Dolphins are dying all around Florida and scientists don't know how to stop it.

The die-offs of bottlenose dolphins are going on in three different places, and appear to be from more than one cause. Although dolphins are not an endangered species, the loss of so many all at once is clearly bad news, scientists say.

"This particular species has suffered a huge impact, all over the Southeast," said Blair Mase, a marine mammal specialist with the National Oceanic and Atmospheric Administration, which has classified each of the die-offs as an "unusual mortality event."

Greg Bossart, chief veterinary officer of the Georgia Aquarium, has studied dolphins for more than 30 years and said he can't recall another time when three separate "unusual mortality events" were going on at the same time involving a single species.

What makes so many deaths disturbing, he said, is that dolphins are regarded as "sentinels for ocean and human health," not unlike canaries in a coal mine.

The first sign of trouble came from the Gulf of Mexico. A month before the 2010 Deepwater Horizon oil spill began, dead dolphins began washing ashore along the Gulf Coast.

Then, as the oil spill continued through the summer, the number of dead and dying dolphins increased dramatically, and some began washing ashore on Florida Panhandle beaches as far east as Apalachicola. Some were premature newborns or stillborn dolphins.

A few were coated with oil, and some were suffering from a bacterial infection called Brucella, which scientists believe resulted from the oil suppressing the dolphins' immune system.

As of last Sunday, the total of dead dolphins along the gulf beaches had topped 1,000. The most recent one landed last week on the white sands near Panama City.

Then, beginning last year, dolphins began dying in droves over on Florida's east coast, in the Indian River Lagoon. So far 77 of the 600 that live in the lagoon have died, and only one sick one survived. The survivor, rescued in June and sent to SeaWorld for rehabilitation, was released back to the wild last week.

Hundreds of pelicans and manatees have died in the lagoon too. Scientists are still trying to figure out why, although they suspect it has something to do with the massive blooms of toxic algae that wiped out nearly half of the lagoon's sea grass beds.

The only clue on the dolphins appears to be that although they are emaciated, their stomachs were full of shrimp instead of their usual diet of sea trout, black drum and other fish.

Now comes the latest threat: a morbillivirus, similar to what causes measles in humans and distemper in dogs.

So far it has killed more than 750 dolphins all along the eastern seaboard. The die-off began in the waters off New York and slowly moved southward, shifting to Virginia, then North Carolina, with the numbers dropping in the North and rising in the South.

This month it showed up in a dead dolphin that washed ashore in Florida, near Jacksonville, Mase said. Two more dolphins that stranded themselves in Brevard County may have been victims as well. Tests are going on now to determine whether the virus killed them as well.

So far there is no sign that the morbillivirus has hit the already embattled Indian River Lagoon dolphins, but that's a possibility.

Dolphins along the Atlantic coast are migratory creatures, and when the infected ones surface to breathe, they spread the virus to other dolphins through droplets sprayed out of their blowholes, Bossart said. It can't be contracted by humans, although NOAA recommends against touching any dolphins found washed ashore.

This isn't the first time a morbillivirus has hit Florida's dolphin population. From June 1988 to May 1989, 742 dolphins — fewer than have died so far this year — died off the Atlantic coast from morbillivirus. Scientists estimated that during that epidemic, more than half the in-shore population of dolphins had been wiped out.

The 1980s dolphin die-off, the first to be attributed to morbillivirus, began the same way as this one. The first dead dolphins showed up around New York in the summer and then the epidemic made its way down the coast to Florida, persisting here until it ended at last the following spring.

Based on that pattern, Mase said, a lot more Florida dolphins are likely to die before the illness dissipates sometime next May.

"As the migratory population moves southward, you can expect the numbers in Florida to increase," Mase said.

There is no antiviral vaccine to give the dolphins to stop the die-off, just as there appears to be no way to halt the die-offs in Indian River Lagoon or along the Panhandle beaches. Scientists can only monitor what's happening and hope to discern the cause.

To Bossart, what's happening suggests that dolphins may be getting sick because the ocean around them is sick as well. Even before they began dying in droves, the dolphins in the Indian River Lagoon had high levels of mercury in their systems and quite a few were suffering from a fungal skin infection called lobomycosis.

"We've used the ocean as our toilet," he said, "and now it's starting to catch up with us."

Times researcher Natalie Watson contributed to this report, which contains information from Florida Today. Craig Pittman can be reached at craig@tampabay.com or via Twitter at @craigtimes.