The high number of deaths of perinatal (near-birth) dolphins in the Gulf of Mexico was likely caused by exposure to oil from the Deepwater Horizon oil spill. The pregnant dolphins suffered chronic illness caused by exposure to petroleum products which likely contributed to fetal death, according to a team of scientists. Their findings were published today in the journal Diseases of Aquatic Organisms.

The findings add to mounting evidence that exposure to petroleum compounds negatively impacted the reproductive health of dolphins in the oil spill footprint.

The work was conducted as part of an effort to explain the “unusual mortality event” (UME) in the Gulf involving bottlenose dolphins. This study covers the period between early 2010 (the start of the UME) into 2013. The UME investigation, and the investigation into the effects of the oil spill, are ongoing. The long-term effects of the spill on dolphin reproduction are still unknown.

Compared to control populations, the study found Gulf of Mexico bottlenose dolphins were particularly susceptible to:

• late term pregnancy failures
• signs of fetal distress
• development of in utero infections, including brucellosis.

Scientists saw higher numbers of stranded perinatal dolphins in the spill zone in 2011 than in other years, particularly in Mississippi and Alabama. Exposure to oil contributed to significant abnormalities in pregnant dolphin mothers that caused fetal death or death of newborn dolphins shortly after birth.

The young dolphins, which died in the womb or shortly after birth, were significantly smaller than those from previous strandings.

The researchers report that 88 percent of the perinatal dolphins found in the spill zone had lung abnormalities, including partially or completely collapsed lungs. That, combined with their small size, suggests that they died in the womb or very soon after birth—before their lungs could fully inflate.

This study was conducted in conjunction with the Natural Resource Damage Assessment for the Deepwater Horizon oil spill. These results are included in the injury assessment documented in the Programmatic Damage Assessment and Restoration Plan. The restoration types laid out in the plan will address injuries to dolphins due to the oil spill.