You Wouldn’t in a Million Years Believe What’s Killing Off Dolphins

May 26, 2015 by


Bottlenose dolphins in the northern Gulf of Mexico have been dying at unusually high rates since 2010. Can you guess why?

NEW ORLEANS (CN) – Lung and adrenal lesions in dolphins, and an increase in bottlenose dolphin deaths in the Gulf of Mexico, is likely linked to exposure to pollutants from the Deepwater Horizon oil spill, according to researchers by the National Oceanic and Atmospheric Association.

According to a report published Wednesday in the peer-reviewed online journal PLOS ONE, bottlenose dolphins in the northern Gulf of Mexico have been dying at unusually high rates since 2010.

This ongoing die-off includes the highest number of bottlenose dolphin deaths on record and coincided – not coincidentally, according to the study – with the largest offshore oil spill in U.S. history.

A team of scientists studied 46 dead bottlenose dolphins found along the Gulf Coast between June 2010 and December 2012 and concluded the lung and adrenal lesions in the dolphins are consistent with exposure to oil and oil-related products in the Gulf of Mexico following an oil spill.

“This is the latest in a series of peer-reviewed scientific studies, conducted over a period of 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 Deepwater Horizon spill,” Dr. Terri Rowles, head of NOAA’s Marine Mammal and Stranding Response Program, said in a statement.

“These studies have increasingly pointed to the presence of petroleum hydrocarbons as being the most significant cause of illnesses and deaths plaguing the Gulf’s dolphin population,” Rowles said. “This study carries those findings significantly forward.”

The timing, location and nature of the detected lesions support the scientists’ finding that contaminants from the Deepwater Horizon oil spill are responsible for a spike in dolphin deaths in the Gulf of Mexico following the oil spill.

Direct cause of death in dolphins likely included chronic adrenal insufficiency resulting from adrenal gland effects, according to the study.

The adrenal gland produces hormones – such as cortisol and aldosterone – that regulate metabolism, blood pressure and other bodily functions.

“Animals with adrenal insufficiency are less able to cope with additional stressors in their everyday lives,” Dr. Stephanie Venn-Watson, lead author of the study and veterinary epidemiologist at the National Marine Mammal Foundation, said. “And when those stressors occur, they are more likely to die.”

The findings support a study of live dolphins in Barataria Bay, Louisiana, an area which was heavily oiled during the oil spill, and which showed the resident dolphins had poor health, adrenal and lung diseases, especially when compared with live dolphins in areas less affected by the oil spill.

Half of the dead dolphins found near heavily oiled Barataria Bay between 2010 and 2012 had a thin adrenal gland cortex, indicative of adrenal insufficiency, the study found.

One in every three dolphins found across Louisiana, Mississippi and Alabama had the legion. In comparison, just seven percent of dead dolphins collected outside of the affected area had the legion, the report said.

Additionally, almost half of the dolphins found with this rare abnormality appeared to have died for no other discernible reason, the study found.

And more than one in five dolphins that died within the footprint of the Deepwater Horizon oil spill had a primarily bacterial ammonia. Many cases of which were uncommonly severe and either caused or contributed to the dolphin’s death.

“These dolphins had some of the most severe lung lesions I have ever seen in the over 13 years that I have been examining dead dolphin tissues from throughout the United States,” Dr. Kathleen Colegrove, the study’s lead veterinary pathologist based at the University of Illinois said in a statement.

In all mammals, inhalation of petroleum-based products can lead to damaged lungs, but dolphins are particularly susceptible to such harm because of their large lungs, deep breaths and extended breath hold times.

BP, who owned the Macondo well that spewed millions of gallons of oil into the Gulf of Mexico following the April 20, 2010 explosion of the Deepwater Horizon, was unsatisfied with the results of the study and issued a statement.

“The data we have seen thus far, including the new study from NOAA, do not show that oil from the Deepwater Horizon accident caused an increase in dolphin mortality. … Based on a review of available literature, we are unaware of any toxicological studies linking lung disease in bottlenose dolphins to exposure to oil or other environmental contaminants,” the oil giant said.

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