Associated Press

Unusually cold water in the Gulf of Mexico combined with damage to the food web from the BP oil spill probably caused the premature deaths of hundreds of dolphins in the region, a new report concludes.

The study, published in the journal PLoS One, suggests that a perfect storm of events led to the deaths. The researchers cited three specific stresses: an unusually cold winter in 2010, the oil spill from April to July of 2010 and an unusually large and rapid flow of very cold freshwater from melting snows in January 2011. Such cold water would have been tolerable to healthy dolphins, they suggested, but many of the dolphins in the northern Gulf were unhealthy and had thin blubber layers.

Graham A.J. Worthy, a biologist and contributing author from the University of Central Florida, said the study was not definitively linking the deaths to the oil spill but seeking to assemble the various pieces of the puzzle. “Everything ultimately seems to be linked back to poor body condition,” he said. “So what would cause poor body condition?”

“What we do know was that there was a cold winter in 2010 which might have affected dolphin food resources, and the BP oil spill occurred in 2010, and there is increasing evidence of spill materials entering coastal ecosystems and negatively impacting the food web,” he said.



The report was produced by a team of scientists from half a dozen Southern universities and research institutes, including the Dauphin Island Sea Lab and the University of Central Florida, that have been studying the dolphin deaths for two years.

Whether the oil spill from the Macondo well is related to the unusually high number of dolphin deaths in the northern gulf has been an enduring mystery.

At least 754 dolphins have been reported stranded there since February 2010. The dolphin deaths have mostly ceased in Florida, which was further from the spill site, but have continued in Alabama, Louisiana and Mississippi. In January 2011, there was also a spike in the deaths of baby dolphins.

So far the National Oceanic and Atmospheric Administration has stopped short of linking the dolphin deaths directly to the spill. But in March the agency released a report on autopsies on 32 dolphins from Barataria Bay off Louisiana, which was hit hard by the spill.

The necropsies showed that the dolphins had low amounts of a stress hormone, indicating adrenal insufficiency, which has been associated with oil contamination among mammals in other studies.

Teri Rowles, the coordinator of the National Marine Mammal Health and Stranding Response Program at NOAA’s Fisheries Service, said the agency would review the paper but had yet to come to any conclusion about the role of the oil spill in dolphin deaths. “We are still evaluating contributing factors and causes of this event,” she said.