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Study Provides Possible Clues in Search for Causes of Dolphin Deaths in Gulf of Mexico

Investigators from the Louisiana Department of Wildlife and Fisheries collect data from one of the more than 1,000 dolphins that have stranded in the Northern Gulf of Mexico since spring 2010.  Photo Credit: Courtesy Louisiana Department of Wildlife and Fisheries.

More Information

Investigation Results of the Cetacean Unusual Mortality Event in Northern Gulf of Mexico

February 2015 paper

December 2014 paper (PDF)

December 2013 story

Northern Gulf of Mexico UME

February 11, 2015

A new study has found four distinct groupings of dolphin deaths within the Northern Gulf of Mexico Unusual Mortality Event (UME). Three of the groupings followed the 2010 Deepwater Horizon oil spill. Some of the highest numbers of dolphin deaths occurred in Mississippi, Alabama, and Barataria Bay, Louisiana in 2011. The annual number of dolphin deaths was not elevated for the Gulf coasts of Florida or Texas, which were not as heavily oiled.

The peer reviewed study was conducted in collaboration with marine mammal stranding network organizations across the Gulf region, as well as nationally-recognized marine mammal research institutions and the Working Group for Marine Mammal Unusual Mortality Events. It examined changing characteristics of the UME over time. The scientists compared the number and demographics of dolphin deaths across the Gulf from January 2010–June 2013 to patterns from 1990–2009. They looked for distinct groupings of high numbers of dolphin deaths, both before and after the spill.

"Interestingly, several clusters of dead dolphins identified during this mortality event were consistent with the timing and spatial distribution with the Deepwater Horizon oil spill," said Dr. Stephanie Venn-Watson, the paper’s lead author, veterinarian, and Director of Translational Research at the National Marine Mammal Foundation. "These include the largest, most prolonged cluster in Barataria Bay, followed by those in Mississippi and Alabama during 2011."

The Barataria Bay dolphin population was a focus of previous peer-reviewed study as part of the on-going Deepwater Horizon Natural Resource Damage Assessment (NRDA). That study showed that live dolphins, which underwent physical examination, had adverse health impacts consistent with exposure to petroleum products.

The new study also builds on a recent paper (PDF) that compares this event to 11 past mortality events in the Gulf. That study indicates that the most common causes of previous Gulf events are not likely the cause in this case.

The causes of the Northern Gulf UME are still under investigation. This study indicates that there may be multiple contributing causes and those could vary among the different groupings. Researchers are now comparing diagnostic information, including tissue studies, among these groupings to better understand the potential causes of the deaths—including the role of the oil spill. Additional research findings will likely be published later this year.

This work was part of the Deepwater Horizon Natural Resource Damage Assessment and the Northern Gulf Unusual Mortality Investigation being conducted cooperatively by NOAA, other federal and state agencies, and BP.