Between 2010 and 2014, more than a thousand common bottle-nosed dolphins washed ashore on the coast of the Gulf of Mexico.

These dolphin strandings were the “largest and longest cetacean unusual mortality event” ever recorded in the Gulf of Mexico, scientists found in a previous study. A large proportion of the dead dolphins were perinates — late-term dolphins that had died inside the womb or very young newborns.

Now, experts say that the unusually high mortality of these perinates may be associated with the 2010 Deepwater Horizon oil spill. Exposure to the oil spill could have caused late-term abortions of the in-utero dolphins, or early death of the newborns, researchers conclude in a new paper published in Diseases of Aquatic Organisms.

Previous studies have linked the oil spill to health abnormalities in dolphins. A study published last year, for example, found that exposure to oil spill had possibly caused lung diseases and other health problems in dolphins in Louisiana in the Gulf of Mexico. These dolphins were unable to produce viable calves, the team found, suggesting that the oil spill may have caused failed pregnancies.

The BP oil spill began in April 2010. To find out whether dolphin strandings on the Gulf of Mexico were linked to the oil spill, a team of researchers examined 69 baby dolphins that had washed ashore on the Gulf of Mexico between 2009 and 2013, and compared them to a control population of 26 dolphins that had stranded in South Carolina and Florida, outside the oil spill area.

The team found that in comparison to the reference dolphins, the Gulf of Mexico bottlenose dolphins seemed to be at greater risk of late term pregnancy failures, signs of fetal distress and development of in utero infections including brucellosis.

Moreover, 88 percent of the dolphins that had washed ashore in the oil spill zones had lung abnormalities, including partially or completely collapsed lungs, the study found. In contrast, only 15 percent of the control dolphins had lung abnormalities.

Bottlenose dolphins are typically pregnant for about 380 days, experts say. Since most number of dolphin strandings occurred in 2011, particularly in Mississippi and Alabama, the scientists speculate that the baby dolphins found dead in 2011 could have been exposed in the womb to petroleum products released in 2010.

“Pregnant dolphins losing fetuses in 2011 would have been in the earlier stages of pregnancy in 2010 during the oil spill,” Kathleen Colegrove, the study’s lead author and veterinary pathology professor at the University of Illinois Chicago-based Zoological Pathology Program, said in a statement.

Veterinarian Teri Rowles, co-author on the study, and head of NOAA’s Marine Mammal Health and Stranding Response Program, added, “Our new findings add to the mounting evidence from peer-reviewed studies that exposure to petroleum compounds following the Deepwater Horizon oil spill severely harmed the reproductive health of dolphins living in the oil spill footprint in the northern Gulf of Mexico.”


  • Colegrove, et al. 2016 Fetal distress and in utero pneumonia in perinatal dolphins during the Northern Gulf of Mexico unusual mortality event. Diseases of Aquatic Organisms. 119: 1–16. doi: 10.3354/dao02969