Dolphins in an area of the Gulf of Mexico hard hit by the Deepwater Horizon oil spill were five times more likely than other dolphins to have moderate to severe lung diseases and uncommon hormone abnormalities.  (Credit: Visit St. Pete-Clearwater/Flickr)

Dolphins near Deepwater oil spill are still sick

Evidence continues to link the 2010 Deepwater Horizon oil spill to an increase in the number of sick dolphins in a region of the Gulf of Mexico that received heavy and prolonged oil exposure.

Researchers tested approximately 30 bottlenose dolphins in Louisiana’s Barataria Bay and found nearly half in “guarded or worse” condition, including 17 percent that were not expected to survive.

Compared to dolphins tested in Florida’s Sarasota Bay, a control site where no oil was observed, Barataria Bay dolphins were five times more likely to have moderate to severe lung diseases and suffer uncommon hormonal abnormalities.

Researchers conducting the hormone tests were unaware of the origin of the dolphins included in the study.

“We observed uncommon disease conditions in Barataria Bay dolphins consistent with petroleum hydrocarbon exposure,” says Ned Place, associate professor at Cornell University’s College of Veterinary Medicine and director of the endocrinology laboratory in the Animal Health Diagnostic Center.

“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.”

Low levels of cortisol

Barataria Bay dolphins tested in 2011 had 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.

For the study, published in Environmental Science & Technology, researchers conducted hormonal analyses on samples collected by a group of scientists and veterinarians led by Lori Schwacke, a scientist at the National Oceanic and Atmospheric Administration and the paper’s first author.

Schwacke had previously evaluated hormone concentrations in different dolphin populations prior to the Deepwater Horizon spill, and these studies established the minimum level of cortisol in unaffected dolphins.

Forty-four percent of dolphins from Barataria Bay sampled in 2011 after the spill had a cortisol concentration that was below the established minimum level. All samples from Sarasota Bay dolphins had values above the minimum.

Stressed out dolphins

“These results strengthen the argument that the relationship is potentially causative rather than just correlative,” Place says. “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 April 2010 explosion at BP’s Deepwater Horizon rig about 40 miles off Louisiana’s coast spewed oil slicks across 68,000 miles of open water and more than 1,000 miles of coastline.

The study, part of NOAA’s Natural Resources Damage Assessment (NRDA), a suite of impact studies in response to the spill, was funded by BP from funds it agreed to give for NRDA studies, but BP was not involved in analysis.

According to a statement BP released in December, NOAA “still has not provided BP with any data demonstrating that the alleged poor health of any dolphins was caused by oil exposure.”

Cornell continues to test dolphin samples that were collected in 2013 and sent by NOAA as part of the ongoing NRDA.

Source: Cornell University

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