Diseased lungs and adrenal glands found in dead dolphins on northern Gulf of Mexico beaches are evidence of petroleum contamination, and show the 2010-2012 die-off was linked to the Deepwater Horizon oil spill, researchers reported.
“We found dolphins dying after the oil spill had distinct lung and adrenal gland lesions…These dolphins had some of the most severe lung lesions I’ve seen,” said Dr. Kathleen Colegrove of the University of Illinois, the lead veterinary pathologist on the study sponsored by the National Oceanic and Atmospheric Administration.
The adrenal gland produces hormones to regulate body functions, and dolphin remains examined in the study had 10 times the rate of adrenal damage usually found in stranding cases, Colegrove said.
As air-breathing mammals, dolphins are especially susceptible to poisoning from oil, said Dr. Stephanie Venn-Watson, the study’s lead author and veterinary epidemiologist at the National Marine Mammal Foundation.
“They take great big breaths at the ocean surface, and hold it for a long time,” Venn-Watson said. That exposes their lungs directly to oil floating on the surface.
“No other feasible causes remain” to explain the deaths, she said.
The die-off – technically called an “unusual mortality event” by the National Oceanic and Atmospheric Administration – was investigated as part of NOAA’s ongoing natural resources damage assessment in the five years since the Deepwater Horizon disaster.
Still underway is a similar examination of what killed stranded sea turtles that washed up during and after the spill. Almost 1,000 turtles were found in the months after the Macondo well blowout.
Some NOAA officials and environmental groups suggested turtles were killed in fishing nets by fishermen not using agency-mandated turtle excluders on their gear. Industry advocates called that a whitewash, citing NOAA reports that showed stranding peaking early at the height of the spill as shrimpers remained tied up across the Gulf region.