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New research has linked the 2010 Deepwater Horizon oil spill to the deterioration of dolphin health in the region of the Gulf of Mexico that received heavy and prolonged oil exposure as a result of the spill.
A study conducted by the National Oceanic and Atmospheric Administration (NOAA) and Cornell University tested approximately 30 bottlenose dolphins in Louisiana's Barataria Bay, revealing the cetaceans to be in less than ideal states of health when compared to dolphins tested at a control site in Florida's Sarasota Bay.
The researchers found half of the dolphins in Louisiana to be in a "guarded or worse" condition, and several of them were not expected to survive. Compared to the control group, the Barataria Bay dolphins were five times more likely to have moderate to severe lung diseases and suffered uncommon hormonal abnormalities.
Cornell University researchers conducted the hormonal tests in 2011, but they were not made aware of the origin of the dolphins included in the study.
"We observed uncommon disease conditions in Barataria Bay dolphins consistent with petroleum hydrocarbon exposure," said Ned Place, an associate professor at Cornell University's College of Veterinary Medicine.
"The Barataria Bay population is loyal to the area, and dolphins could have been exposed to oil by direct contact at the surface or through ingestion while feeding."
The Barataria Bay were found to have "severely low adrenal hormones, including cortisol, which maintains homeostasis and spikes during stress, and aldosterone, which maintains water and salt balance needed for muscle and nerve function," the researchers said in a statement from Cornell.
Of the Barataria Bay dolphins in the hormone sample, 44 percent had a cortisol concentration that was below the established minimum level, the researchers said. The control group all tested at a level above the established minimum.
"These results strengthen the argument that the relationship is potentially causative rather than just correlative," Place said. "Their low cortisol levels were especially pronounced because you'd expect relatively high cortisol levels after the handling involved with capturing dolphins. Such low levels suggest these dolphins have damaged ability to respond to stress, which compromises their survival chances. Dolphins in this area will likely have more difficulty reproducing as well. The severe diseases and associated deaths raise strong concerns for the future of Barataria Bay's dolphin population."
The Deepwater Horizon, an offshore oil rig that that exploded on April 20, 2010, was operated by the oil company BP. The event claimed 11 lives and is considered to be the largest accidental marine oil spill in history.
As part of a settlement, BP was required to fund a NOAA program called the Natural Resources Damage Assessment (NRDA), a suite of impact studies in response to the spill. BP funds were used for the hormone study, but the oil company was not involved in the analysis.
In December, BP stated that NOAA "still has not provided BP with any data demonstrating that the alleged poor health of any dolphins was caused by oil exposure."
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