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Gulf of Mexico dolphin deaths likely due to oil

Study finds higher rate of illness and death in newborns and juvenile bottlenose dolphins after Deepwater Horizon oil spill.

Bottlenose dolphins have been dying in record numbers in their mothers' womb or shortly after birth in areas affected by the 2010 Deepwater Horizon oil spill in the Gulf of Mexico. Photo credit: NOAA

Bottlenose dolphins have been dying in record numbers in their mothers’ womb or shortly after birth in areas affected by the 2010 Deepwater Horizon oil spill in the Gulf of Mexico. Photo credit: NOAA

The increased number of stranded stillborn and juvenile dolphins found in the Gulf of Mexico from 2010 to 2013 were likely caused by chronic illnesses in mothers who were exposed to oil from the Deepwater Horizon spill, scientists said in a NOAA statement today (April 12, 2016).

The new study, published in the journal Diseases of Aquatic Organisms, is part of an effort to explain the unusual mortality event in the Gulf involving bottlenose dolphins between early 2010 and continuing into 2014.

Veterinarian Teri Rowles, co-author on the study, is head of NOAA’s Marine Mammal Health and Stranding Response Program, which is charged with determining the causes of these events. Rowles said:

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 dolphin living in the oil spill footprint in the northern Gulf of Mexico.

A stranded dolphin in March 2013. Young bottlenose dolphins have been dying in areas affected by the 2010 Deepwater Horizon oil spill. Image credit: Louisiana Department of Wildlife and Fisheries

A stranded dolphin in March 2013. Young bottlenose dolphins have been dying in areas affected by the 2010 Deepwater Horizon oil spill. Image credit: Louisiana Department of Wildlife and Fisheries

Dr. Kathleen Colegrove, Ph.D., is the study’s lead author and veterinary pathology professor at the University of Illinois Chicago-based Zoological Pathology Program. She said:

In contrast to control populations, we found that Gulf of Mexico bottlenose dolphins were particularly susceptible to late term pregnancy failures, signs of fetal distress and development of in utero infections including brucellosis.

Scientists saw higher numbers of stranded stillborn and juvenile dolphins in the spill zone in 2011 than in other years, particularly in Mississippi and Alabama.

Dr. Stephanie Venn-Watson is a study co-author and veterinary epidemiologist from the National Marine Mammal Foundation. She said:

The young dolphins, which died in the womb or shortly after birth, were significantly smaller than those that stranded during previous years and in other geographic locations.

Bottlenose dolphins are pregnant for about 380 days, so stillborn and juvenile dolphins found in the early months of 2011 could have been exposed in the womb to petroleum products released the previous year. “Pregnant dolphins losing fetuses in 2011 would have been in the earlier stages of pregnancy in 2010 during the oil spill,” said Colegrove.

The researchers report that 88 percent of the stillborn and juvenile dolphins found in the spill zone had abnormal lung, including partially or completely collapsed lungs. That and their small size suggest that they died in the womb or very soon after birth – before their lungs had a chance to fully inflate. Only 15 percent of stillborn and juvenile dolphins found in areas unaffected by the spill had this lung abnormality, the researchers said.

The investigations into both the fetal dolphin, and the overall the effects of the oil spill, are continuing. The long-term effects of the spill on dolphin reproduction are still unknown.

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Bottom line: A new study published in the journal Diseases of Aquatic Organisms suggests that the increased number of stranded stillborn and juvenile dolphins found in the Gulf of Mexico from 2010 to 2013 were caused by chronic illnesses in mothers who were exposed to oil from the Deepwater Horizon spill.

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Eleanor Imster

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