CHAMPAIGN, Illinois. – Scientists have finalized a five-year study of newborn and fetal dolphins found stranded on beaches in the northern Gulf of Mexico between 2010 and 2013. Their study, reported in the journal Diseases of Aquatic Organisms, identified substantial differences between fetal and newborn dolphins found stranded inside and outside the areas affected by the 2010 Deepwater Horizon oil spill.
The study team evaluated 69 perinatal common bottlenose dolphins in Alabama, Louisiana and Mississippi, the areas most affected by the spill, and 26 others found in areas unaffected by the spill. The work was conducted as part of an effort to investigate an “unusual mortality event” in the Gulf primarily involving bottlenose dolphins, beginning in early 2010 and continuing into 2014.
Scientists saw higher numbers of stranded perinatal dolphins in the spill zone in 2011 than in other years, particularly in Mississippi and Alabama, the researchers report. 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,” they wrote.
Bottlenose dolphin gestation takes about 380 days, so perinatal dolphins that died in the early months of 2011 could have been exposed in the womb to petroleum products released the previous year, said University of Illinois veterinary diagnostic laboratory professor Kathleen Colegrove, who led the study. Colegrove works in the Chicago-based Zoological Pathology Program at the U. of I.
“Dolphin dams losing fetuses in 2011 would have been in the earlier stages of pregnancy in 2010 during the oil spill,” she said.
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 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 those found in areas unaffected by the spill had this lung abnormality, the researchers said.
The team also found that the spill-zone dolphins were “particularly susceptible to late-term pregnancy failures, signs of fetal distress and development of in utero infections including brucellosis,” a bacterial infection that can affect the brain, lungs, bones and reproductive function. Extensive testing found no evidence that an unusual or highly pathogenic Brucella strain was involved.
“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 said.
A previous study by many of the same researchers revealed that nonperinatal bottlenose dolphins 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.”
“These diseases in pregnant dolphins likely led to reproductive losses,” Colegrove said.
“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.
The study team also included researchers from the Animal Health Center in Abbotsford, British Columbia; the Audubon Aquarium of the Americas in New Orleans; the Dauphin Island Sea Lab and the University of South Alabama; the Institute for Marine Mammal Studies in Gulfport, Mississippi; the Louisiana Department of Wildlife and Fisheries; the Mote Marine Laboratory in Sarasota, Florida; the National Marine Mammal Foundation; the National Oceanic and Atmospheric Administration; the University of Georgia; and the University of North Carolina.
To reach Kathleen Colegrove, call 312-585-9050; email firstname.lastname@example.org.
ABSTRACT: An unusual mortality event (UME) involving primarily common bottlenose dolphins Tursiops truncatus of all size classes stranding along coastal Louisiana, Mississippi, and Alabama, USA, started in early 2010 and continued into 2014. During this northern Gulf of Mexico UME, a distinct cluster of perinatal dolphins (total body length <115 cm) stranded in Mississippi and Alabama during 2011. The proportion of annual dolphin strandings that were perinates between 2009 and 2013 were compared to baseline strandings (2000−2005). A case-reference study was conducted to compare demographics, histologic lesions, and Brucella sp. infection prevalence in 69 UME perinatal dolphins to findings from 26 reference perinates stranded in South Carolina and Florida outside of the UME area. Compared to reference perinates, UME perinates were more likely to have died in utero or very soon after birth (presence of atelectasis in 88 vs. 15%, p < 0.0001), have fetal distress (87 vs. 27%, p < 0.0001), and have pneumonia not associated with lungworm infection (65 vs. 19%, p = 0.0001). The percentage of perinates with Brucella sp. infections identified via lung PCR was higher among UME perinates stranding in Mississippi and Alabama compared to reference perinates (61 vs. 24%, p = 0.01), and multiple different Brucella omp genetic sequences were identified in UME perinates. These results support that from 2011 to 2013, during the northern Gulf of Mexico UME, bottlenose dolphins were particularly susceptible to late-term pregnancy failures and development of in utero infections including brucellosis.