Most of the dolphins in the northern Gulf of Mexico that have died since the 2010 Deepwater Horizon oil spill suffered severe health problems consistent with petroleum exposure, according to a study backed by the federal government and published in a scientific journal Wednesday.
BP PLC, the main operator of the well that spilled, disputed the paper’s findings, saying the scientists had found no link between the oil spill and the dolphin deaths.
The paper, published in the peer-reviewed online scientific journal PLOS One, focused on 46 bottlenose dolphins found dead from 2010 to 2012 in waters off the coasts of Louisiana, Mississippi and Alabama, which had been hit by the oil spill. The scientists found most of the animals had lesions in their lungs and adrenal glands that caused many to die by disturbing their ability to regulate metabolism and blood pressure, and weakening their ability to fight infection.
The animals all had “significant life-threatening abnormalities” that were “consistent with the effects of petroleum products,” said Kathleen Colegrove, a veterinary pathologist from the University of Illinois who participated in the research.
Ms. Colegrove said some of the dolphins died of bacterial pneumonia. The severity of the disease in the bodies was the worst she had ever seen in 13 years of studying dead dolphins, she said.
Dolphins are highly susceptible to chemical exposure, and infections are more likely because they have large lungs, she said.
Stephanie Venn-Watson, a veterinary epidemiologist with the National Marine Mammal Foundation in San Diego who participated in the research, said the scientists could find “no remaining feasible alternative causes” for the lesions except petroleum exposure from the Deepwater Horizon spill.
BP issued a statement saying the study proved no connection between the disaster and the dolphin die-off, which actually began several months before the oil spill. The National Oceanic and Atmospheric Administration lists the die-off as having started in February 2010, while the spill was in April.
“Correlation is not evidence of causation,” wrote BP spokesman Geoff Morrell.
The paper published Wednesday follows previous studies suggesting a connection between the oil spill and a dolphin die-off in the gulf. In 2013, scientists with NOAA published a paper showing that living dolphins in Barataria Bay, La., showed severe lung diseases associated with oil contamination.
In April 2010, an explosion occurred on the Deepwater Horizon drilling rig about 40 miles off the Louisiana coast, after a blowout of a well 5,000 feet below the ocean surface. BP was a majority owner of the well. Over 87 days, oil slicks spread across open water and fouled more than 1,000 miles of coastline. It was the worst offshore oil spill in U.S. history.
The study is part of a process led by NOAA called Deepwater Horizon Natural Resource Damage Assessment. If studies find a link between the spill and any damage, BP will be expected to pay compensation, though the company can appeal findings in court.
Ms. Colegrove said research on dolphins in the area where the oil spill occurred will continue.
“It really could be many years before we receive the full effects of the oil spill on the dolphin populations,” she said.