BILOXI, Mississippi (Reuters/Leigh Coleman) - The death toll of dolphins found washed ashore along the U.S. Gulf Coast since last month climbed to nearly 60 on Thursday, as puzzled scientists clamored to determine what was killing the marine mammals.
The National Oceanic and Atmospheric Administration declared the alarming cluster of recent dolphin deaths "an unusual mortality event," agency spokeswoman Blair Mase told Reuters.
"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, all were being examined as possible casualties of petrochemicals that fouled the Gulf of Mexico after a BP drilling platform exploded in April 2010, rupturing a wellhead on the sea floor, officials said.
Eleven workers were killed in the blast, and an estimated 5 million barrels (205.8 million gallons) of crude 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.
"We are on high alert here," said Moby Solangi, director of the private Institute of Marine Mammal Studies in Gulfport, Mississippi. "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."
At least 29 of the specimens recovered in recent weeks have been positively identified as bottlenose dolphins.
Solangi said that scientists from his organization have performed full necropsies, the animal equivalent of autopsies, on about a third of the roughly two dozen dead calves.
"The majority of the calves were too decomposed to conduct a full necropsy, but tissue samples were collected for analysis," he said.
The latest wave follows an earlier tally of 89 dead dolphins -- virtually all of them adults -- reported to have washed ashore in 2010 after the Gulf oil spill.
Results from an examination of those remains, conducted as part of the government's oil spill damage assessment, have not been released, though scientists concluded those dolphins "died from something environmental during the last year," Mase said.
"The number of baby dolphins washing ashore now is new and something we are very concerned about," she added.
Copyright 2011 Thomson Reuters. Click for Restrictions.