Bottlenose dolphins are stranding themselves at an unusually high rate in the northern Gulf of Mexico, including Louisiana, Mississippi, Alabama and the Florida panhandle.

Authorities say more than 260 dolphins have stranded along the U.S. Gulf Coast since Feb. 1, triple the usual number. Scientists from the National Oceanic and Atmospheric Administration (NOAA) say 98% of those dolphins died, and they've classified the strandings as "unusual mortality events."

Unusual mortality events are defined as "a stranding that is unexpected; involves a significant die-off of any marine mammal population; and demands immediate response."

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Scientists say it's too early to know the cause, but they're investigating whether lingering effects from the 2010 Deepwater Horizon oil spill and salinity changes from high rivers and a Louisiana spillway opening contributed.

NOAA says on its website that a number of the dolphins stranded from Louisiana to the Florida Panhandle had sores consistent with freshwater exposure, but those are common in the spring.

A Mississippi scientist says the spillway opening is at least partly to blame for 126 dolphin deaths across Mississippi's coastline. Moby Solangi calls it worse than the BP spill. He says 91 dead dolphins were found in Mississippi during all of 2010.