NEW ORLEANS — Scientists are trying to figure out what killed 53 bottlenose dolphins — many of them babies — so far this year in the Gulf of Mexico, as five more of their carcasses washed up Thursday in Louisiana, Mississippi and Alabama.

It's likely to be months before they get back lab work showing what caused the spontaneous abortions, premature births, deaths shortly after birth and adult deaths said Blair Mase, the National Oceanic and Atmospheric Administration's stranding coordinator for the Gulf Coast.

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"It's not like CSI where the very next day they have the results in. It doesn't work that way, unfortunately," she said.

Calves and fetuses made up at least 85 percent of the deaths in Alabama, 60 percent or more of those in Mississippi and Florida and 20 percent in Louisiana, according to NOAA figures.

The Mississippi and Alabama deaths are in areas where bottlenose dolphins go to calve, said Moby Solangi, director of the Institute for Marine Mammal Studies in Gulfport.

Solangi said he'd never seen anything like the calf deaths, or found word of anything like it in 30 years of records from his area — Alabama, Mississippi and east Louisiana.

However, Mase said 68 dolphins that washed up in east Texas in March 2007 also included an unusually large number of calves. The bodies were too decomposed to find the cause, she said.

Although scientists are investigating whether the deaths are related to last year's huge BP oil spill, they say toxins from oil or chemicals used to disperse it are considered a less likely cause than cold or disease. That's because only one species of dolphin — and no other kind of animal — is dying, and because the calf deaths appear concentrated in Mississippi and Alabama rather than Gulf-wide.

Patrick Semansky  /  AP

Technician Wendy Hatchett of the Institute for Marine Mammal Studies holds up a jar containing organ samples from dead dolphins found along the Gulf Coast in Gulfport, Miss., on Tuesday.

The dolphins found Thursday include three off Louisiana and one each off Mississippi and Alabama, NOAA spokeswoman Kim Amendola said. The bodies had not been retrieved, so ages and sizes were not known, she said.

Since Jan. 1, 19 dead dolphins have been found off Louisiana, 16 off Mississippi, 15 in Alabama and three in the Florida Panhandle. Mississippi and Alabama usually each see two to four dolphin strandings a month at this time of year, Mase said.

Solangi said only six of the 23 calves found by Wednesday in Mississippi and Alabama were in good enough condition for a necropsy, the animal version of an autopsy.

"We've collected tissues and sent them off to various laboratories for pathology and toxicology," he said. "All we can tell is some of them may have been premature, some of them were stillborn and others may have just survived for a day or two and died."

Dolphins usually calve in March and April, he said.

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Mase said dolphin stranding reports have been unusually high since January 2010. Last winter's deaths probably were caused by extreme cold, she said. "It was a very, very cold winter last year. We had a lot of turtle mortality, manatee mortality and dolphin mortality."

The Deepwater Horizon exploded into flames on April 20 and sank four days later. The spill response brought crews out to look for oiled wildlife and to clean the remote areas where most strandings occur, Mase said.

Because those areas are remote, there's no way to know the true numbers of dolphin strandings and deaths. "The number is not absolute — just a kind of barometer," Mase said.