Deepwater Horizon oil spill contributed to
high number of Gulf dolphin deaths
Tissue study finds petroleum contaminants likely cause
of lung, adrenal lesions causing stranding deaths
SAN DIEGO -- A team of scientists, led by National Marine Mammal Foundation’s Dr. Stephanie Venn-Watson, has discovered that stranded and dead bottlenose dolphins in the northern Gulf of Mexico since the Deepwater Horizon (DWH) oil spill have lung and adrenal lesions consistent with petroleum product exposure. These findings published today in PLOS ONE support a previous health assessment of live dolphins in Barataria Bay, Louisiana during 2011 with NMMF’s Executive Director, Dr. Cynthia Smith, which showed that dolphins had poor health, adrenal disease, and lung disease. The current findings have been part of an ongoing investigation of an Unusual Mortality Event in the northern Gulf of Mexico.
The timing, location, and nature of the detected lesions support that contaminants from the DWH oil spill caused these lesions and contributed to the high numbers of dolphin deaths within this oil spill’s footprint. Increased dolphin deaths following the DWH oil spill has been part of a northern Gulf of Mexico unusual mortality event.
Barataria Bay, Louisiana was one of the most heavily oiled coastal areas from the Deepwater Horizon oil spill, and the new study shows that half of the dead dolphins in Barataria Bay that stranded between June 2010 and November 2012 had a thin adrenal gland cortex, an indicator of adrenal insufficiency. One in every three dolphins across Louisiana, Mississippi and Alabama had this lesion. In comparison, only 7 percent of reference dolphins that stranded outside the location of or before the Deepwater Horizon oil spill had a thin adrenal cortex.
Animals with untreated adrenal insufficiency are at risk of life-threatening adrenal crises. The adrenal gland produces hormones – such as cortisol and aldosterone – that regulate metabolism, blood pressure and other bodily functions. The risk of death from this condition increases when animals are challenged with pregnancy, cold temperatures, and infections.
“Animals with adrenal insufficiency are less able to cope with additional stressors in their everyday lives,” said Dr. Stephanie Venn-Watson, the study’s lead author and veterinary epidemiologist at the National Marine Mammal Foundation, “and when those stressors occur, they are more likely to die.”
In fact, almost half of the dolphins with this otherwise rare adrenal lesion appeared to have died without another clear explanation for their death.
See the complete PLOS ONE article here.
In addition to the adrenal lesions, the scientific team discovered that more than one in five dolphins that died within the DWH oil spill footprint had a primary bacterial pneumonia. Many of these cases were unusual in severity, and caused or contributed to death.
“These dolphins had some of the most severe lung lesions I have seen in the over 13 years that I have been looking dead dolphin tissues from throughout the U.S.,” said Dr. Kathleen Colegrove, the study’s lead veterinary pathologist based at the University of Illinois. In comparison, only 2 percent of reference dolphins had this lesion.
In other mammals, exposure to petroleum compounds through inhalation or aspiration of oil products can lead to injured lungs and altered immune function, both of which can increase an animals’ susceptibility to primary bacterial pneumonia. Dolphins are particularly susceptible to inhalation effects due to their large lungs, deep breaths, and extended breath hold times.
“This is the latest in a series of peer-reviewed scientific studies conducted over the five years since the spill looking at possible reasons for the historically high number of dolphin deaths that have occurred within the footprint of the DWH spill,” said Teri Rowles, Ph.D., one of 22 contributing authors on the paper, and head of NOAA’s Marine Mammal Health and Stranding Response Program, which is charged with determining the causes of UMEs. “These studies have increasingly pointed to the presence of petroleum hydrocarbons as being the most significant cause of the illnesses and deaths plaguing the Gulf’s dolphin population. This study carries those findings significantly forward.”
Since early 2010, there has been an ongoing cetacean unusual mortality event involving primarily bottlenose dolphins in the northern Gulf of Mexico
. Three out of four groupings of elevated dolphin strandings identified within this event followed the Deepwater Horizon oil spill. This die-off, with the highest number of dead bottlenose dolphin strandings on record in the northern Gulf of Mexico, coincides with the the largest marine-based oil spill in the U.S.
Direct causes of death during this period likely included:
1) Chronic adrenal insufficiency resulting from adrenal gland effects;
2) Increased susceptibility to life-threatening adrenal crises, especially when challenged with pregnancy, cold temperatures, and infections; and
3) Increased susceptibility to primary bacterial pneumonia, possibly due to inhalation injury, aspiration of oil spill related products, or alterations in immune function.
The prevalence of Brucella and morbillivirus infections, which were alternative causes for increased dolphin deaths, was low in post-DWH oil spill dolphins and no different compared to the reference dolphins. Additionally, biotoxin levels were either low or below the detection limit in cases.
Ongoing studies assessing changes in these lung and adrenal gland lesions over time will help to address questions regarding how long these chronic conditions may last.
The study team included representatives from: NOAA’s National Marine Fisheries Service; NOAA’s National Ocean Service, the National Marine Mammal Foundation, the University of Illinois the University of Georgia;; the Dauphin Island Sea Lab and University of South Alabama; the Institute for Marine Mammal Studies, Gulfport, Mississippi; the Louisiana Department of Wildlife and Fisheries; the Audubon Aquarium of the Americas, New Orleans; the Mote Marine Laboratory, Sarasota, Florida; the Texas Marine Mammal Stranding Network, Galveston; and the Marine Mammal Pathology Services, Olney, Maryland.
This work was completed as a part of the Northern Gulf of Mexico Unusual Mortality Event Investigation and a part of the Deepwater Horizon Natural Resource Damage Assessment being conducted cooperatively among NOAA, other Federal and State Trustees, and BP.
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Photo credit: NOAA.
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The National Marine Mammal Foundation is a non-profit organization with the mission to improve marine mammal and human health through research, conservation and education. More about the National Marine Mammal Foundation can be found at www.NMMF.org