin, perhaps from an algae bloom.

Weighing possible causes

In an April report to Peru's Congress, Majluf said lab tests had ruled out heavy metals and poisoning from agricultural chemicals.
The report says a combination of warmer-thanusual ocean temperatures and significant river runoff, because of heavy rains in the Andes, was creating ideal conditions for algae blooms off Peru's coast, but that no significant blooms had been observed. Tests ruled out three marine biotoxins associated with algae blooms; but the report notes there are several hundred such toxins, so the tests are not conclusive.

Disease is another possible cause of the die-off. Armando Hung, dean of the School of Veterinary Medicine at Cayetano Heredia University in Lima, said April 20 that he had ruled out brucellosis, but was still awaiting results of tests for leptospirosis and morbillivirus. He added, however, that samples were taken from only two cadavers, which were in an advanced state of decay that could complicate analysis.

When reports first surfaced in Peru in February, media and some environmentalists were quick to blame offshore oil operations,
though there were no reports of oil leaks or slicks. Carlos Yaipén-Llanos, a veterinarian and president of the nonprofit Scientific Organization for the Conservation of Aquatic Animals (Orca), examined some of the dead animals and said he suspected acoustic impact from offshore seismic testing, because he found broken ear bones in the dead dolphins he examined.

BPZ Energy of Houston began seismic exploration-which involves firing blasts of air at the ocean floor-in February off the coast of the Tumbes region, north of the beaches where the strandings occurred. A BPZ spokesman said dead dolphins were reported on the beaches before the testing began, and that the company was complying with all Peruvian regulations.

Darlene Ketten, senior scientist at Woods Hole Oceanographic Institution in Massachusetts, says there was a "low probability" that the dolphin deaths were due to seismic exploration. Ketten, who has studied dolphin strandings around the world, said ear bones could be broken when a necropsy is done, and only an X-ray or CAT scan could identify ear damage.

"Strandings of this size are usually related to toxins," Ketten says, adding, however, that about half of dolphin strandings go unsolved. 

"Atypical" for acoustic-impact 

Brandon Southall, former director of the NOAA ocean acoustics program, also said the Peru strandings were "atypical" for a case of acoustic impact. "Investigations [of strandings] are painfully slow because you have to sift through all the possibilities," he says. The dolphin detective work in Peru is even more complicated because there is so little marine research in the country, says Majluf,
a zoologist who spent several years studying sea lion colonies on the country's southern coast. (See "Time to map Peru's marine ecosystems, Majluf says"-EcoAméricas, April '03.) She says it is impossible to compare the number of beachings this year with past years because reliable records have never been kept.

Yaipén-Llanos worries that some residents of fishing villages where dolphins have beached cut up the carcasses and took the meat
home to eat. Because they are high in the food web, dolphins can have high concentrations of heavy metals and chemicals such as DDT, PCBs, dioxins and flame retardants, especially in their blubber. Those metals and chemicals can also accumulate in the bodies of humans who eat the carcasses. They could also weaken the immune systems of marine mammals.

Ultimately, the strandings in Peru may prove to have a combination of causes. Says Peter Ross, a researcher at the Canadian
Institute of Ocean Sciences in Sidney, British Columbia: "Many times, at the top of the food chain, there might be a smoking gun, but often we find that it's two or three or four factors."



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