Usually, a few dead dolphins wash ashore along gulf beaches in the first few months of the year. Some are killed by Red Tide or other toxic algae blooms, some by diseases, some by cold.
But this year something different is happening. Since Jan. 1, there have been 48 bottlenose dolphins washed up on the beaches of Louisiana, Mississippi, Alabama and Florida's Panhandle.
Most of them — 29, including two of the three found in Florida — were newborn, miscarried or stillborn calves. There were reports of five more washing ashore Thursday, but scientists had not yet verified them or added them to the official count.
The suspicion is that somehow the oil or chemical dispersants from summer's Deepwater Horizon disaster killed them. Activists from the National Wildlife Federation and other groups blogging about the deaths and posting items on Twitter have linked the spike in deaths to the oil spill. ABC and CNN have jumped on the story.
However, the culprit could turn out to be something else, scientists say.
"We shouldn't jump to conclusions," cautioned Randy Wells, a Mote Marine Laboratory scientist who has spent nearly 40 years studying dolphins.
Tests of the carcasses to pinpoint the cause will likely take months, said Blair Mase of the National Oceanic and Atmospheric Administration, which is overseeing the investigation.
Still, everyone acknowledges that the wave of dead dolphins signals something out of the ordinary.
"What's unusual is that there are so many, and so many of them are so young," said Mase, who is in charge of the NOAA's marine mammal stranding network for the southeastern states.
The gestation period for dolphins is between 11 and 12 months. That means dolphins dying now were likely conceived before the April 20 rig explosion off the Louisiana coast.
They were in the early stages of development as about 4.9 million barrels of oil gushed into the gulf, and BP was spraying 771,000 gallons of chemical dispersant on the flow.
Although federal officials and BP have scaled back the cleanup, Louisiana officials say they're still seeing oil washing ashore.
A recent study of the area around the spill by University of Georgia scientist Samantha Joye found dead corals, crabs and sea stars scattered on the sea floor, along with strings of bacterial slime that created what she called an "invertebrate graveyard."
Still, Mase said that many things can lead to animal deaths. "Since 1990, we have had 13 unusual mortality events in the Gulf of Mexico. … So the oil spill is one of the things we're looking into."
There are arguments to be made, though, against some of those other possible causes.
If the dolphins were killed by the winter cold, other species would likely be affected, too, said Moby Solangi, director of the Institute for Marine Mammal Studies, which has collected a majority of the dolphin carcasses, all of them from a 130-mile stretch of beach in Alabama and Mississippi.
So far, all Solangi's staff has been finding have been very young dolphins.
"The usual thing with strandings is that we see a mix of old and young dolphins," Solangi said. "But these all appear to be stillborn or they survived just a day or two before dying."
A Red Tide bloom hasn't been reported in the northern gulf, so that seems unlikely as a cause. That still leaves bacterial or viral infections among possibilities.
Steve Shippe of the Emerald Coast Wildlife Refuge in Fort Walton Beach led the group that picked up the two young dolphins found in the Florida Panhandle — one Jan. 5 in Gulf Breeze, one Jan. 25 on Pensacola Beach.
Although Shippe is studying the oil spill's impact on dolphins, he's reluctant to blame those two on BP. "This is kind of a historical average for our part of the gulf coast," he said.
But the large numbers washing ashore on the Alabama and Mississippi beaches could be a sign of something strange at work, he said.
Shippe, Mase and Solangi all pointed out one thing: The dolphin birthing season hasn't hit its peak yet. That begins at the end of February/beginning of March — so the tide of dead dolphins may not be over.
Craig Pittman can be reached at firstname.lastname@example.org.