What Scientists Are Currently Telling Us About Dolphins and the Deepwater Horizon Oil Spill


Several studies on bottlenose dolphins have been conducted since the Deepwater Horizon oil spill. Information from these studies to date presents a picture of chronic poor health, failed pregnancies, and increased mortality in the aftermath and footprint of the spill. 

Here are two things you should know about the impact of the oil on Gulf dolphins: 

1) The spill is likely contributing to the largest and longest-lasting dolphin die-off on record in the Gulf of Mexico. 

The dolphin die-off began shortly before the Deepwater Horizon disaster but scientists are seeing adverse health effects in parts of the northern Gulf, such as lung disease, anemia, low body weight and poorly functioning adrenal glands that are consistent with expected effects from oil exposure. Scientists believe these health conditions are likely contributing to the prolonged die-off. 

Annual dolphin deaths reached historic highs in Louisiana, Mississippi, and Alabama after the spill. There have been particularly high numbers of dead perinatal dolphins—dolphins that either died in the womb late in pregnancy or soon after birth. 

A 2011 study looked at dolphins from Barataria Bay, Louisiana, which was heavily oiled after the spill. The Barataria dolphins were five times more likely to have moderate to severe lung disease than a control group in Sarasota Bay, Florida, where oil was not observed. 

As Dr. Lori Schwacke, one of NOAA's lead scientists on the Barataria study put it, "The magnitude of the health effects that we saw was surprising—we've never seen animals that were in this poor condition." 

2) It could be many years before we see the full effects of the oil spill on dolphins. 

Dolphins are a long-lived species that are slow to mature and reproduce. Bottlenose dolphins only reach puberty and begin mating between five and eight years of age. How will the oil spill affect future generations of dolphins? 

We are continuing to track and study live and dead animals as part of the natural resource damage assessment to find out. The results of these studies will also inform and help us determine what needs to be done to restore dolphins.