The unusual mortality event of several stillborn and juvenile dolphins in the Gulf of Mexico between 2010 and 2014 has been linked to chronic illnesses in mothers who were exposed to oil from the Deepwater Horizon spill.
Led by researchers from the University of Illinois at Urbana-Champaign, the four-year study examined the death of 69 perinatal common bottlenose dolphins in areas most affected by the spill, including Alabama, Louisiana and Mississippi, as well as the death of 26 others found in areas outside the spill zone.
Overall, researchers found substantial differences between fetal and newborn dolphins found stranded on beaches inside and outside the areas, reaffirming the notion that petroleum exposure can have severe side effects on marine life.
For instance, more perinatal dolphins were found stranded in the spill zone in 2011 than any other year - especially along beaches in Mississippi and Alabama.
What's more is young dolphins, who died in the womb or shortly after birth, were much smaller than those stranded in previous years or in areas outside the spill zone.
The gestation period for bottlenose dolphins is about 380 days. Therefore, perinatal dolphins stranded in the early months of 2011 could have been exposed to petroleum products released the previous year while they were still in the womb.
"Dolphin dams losing fetuses in 2011 would have been in the earlier stages of pregnancy in 2010 during the oil spill," explained Kathleen Colegrove, a University of Illinois veterinary diagnostic laboratory professor, who led the study.
Petroleum exposure is also believed to cause lung abnormalities, including partially or completely collapsed lungs. In fact, some 88 percent of dolphins stranded in the spill zone had such abnormalities.
This, combined with unusually small body size, suggests the dolphins died in the womb or very soon after birth, before their lungs were able to fully develop.
Comparatively, researchers found only 15 percent of those stranded in areas unaffected by the spill had such lung abnormalities.
What's worse is many of the dolphins exposed to petroleum suffered late-term pregnancy failures, fetal distress and development of in utero infections including brucellosis - a bacterial infection that can affect the brain, lungs, bones and reproductive function.
"These findings support that pregnant dolphins experienced significant health abnormalities that contributed to increased fetal deaths or deaths of dolphin neonates shortly after birth," Colegrove added. "These diseases in pregnant dolphins likely led to reproductive losses."
Previously, studies have shown that nonperinatal bottlenose dolphins within the Deepwater Horizon spill were more susceptible to severe lung and adrenal gland damage related to petroleum exposure.
"Our new findings add to the mounting evidence from peer-reviewed studies that exposure to petroleum compounds following the Deepwater Horizon oil spill negatively impacted the reproductive health of dolphin populations living in the oil spill footprint in the northern Gulf of Mexico," said Dr. Teri Rowles, a veterinarian with the National Oceanic and Atmospheric Administration's Marine Mammal Health and Stranding Response Program and a co-author on the study.
Their findings were recently published in the journal Diseases of Aquatic Organisms.
