More than 260 dolphins found stranded along the Gulf Coast since February. Scientists aren't sure why.

N'dea Yancey-Bragg

Scientists are trying to determine why more than 260 bottlenose dolphins have been found stranded along the Northern Gulf of Mexico since the beginning of February.

The number of dolphin deaths is about three times higher than the average for the time period, researchers from the National Oceanic and Atmospheric Administration said Friday.

The strandings in Louisiana, Mississippi, Alabama and the panhandle of Florida have been declared an Unusual Mortality Event, or UME.

A UME is defined under the Marine Mammal Protection Act as "a stranding that is unexpected; involves a significant die-off of any marine mammal population; and demands immediate response."

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Researchers said it is too early to discern the cause of the deaths because many of the dolphins recovered are very decomposed, making it harder to determine why they died. Some carcasses have been stranded in remote locations, which made it difficult for scientists to recover or examine them.  

Some of the stranded dolphins had skin lesions associated with freshwater exposure, which is being investigated as a possible contributing factor, NOAA researchers said. In addition to skin lesions, dolphins can suffer from abnormal blood chemistry, swelling of the cornea and even death if they are exposed to low salinity water for an extended time.

Researchers said high levels of rainfall and flood control actions have altered the flow of freshwater in dolphin habitats this year. Dolphins in the area also suffered health problems after the Deepwater Horizon oil spill in 2010 that may make them more susceptible to the effects of low salinity.

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The BP oil spill's effects included problems with lungs and adrenal glands, which produce stress-related hormones, blood abnormalities and general poor condition, according to earlier reports. The report said the spill contributed to the Gulf of Mexico’s largest and longest dolphin die-off.

An investigative team will work with the Working Group on Marine Mammal Unusual Mortality Events to evaluate the situation and guide the investigation, which may take months, NOAA said.

Scientists asked members of the public who encounter stranded or dead dolphins to keep a safe distance and call the Southeast Marine Mammal Stranding Hotline at 877-WHALE HELP (877-942-5343), or notify the U.S. Coast Guard.

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Contributing: The Associated Press

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This article originally appeared on USA TODAY: More than 260 dolphins found stranded along the Gulf Coast since February. Scientists aren't sure why.