Almost half of the dolphins examined during a 2011 post-Deepwater Horizon oil-disaster survey in Barataria Bay were found to be in bad health, and all indications point to oil exposure as the cause, according to a report from the National Oceanic and Atmospheric Administration.
NOAA’s study, which has been peer-reviewed and is to be published in Environment Science and Technology, shows the results from the 2011 examination of about 30 dolphins sampled in Barataria Bay, an area heavily impacted by oil after the 2010 disaster. Those results were compared with dolphins sampled in Sarasota Bay, Fla., which didn’t receive oil, and the contrast was striking.
Almost half of the dolphins in Barataria Bay were found to be in bad health, with some determined to be so sick that they were likely going to die soon.
“We just haven’t seen animals that were in such bad shape as we saw in Barataria Bay,” said Lori Schwacke, co-lead author of the report and Oceans and Human Health Branch chief with NOAA Centers for Coastal and Ocean Sciences.
The health problems in the Barataria Bay dolphins included low levels of hormones that help control the animals’ response to stress, something researchers said hasn’t been documented in dolphins before, although it has been seen in other animals.
That is a health issue because these hormones play a role in a number of bodily functions including regulation of blood pressure and in regulating the immune response of the animal. She said researchers couldn’t find any scientific articles that had documented this lack of stress hormones in dolphins before.
“This is fairly unusual,” Schwacke said.
The examinations also revealed that Barataria Bay dolphins were five times more likely than their counterparts in unoiled areas to have moderate to severe lung disease. In addition, large numbers were underweight.
“What we’re seeing is consistent with oil exposure,” Schwacke said.
In order to rule out other possible causes of the health impacts, researchers looked for possible contamination with other chemicals such as pesticides or flame retardants. However, they found that the Barataria Bay dolphins had lower levels of a wide range of chemicals than the Sarasota dolphins.
“So we feel it’s highly unlikely that the problems we saw were due to other issues,” she said.
Cynthia Smith, co-lead author and executive director and director of medicine with the National Marine Mammal Foundation, said comparisons of major organ health between the two dolphin population also showed major differences. Only one dolphin in the Sarasota group was diagnosed with moderate lung disease, while the ones in Barataria Bay were five times more likely to have a lung disease.
The group did another health assessment project on dolphins in Barataria Bay and Sarasota, expanding to include the Mississippi Sound in Mississippi and Alabama this summer. The results of that assessment are pending. NOAA is also involved in an ongoing study to follow the outcomes of pregnant dolphins found in the 2011 survey to see if there are any impacts on reproductive success, Smith said.
The findings from the 2011 survey come out as an “unusual mortality event” for the north Gulf of Mexico continues for bottlenose dolphins. Starting in February 2010, 1,062 animals have stranded or been reported dead along the coastline, with 913 identified as bottlenose dolphins, said Teri Rowles, co-lead author of the report and coordinator of the NOAA Marine Mammal Health and Stranding Response Program.
“Central Louisiana, including Barataria Bay, has experienced the greatest increase of strandings over the longest period of time,” Rowles said.
Researchers are still looking for the reason so many more dolphins than normal are dying. They say morbillivirus, marine biotoxins like red tide and brucella bacteria don’t appear to be the culprit, as they have been in previous unusual mortality events.
Researchers continue to look for a possible cause. The investigation will also look for any role the oil from the Deepwater Horizon disaster may be playing.