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Dolphin Death Spike in Gulf of Mexico Spurs Investigation (1)

June 14, 2019, 7:27 PMUpdated: June 14, 2019, 8:35 PM

U.S. government scientists are investigating whether freshwater flushing through a Mississippi River spillway is contributing to an unusually high number of dolphin deaths in the Gulf of Mexico.

Nearly 280 bottlenose dolphins have been stranded since Feb. 1 along the coast from Louisiana to the Florida Panhandle—three times the usual number, the National Oceanic and Atmospheric Administration said June 14.

All but a handful died, according to NOAA. Mississippi recorded the highest number of strandings, with 121, followed by 87 in Louisiana.

It’s unclear exactly what is killing the dolphins, but NOAA scientists said they were concerned freshwater from extreme flooding farther upstream was contributing to the death toll. Lingering health effects from the 2010 Deepwater Horizon oil spill may also be making the dolphins more vulnerable to environmental changes, such as lower salinity, they said.

Skin Lesions Found

Some dolphins had skin lesions indicating freshwater exposure, said Erin Fougeres, the Southeast regional marine mammal stranding program administrator for NOAA Fisheries.

It’s not uncommon to see dolphins with these lesions in the spring, as freshwater from melting snows or heavy rains and flooding lowers salinity in their habitat in the northern gulf, according to NOAA.

However, a heavier volume of freshwater has been spilling into gulf waters this year, after an extremely wet winter and spring across the central U.S. To reduce pressure on the levees around New Orleans, authorities opened the Bonnet Carre spillway in Louisiana, sending freshwater through Lake Pontchartrain into the Mississippi Sound.

“We are concerned about the low salinity, what could potentially be draining into the water with the low salinity,” Fougeres said in a call with reporters. “We’re also concerned about some of the more indirect impacts to the dolphins, such as alternations in the prey that they might normally be feeding on.”

The agency has declared an unusual mortality event, a designation triggered by unexpected, significant die-offs of marine mammals. Red tide algal blooms and a viral infection have been blamed for other dolphin die-offs along the Gulf Coast since 1991.

The effects of the oil spill were blamed for an unusual mortality event that lasted from March 2010 through July 2014 and killed about 975 bottlenose dolphins, according to NOAA.

(Recasts fourth paragraph to clarify that scientists believe freshwater from extreme flooding farther upstream is most likely cause. )

To contact the reporter on this story: Jennifer Kay in Miami at jkay@bloomberglaw.com

To contact the editors responsible for this story: Gregory Henderson at ghenderson@bloombergenvironment.com; Chuck McCutcheon at cmccutcheon@bloombergenvironment.com