Dolphins living in Louisiana’s Barataria Bay still struggle to reproduce seven years after an explosion on the Deepwater Horizon oil drilling platform.

Scientists are still investigating the effects of the disaster on the Gulf ecosystem. Much of this research has not yet been made public, as it is part of the federal government’s case against BP and the other companies responsible for the disaster.

As top-level predators, bottlenose dolphins play an important role in the Gulf ecosystem. Gulf bottlenose dolphins include coastal populations that migrate into bays, estuaries and river mouths, as well as offshore populations that live in the open sea along the continental shelf.

Since the spill began, approximately 1,000 bottlenose dolphins have been found dead in an area stretching from the Florida panhandle to the Texas-Louisiana border.

In 2014, dolphins were found dead at more than twice historic rates in this area. However, these deaths were not evenly distributed—places that received less oil did not have particularly elevated numbers of dolphin deaths in 2014, while dolphins in heavilyoiled Louisiana were found dead at four times historic rates.

A study conducted in 2011 found that dolphins in Louisiana’s Barataria Bay had symptoms consistent with oil exposure—such as unusual lung masses, adrenal problems and tooth loss. Nearly half the

dolphins examined were very ill; 17 percent of the dolphins were not expected to survive. The study also concluded that the health effects would likely reduce the dolphins’ ability to reproduce.

A more recent, separate study found that dead dolphins were recovered in larger numbers in heavily oiled places such as Barataria Bay.

This study also found that the deaths of a cluster of dolphins during the months before the Deepwater Horizon exploded were likely caused by extended exposure to fresh water and unusually cold weather.

This is by far the longest period of above-average deaths in the past two decades and it includes the greatest number of stranded dolphins ever found in the Gulf of Mexico.

NOAA has determined that there is no evidence that the two most common causes of previous dolphin deaths—morbillivirus and red tide—are a factor in the current mortalities.


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