The study on the Gulf’s “unusual mortality event” (UME) reiterates what other experts, such as NOAA, have stated: the UME started three months before the Deepwater Horizon spill, and the cause or causes have not been determined.
The study does not show that the accident adversely impacted dolphin populations.
The researchers suggest that multiple factors likely contributed to the UME, and that these potential causes include cold temperature, freshwater runoff, brucella and the increased public awareness and number of wildlife observers in the Gulf after the spill.
This supports data released by NOAA, which showed that brucella is “a common thread” in a number of the animals examined. Nearly one-third of the dolphins tested through November 2014 tested positive for brucella.
It’s important to note that unfortunately these large die-offs of dolphins aren’t unusual. The study states that there were ten UMEs involving bottlenose dolphins documented in the Gulf prior to 2010. Over the past years there have been dolphin UMEs relating to dolphins all over the world, with no connection to oil spills.
The Barataria Bay health assessment mentioned in the paper failed to establish a link between the observed health of the Barataria Bay dolphins in 2011 and 2013 and potential exposure to oil. It also failed to take into account that Barataria Bay contains numerous stressors that could explain the poor health of some dolphins.