Ailing dolphins
Research marks uptick in deaths since BP spill
Diseases may be linked to 2010 spill, scientists say.
Bottlenose dolphins found within the footprint of the Deepwater Horizon oil spill are displaying unusual and life-threatening diseases consistent with exposure to petroleum products, a team of scientists investigating a spike in deaths said Wednesday.
The latest findings mark an “important piece in the chain of evidence” linking an uptick in deaths since early 2010 to the BP oil rig disaster that spewed millions of gallons of crude oil into the Gulf of Mexico, researchers said.
In the latest study, researchers associated with the National Oceanic and Atmospheric Administration examined tissue samples from 46 dolphin carcasses found in the area affected by the spill. They compared them with samples from 106 carcasses discovered at other times and in other stretches of coast, including Texas and Florida.
They found the dolphins within the boundaries of the spill were more likely to have adrenal and lung lesions consistent with exposure to oil.
“Studies have increasingly pointed to the presence of petroleum hydrocarbons as being the most significant cause of the ill-
nesses and deaths plaguing the Gulf ’s dolphin population,” said Teri Rowles, head of National Oceanic and Atmospheric Administration’s Marine Mammal Health and Stranding Response Program.
But BP was quick to rebut the findings.
Geoff Morrell, BP’s senior vice president for U.S. communications and external affairs, noted that the dolphin die-off started before the April 20, 2010, explosion aboard the Macondo Prospect, which killed 11 people and triggered the largest accidental marine oil spill in history.
“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,” Morrell said. “This new paper fails to show that the illnesses observed in some dolphins were caused by exposure to Macondo oil.”
Morrell said though the deaths “may have overlapped in some areas with the oil spill, correlation is not evidence of causation.”
The government declared the “unusual mortality event” for the Gulf dolphins and whales months prior to the spill — in February 2010 — after seeing greater numbers of them stranded along the Gulf coast. Since then, the government has counted 1,395 stranded whales and dolphins. Only 6 percent of them were still alive.
The latest government study paints a grim picture of the health of bottlenose dolphins in portions of the Gulf, primarily in Louisiana, Mississippi and Alabama.
A third of the dolphin carcasses examined there had a thin or damaged adrenal cortex, which can affect production of key hormones that help regulate metabolism and stress responses. That compares with about 7 percent in the control group of other dolphins.
“Animals with untreated adrenal dysfunction can essentially be balancing precariously on a ledge, waiting for the right stressor to push them into an adrenal crisis, including rapid death from shock,” said Stephanie Venn-Watson, the lead author on the latest study, published Wednesday in the online journal PLOS ONE.
In addition to the adrenal lesions, NOAA’s scientific team discovered that more than one in five dolphins that died within the spill boundaries had bacterial pneumonia. Many of these cases were “unusual in severity, and caused or contributed to death,” they found.
But BP’s Morrell said numerous studies conducted over the last several decades have shown that respiratory illness — one of the conditions cited — is among the most common causes of death for bottlenose dolphins.
Kathleen Colegrove, a veterinary pathologist at the University of Illinois who contributed to the study, said the dolphins had some of the most severe lung lesions she’d seen in more than 13 years of examining dead dolphin tissues across the United States.
Dolphins have a particularly high risk of chemical inhalation because their lungs are large and they take big, deep breaths at the water’s surface, and hold their breath for extended periods of time, Venn-Watson said.
NOAA scientists said they explored potential causes besides the oil spill — including Brucella bacteria and morbillivirus infections — but found their prevalence was no different than dolphins outside the spill area or time frame.