The Deepwater Horizon oil spill caused the bottlenose dolphins (that swim in the affected waters) to die early and give birth to fewer baby dolphins, according to a new study.
Researchers found that in Barataria Bay – a bay of the Gulf of Mexico that was severely affected by the Deepwater Horizon oil spill – only about 20 percent of female dolphins gave birth to calves that survived, compared with 83 percent pregnant dolphins in other dolphin populations.
Moreover, only approximately 86.8 percent of the dolphins in Barataria Bay survive annually, compared with 95.1 percent of dolphins near Charleston, South Carolina, and about 96.2 percent in Sarasota Bay, Florida, according to the researchers.
Lori Schwacke, a wildlife epidemiologist at the National Oceanic and Atmospheric Administration and lead investigator of the study, said that:
“This dolphin population, as well as other dolphin and whale populations that were exposed to the DeepwaterHorizon oil, will take a long time to recover.”
In 2010 April 20, about 205 million gallons of oils leaked into the Gulf of Mexico after the explosion of the Deepwater Horizon oil rig. According to government estimates, it is the worst marine oil spill in the history of the United States.
Researchers have followed the lives of dolphins in that area ever since. In 2011, they conducted a study – published in the journal Environmental Science and Technology – in which they assessed the health of the Barataria Bay dolphins.
The findings showed that the bottlenose dolphins had health issues linked to oil. A lot of dolphins had low blood sugar, were anaemic, presented symptoms of liver disease, and were underweight, the researchers said.
Most of the Barataria Bay dolphins suffered from lung disease, and about half of them had extremely low levels of hormones that help the body respond to stress.
In the new study – published November 4 in the journal Proceedings of the Royal Society B – the researchers monitored 32 dolphins of which 10 were pregnant at the time the study was conducted. The health assessment lasted 47 months (4 years).
The researchers found that the pregnancy success rates of dolphins in the Barataria Bay area were 60 percent lower, than the success rates of dolphins at a reference site.
According to Schwacke, hormonal issues and lung diseases that are associated with oil spill are known to lower the rates of successful pregnancies.
Image Source: ocean.si.edu