The peer reviewed 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. 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.
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 causes of the Northern Gulf UME are still under investigation. You can review the full study here.
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.