Exposure of cetaceans to petroleum products following the Deepwater Horizon oil spill in the Gulf of Mexico

The Deepwater Horizon (DWH) oil spill was by far the largest offshore oil spill in the history of the USA. For 87 d, the well spilled millions of barrels of oil into the Gulf of Mexico, extensively affecting the habitat of numerous species of cetaceans. Previous studies have suggested that cetaceans would be able to detect and avoid oiled waters and, when in contact, oil would not adhere to their slick skin. However, photographic evidence and field observations gathered following the DWH oil spill documented at least 11 cetacean species swimming through oil and sheen, with oil adhered to their skin. This study not only documented direct exposure of cetaceans to petroleum products but also the persistence of the oil on their skin. In addition, given the extent of the DWH oil spill, the number of affected species and individuals was likely far greater than the documented occurrences captured during this study. Based on this evidence, we suggest that during oil spills in cetacean habitat, direct exposure of whales and dolphins to petroleum products will likely occur and should therefore be taken into account during response activities and damage assessments.