BILOXI -- The increased number of stillborn and juvenile dolphins found beached along the Gulf of Mexico from 2010 to 2013 was likely caused by chronic illnesses in mothers who were exposed to oil from the Deepwater Horizon spill, scientists said Tuesday.
A paper published in the journal Diseases of Aquatic Organisms is part of an effort to explain the unusually high mortality in the Gulf involving bottlenose dolphins, from early 2010 into 2014.
The investigations into both the deaths of dolphin fetuses and the overall the effects of the oil spill are continuing, the National Oceanic and Atmospheric Administration said Tuesday in a press release. The long-term effects of the spill on dolphin reproduction are still unknown.
Bottlenose dolphins have been dying in record numbers in their mothers' wombs or shortly after birth in areas affected by the 2010 oil spill, according to NOAA.
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"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," said veterinarian Dr. Teri Rowles, co-author on the study, and head of NOAA's Marine Mammal Health and Stranding Response Program, which is charged with determining the causes of these events.
"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," said Kathleen Colegrove, Ph.D., the study's lead author and veterinary pathology professor at the University of Illinois Chicago-based Zoological Pathology Program.
Scientists saw more stranded stillborn and baby dolphins in the spill zone, particularly in Mississippi and Alabama, in 2011 than in other years.
"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," said Dr. Stephanie Venn-Watson, study co-author and veterinary epidemiologist from the National Marine Mammal Foundation.
Bottlenose dolphins are pregnant for a little more than a year, so stillborn and baby 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," Colegrove said.
The researchers report 88 percent of the stillborn and baby dolphins found in the spill zone had abnormal lungs, including partially or completely collapsed lungs. That and their small size suggest 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 baby dolphins found in areas unaffected by the spill had this lung abnormality, the researchers said.
A previous study from Venn-Watson and Colegrove revealed non-perinatal bottlenose dolphins that stranded in the spill zone after the spill were much more likely than other stranded dolphins to have severe lung and adrenal gland damage "consistent with petroleum product exposure."
The study team included researchers from the University of Illinois; National Marine Mammal Foundation; NOAA; the Dauphin Island Sea Lab and University of South Alabama; the Institute for Marine Mammal Studies in Gulfport; the Louisiana Department of Wildlife and Fisheries; Animal Health Center in British Columbia; the Mote Marine Laboratory in Florida; the University of Georgia; and the University of North Carolina.
The study was conducted in conjunction with the Natural Resource Damage Assessment for the Deepwater Horizon spill, as well as the investigation into the northern Gulf of Mexico unusual mortality event. These results are included in the injury assessment documented in the Programmatic Damage Assessment and Restoration Plan. The marine mammal findings are found between pages 4-584 and 4-647. The restoration types laid out in the plan will address injuries to dolphins due to the oil spill.