NEW ORLEANS (AP) — In a new study, a team of scientists says there's a definite link between the massive BP oil spill in 2010 and a record number of dolphin deaths along the northern Gulf of Mexico.
The scientists on Wednesday said large numbers of dead bottlenose dolphins found along shores since the spill suffered from lung and adrenal lesions caused by swimming in oil-contaminated seas.
The research paper backs up previous findings linking dolphin deaths to the oil spill. The study involved federal scientists with the National Oceanic and Atmospheric Administration.
BP has rejected the contention linking the deaths to the oil spill. Instead, it said, the dolphins were likely suffering from common respiratory illnesses.
The new study was published Wednesday in the peer-reviewed online journal PLOS ONE.
With the release of the study, researchers and federal government made the most direct link yet between the spill and the dolphin deaths.
"No feasible alternative causes remain that can reasonably explain the timing, location and nature of these distinct lesions and increase in deaths," said Stephanie Venn-Watson, the study's lead researcher with National Marine Mammal Foundation.
From 2002 to 2009, the Gulf averaged 63 dolphin deaths a year. That rose to 125 in the seven months after the spill in 2010 and 335 in all of 2011, averaging more than 200 a year since April 2010.
That's the longest and largest dolphin die-off ever recorded in the Gulf. The number of deaths has started to decline, according to federal scientists.
Researchers said oil contamination caused chronic adrenal problems for dolphins and this in turn hurt their chances of surviving cold temperatures, infections and bacterial pneumonia. Also, the dolphins suffering from oil contamination had problems with pregnancy.
Venn-Watson said dolphins were vulnerable to oil contamination because they take deep breaths at the sea's surface — the same place where oil sheens covered the Gulf following the spill.
"Dolphins were swimming into the oil," she said. "Their lungs are large, they take big deep breaths at the water's surface and hold it for extended periods of time."
The study looked at 46 dead dolphins found in Louisiana, Mississippi and Alabama between June 2010 and December 2012. Researchers tested lung and adrenal gland tissues.
The study looked at 22 dead dolphins found in Barataria Bay, a heavily oiled water body south of New Orleans where researchers first began noticing and tracking dolphin deaths after the spill.
Venn-Watson said further studies would be needed to track and monitor the long-term effects of the contamination on the dolphin populations.
BP questioned the validity of the study because it was based on what it termed "just a small sample set" of dolphins. The company accused the federal government of not releasing in a timely manner hundreds of necropsies.
"This new paper fails to show that the illnesses observed in some dolphins were caused by exposure to Macondo oil," said Geoff Morrell, a BP spokesman.
Morrell said BP was "unaware of any toxicological studies linking lung disease in bottlenose dolphins to exposure to oil or other environmental contaminants."
BP's Macondo well blew out on April 20, 2010, leading to deadly explosions aboard the Deepwater Horizon drilling rig and the nation's largest offshore oil spill.
The federal government used a team of scientists to calculate that about 172 million gallons spilled into the Gulf. BP put the number much lower, closer to 100 million gallons.