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By Letitia Stein
TAMPA, Fla., May 20 (Reuters) - A record dolphin die-off inthe northern Gulf of Mexico was caused by the largest oil spillin U.S. history, researchers said on Wednesday, citing a newstudy that found many of the dolphins died with rare lesionslinked to petroleum exposure.
Scientists said the study of dead dolphins tissue roundedout the research into a spike of dolphin deaths in the regionaffected by BP Plc's oil spill that was caused by the2010 Deepwater Horizon oil rig explosion.
Millions of barrels of crude oil spewed into Gulf waters,and a dolphin die-off was subsequently seen around coastalLouisiana, Alabama and Mississippi, according to the NationalOceanic and Atmospheric Administration (NOAA).
"Dolphins were negatively impacted by exposure to petroleumcompounds," from the spill, said Stephanie Venn-Watson, aveterinary epidemiologist at the National Marine MammalFoundation and lead author of the study published in thescientific journal PLOS ONE.
"Exposure to these compounds caused life-threatening adrenaland lung disease that has contributed to the increase of dolphindeaths in the northern Gulf of Mexico," she added.
More than 1,200 cetacean marine mammals, mostly bottlenosedolphins, have been found beached or stranded since the spill,according to NOAA, which has declared an ongoing "unusualmortality event" under 1972 Marine Mammal Protection Act.
To understand the cause of death, researchers comparedtissue samples from 46 dolphins in areas affected by the spillwith 106 dolphins that were not exposed.
One-third of the oil-exposed dolphins suffered rare adrenaldamage, consistent with petroleum exposure, the study found.
Yet only seven percent of the dolphins away from the spillhad similar adrenal disease, which would hurt their ability toproduce critical hormones and make them vulnerable to stressors,researchers said.
Dead dolphins near the spill were more likely to have lungdamage and pneumonia, researchers found, explaining the mammalswould have inhaled contaminants coming up for air near thewater's surface.
"These dolphins had some of the most severe lung lesions Ihave ever seen in wild dolphins throughout the United States,"said Kathleen Colegrove, the University of Illinois-based leadveterinary pathologist for the study.
Yet BP questioned whether other factors were to blame.
"The data we have seen thus far, including the new studyfrom NOAA, do not show that oil from the Deepwater Horizonaccident caused an increase in dolphin mortality," said GeoffMorrell, BP's senior vice president for U.S. communications, ina statement. (Reporting by Letitia Stein; Editing by Marguerita Choy)
