Scientists are trying to determine how much the Deepwater Horizon incident has affected the health of bottlenose dolphins in Barataria Bay. To do so they must separate those health issues that might be directly linked to oil exposure during this particular incident from other natural or human caused problems.
A 2013 study reported on the capture and assessment of bottlenose dolphins in the Bay in an attempt to better understand what potential effects of the Deepwater Horizon spill on this population. Their initial findings included many animals with lung and liver damage consistent with exposure to petroleum products, and similar to that reported in humans working oil spill responses and sea otters from the Exxon Valdez oil spill.
However, in early 2010 and before the Deepwater Horizon explosion, the US National Oceanic and Atmospheric Administration (NOAA) began an Unusual Mortality Event (UME) investigation into cetacean strandings within the Gulf of Mexico. Of the more than 1000 whales and dolphin that have been included in the UME, 114 stranded before the response to the Deepwater Horizon began. The vast majority (approximately 830) stranded between November 2010 and December 2013, after the initial oil spill response phase was closed.
Separating effects of oil from other health risks
Thus the researchers must ensure that other potential causes for these increased strandings are examined and either eliminated as a source, or included in the overall assessment. To do so, they have compared results from Barataria Bay with those from dolphins in an area off the Florida coast not affected by the BP oil spill.
In both groups, other contaminants were tested for-PCB, DDT and its derivatives, chlordane, dieldrin, mirex and PBDE (the chemical found in flame retardants that has been linked to heath problems in humans and orca). These contaminants were not found in significant levels in the Barataria dolphins. The photo linked to this article (Credit:NOAA) shows the in-water examination process in Barataria Bay.
Pre-spill data is limited
Another problem in determining the role of the Deepwater Horizon oil spill on these animals is that there is no data on the health of the population prior to the incident. Pre-existing health conditions could be a factor. The health conditions seen in these animals are, as noted above, consistent with petroleum exposure but there are over 54,000 oil wells on and near the Louisiana coast. Reported leaks in the state average 300,000 barrels a year, suggesting that chronic oiling may be playing a role in this dolphin mortality event.
Finding lung and liver damage so long after the spill may also be due in part, to the type of exposure cetaceans experience. These species do not have fur or feathers and rely on their blubber layer for warmth. Thus they would not suffer the hypothermia and inability to swim or fly well that are seen in birds, otters and fur seals, the very effects which often bring these other species into care before long term internal damage has occurred.
While more research is needed, this study may be the first to provide insight into the effects of oil on cetaceans. In previous studies cetaceans were noted to swim through oil and there has been some suggestion that the failure of orca populations in the vicinity of the Exxon Valdez spill to recover may be related to petroleum exposure but direct links between cetacean health and oil spills has not been established. No studies have been completed on those populations, and, as with the Barataria dolphins, there is no pre-spill data on their health. Being able to compare the Barataria dolphins with the Florida animals, who have been monitored for more than 20 years may help in increasing our knowledge.