My guess is the millions of barrels of toxic dispersant they used to disappear the oil.

Dead baby bottlenose dolphins are continuing to wash up in record numbers on the shores of the Gulf of Mexico, and scientists do not know why.

Since February 2010 to April 2011, 406 dolphins were found either stranded or reported dead offshore.

The occurrence has prompted the National Oceanic and Atmospheric Administration to designate these deaths as an “unusual mortality event” or UME. The agency defines a UME as a stranding incident that is unexpected or involves a significant loss of any marine mammal population.

“This is quite a complex event and requires a lot of analysis,” said Blair Mase, the agency’s marine mammal investigations coordinator.

Mase said NOAA is working closely with a variety of agencies to try to figure out not only why the bottlenose dolphins are turning up in such large quantities but also why the mammals are so young.

“These were mostly very young dolphins, either pre-term, neonatal or very young and less than 115 centimeters,” she said.

Marine mammals are particularly susceptible to harmful algal blooms, infectious diseases, temperature and environmental changes, and human impact.

“The Gulf of Mexico is no stranger to unusual mortality events,” Mase said.

Sensitivity surrounding marine life in the area is particularly high after the BP oil disaster that sent millions of barrels of crude into the Gulf of Mexico nearly a year ago.

via Scientists unsure why dolphins washing up dead – CNN.com.