The National Oceanic and Atmospheric Administration declared the alarming cluster of recent dolphin deaths "an unusual mortality event," agency spokeswoman Blair Mase.
"Because of this declaration, many resources are expected to be allocated to investigating this phenomenon," she said.
Although none of the carcasses bore outward signs of oil contamination, the alarmingly high number of dead young dolphins are being looked at as possible casualties of oil that fouled the Gulf of Mexico after a BP drilling platform exploded in April 2010, killing 11 workers and rupturing a wellhead on the sea floor.
An estimated 5 million barrels (205.8 million gallons) of oil spilled into the Gulf over more than three months.
As of Thursday, the remains of 59 dolphins, roughly half of them newly born or stillborn calves, have been discovered since January 15, on islands, in marshes and on beaches along 200 miles of coastline from Louisiana east across Mississippi to Gulf Shores, Alabama, officials said.
That tally is about 12 times the number normally found washed up dead along those states during this time of the year, which is calving season for some 2,000 to 5,000 dolphins in the region.
"When the world sees something like baby dolphins washing up on shore, it pulls at the heartstrings, and we all want to know why," said Blair Mase, marine mammal strandings coordinator for the Southeast region of National Oceanic and Atmospheric Administration.
That tally is more than 10 times the number normally found washed up along those states during this time of the year, which is calving season for some 2,000 to 5,000 dolphins in the region, said Moby Solangi, director of the Institute of Marine Mammal Studies in Gulfport. At least 29 of the specimens recovered in recent weeks have been positively identified as bottlenose dolphins.
"We are on high alert here," said Solangi. "When we see something strange like this happen to a large group of dolphins, which are at the top of the food chain, it tells us the rest of the food chain is affected."
"It's an anomaly," he told Reuters by telephone, explaining that the gestation period for dolphins runs 11 or 12 months, meaning that calves born now would have been conceived at least two months before the oil spill began.
Most of the carcasses, measuring just over 3 feet in length, were found during the past week, the bulk of them washing up in Mississippi and Alabama.
The remains of about 10 adult dolphins, none of them pregnant females, have also been found so far this year.
BP cleanup crews found some of the carcasses. Others were discovered by park rangers, police and passersby.
"What makes this so odd is that the dolphins were spread out over such a large area," Solangi said.
Dolphins encountering oil on the surface of the water would face serious health consequences, Solangi said.
"We take short breaths. These animals take a huge breath at one time and hold it. And when they take it, the fumes stay in the lungs for a long period of time and they cause two types of damage, one of which is immediate to the tissue itself. Second, the hydrocarbons enter the bloodstream," he said.
None of the carcasses bore any obvious outward signs of oil contamination. But Solangi said necropsies, the equivalent of human autopsies, were being performed and tissue samples taken to determine if toxic chemicals from the oil spill may have been a factor in the deaths.
Documented mortality in the adult dolphin population off the Gulf Coast roughly tripled from normal numbers last year, climbing from about 30 typically reported in a given year to 89 in 2010, Solangi said.
Reuters: ,"Baby dolphin deaths rise along Gulf Coast ", by Steve, Gorman, accessed February 23, 2011
Reuters, "Gulf Coast dolphin death toll rises to nearly 60", accessed February 25, 2011