Scientists are looking for a possible link between a surge in deaths among baby dolphins in the Gulf of Mexico and the BP oil spill.
So far this year, 29 newborn dolphins have washed up on the northern shores of the Gulf of Mexico, far higher than seen in typical years.
US government scientists said it was too early to conclude that there is a link with the explosion at BP's well last April, which dumped 4.9m barrels of oil into the Gulf, but that it was a definite possibility.
There are suggestions that the timing of the spill may have been a contributory factor. As most of the dolphins were conceived before last April and their gestation period is 11 or 12 months, some experts have speculated the spill compromised the pregnancies and the development of the calves. A number of press reports have also said that one or two of the dolphin corpses appeared to be covered in oil.
However, scientists cautioned that the deaths – entirely among one species – could be caused by disease, a decrease in food supply, or a sudden dip in water temperature. Dolphins weakened by those factors could also be more vulnerable to other dangers such as toxic algae blooms known as "red tides", or industrial pollution. The waters of the Gulf have long been degraded because of pollution.
Although scientists typically only see one or two such deaths a year, this is not the first case of mass dolphin deaths in the Gulf.
"There was already an unusual mortality event in that region even before the Deepwater Horizon oil spill started," said conservation scientist Randall Wells, who heads a team at the National Oceanic and Atmospheric Administration investigating unusual mortality events.
The definitive conclusion on what caused the deaths will have to wait until the results of necropsies on six dead calves at the Institute for Marine Mammal Studies in Mississippi, which will include tests for toxins related to the oil spill.
"Just because there was a horrible, horrible, horrible oil spill last year doesn't mean that is what caused the deaths of these babies right now – though it could very well," Wells said.