Dolphins are washing up dead on the shores of the northern Gulf of Mexico, perplexing scientists as to the exact cause.
Since February 2010, over 1,300 dead or dying marine mammals, comprised mostly of bottlenose dolphins, have been found floating offshore of the Gulf or on its beaches and wetlands. Since few animals wash ashore or are found after death, the NOAA says that the carcasses represent only a fraction of the total marine mammals that have died.
The number of beached dolphins in Alabama, Mississippi, and Louisiana since 2010 have exceeded past averages by as much as four times. In 2010 and 2011, Lousiana reported more dolphin deaths than any point in its history. This unprecedented spike in stranded dolphins has led the NOAA to label it a Cetacean Unusual Mortality Event, and to launch a thorough ongoing investigation into its cause.
Some have pointed to the BP Deepwater Horizon disaster, which occured in April 2010, as the likely catalyst for the dolphin deaths. However, scientists have yet to pinpoint a definitive reason for most of the mortalities, saying multiple factors are likely at play.
Dolphin deaths that occured before the spill, in and around Lake Pontchartrain, were most likely due to cold weather and freshwater exposure. Several other deaths and injuries occured in areas that were largely affected by the BP oil spill, but researchers have not yet found a solid connection between the dead marine mammals and oil toxins. However, some injuries to dolphins found in 2011 were possibly due to their exposure to petroleum, and evidence linking the 2010 oil spill to the Unusual Mortality Event may be building.
Researchers say the investigation in still under way, and they will continue to analyze tissue samples from dead dolphins and monitor live specimens.