Mystery Dolphin Deaths

An unusually large number of young bottlenose dolphins have stranded along shores of the Gulf of Mexico in recent months, and last April’s catastrophic blowout of BP’s Deepwater Horizon oil rig is being eyed as the culprit. In just two months, 80 dead dolphins, including 42 calves, were found along the coasts of Alabama, Mississippi, Louisiana and Florida. The typical gestation period for a bottlenose dolphin is one year, with births usually taking place in March and April. One theory, therefore, for the large number of dead calves is that their mothers were exposed to oil during pregnancy, leading to aborted, stillborn, or premature calves.

Scientists are trying to determine causes of deaths, a task made difficult by the fact that oil hydrocarbons do not persist in the animals’ cell tissues. In April, however, it was reported that some of the dolphins who have washed ashore after the spill had oil on their bodies—some of which has been traced to the BP spill. Indirect effects from the spill also cannot be ruled out; the massive amounts of oil and dispersants released during the spill caused changes in ocean temperature and prey availability, and disrupted the habitat in ways that may never fully be measured.