Hundreds of dolphins have been found dead along the American Gulf Coast in recent months – an event so strange that it has been described as an "unusual mortality phenomenon" by the National Atmospheric Oceanic Administration.
More than 261 bottlenose dolphins have been stranded in Louisiana, Mississippi, Alabama and the Florida Panhandle, officials said Friday. The number is about three times higher than the average.
At least 60 seals have been reported dead in Alaska, officials say
NOAA determined that the collective deaths constituted an "unusual mortality event", defined as "an unexpected stranding, resulting in the significant death of any population of marine mammals and requiring an immediate response".
Many of the recovered dolphin carcasses "are highly decomposed," officials said. This limits "the ability to collect samples to determine the cause of illness or death".
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According to NOAA, "grounding" occurs when a marine mammal or sea turtle is found dead on the beach or floating near the shore, or if the creatures are alive near the shore but can not return to sea by on their own or because they need help.
Scientists are investigating the possibility that the lingering effects of BP's oil spill in 2010 may be behind the unusually high death toll for dolphins. Problems with the lungs and the adrenal glands, which produce stress-related hormones; blood abnormalities; and the poor general condition, were considered as effects of the oil spill.
Earlier reports have indicated that the spill has contributed to the decline of the largest and longest dolphin in the Gulf of Mexico.
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"We know that some health conditions … are improving, but some have been slow to improve," said Terri Rowles, coordinator of the marine mammal health and stranding program. At NOAA Fisheries, Associated Press. "Breeding in the most heavily oiled areas continues below normal."
Rowles added that scientists would also investigate whether the more immediate effects of low salinity due to the presence of freshwater in high rivers and a spillway in Louisiana had contributed to the deaths.
Associated Press contributed to this report.