Scientists looking into the longest-running dolphin die-off on record in the Gulf of Mexico say that oil from the BP drilling disaster likely played a “significant” role in killing many of them.
In a study published Wednesday, a team of researchers from the National Oceanic and Atmospheric Administration found that dead dolphins that washed ashore in areas hardest hit by the oil spill between 2010 and 2012 suffered from damage to the adrenal gland or bacterial pneumonia. The damage was likely caused by dolphins inhaling or ingesting oil as they surfaced to breathe, researchers said.
“These dolphins had some of the most severe lung lesions I’ve ever seen in wild dolphins,” said Dr. Kathleen Colegrove, the study’s lead veterinary pathologist.
The study is part of an ongoing investigation into the massive die-off in the Gulf, stretching from the Florida panhandle to the border of Louisiana and Texas. It started just before the Deepwater Horizon drilling rig exploded 40 miles offshore. Researchers said Wednesday they believe earlier deaths were tied to water temperatures and salinity. Ongoing deaths have increasingly pointed to oil — at least three million barrels gushed into the Gulf over 87 days — as the most significant cause of death and illness in dolphins.
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“Basically it makes a direct link to the oil,” said NOAA spokesman Ben Sherman.
BP executives disputed the findings, noting that numerous studies over several decades show dolphins frequently die from respiratory ailments. Researchers also used a small sample set: just 46 dead dolphins. And despite a Freedom of Information Act request, NOAA has so far refused to release reports on “hundreds” of other dead dolphins, BP senior vice president Geoff Morrell said in a statement.
“The data we have seen thus far, including the new study from NOAA, do not show that oil from the Deepwater Horizon accident caused an increase in dolphin mortality,” he said.
But for researchers, the latest findings provide an important link in “the chain of evidence,” said lead author Stephanie Venn-Watson, a veterinary epidemiologist at the National Marine Mammal Foundation.
For the study, researchers examined dolphins that washed ashore near Barataria Bay, Louisiana, a marshy bay just west of the Mississippi River Delta hit hard by the spill. Half suffered from adrenal damage, which can make dolphins ill-prepared for stresses like pregnancy or cold temperatures. When researchers widened their inquiry to include the spill’s entire footprint and dolphins washing ashore on the Louisiana, Mississippi and Alabama coasts, they found one in three dolphins suffered from the lesions compared to just 7 percent in populations outside the spill.
Researchers also found that one in five dolphins in the oily water had bacterial pneumonia that caused or contributed to their deaths. Because the number of deaths has been so high, researchers concluded that neither condition could have existed before the spill.
“It wouldn’t be sustainable for a population,” Venn-Watson said.
Researchers say they are continuing to investigate the deaths to determine what long-term damage the oil may cause to the dolphin population.
“This is not something normal for dolphins,” Venn-Watson said.