Discovery News says the 714 reported dolphin deaths are just the tip of a much larger iceberg:
NOAA declared the die-off an “Unusual Mortality Event” as per the Marine Mammal Protection Act of 1972.
Although the timing of die-off largely coincides with BP’s Deepwater Horizon oil spill and its aftermath, the deaths actually started increasing about two months before the April 20, 2010 explosion which started the months long oil spill.
Before the spill, 112 dolphins had already been reported stranded on the shore.
In the summer of 2011, NOAA tested 32 live dolphins in Barataria Bay, an area heavily impacted by the oil spill. The dolphins were underweight, anemic, had low blood sugar and/or some symptoms of liver and lung disease. Nearly half had abnormally low levels of hormones that help with stress response, metabolism and immune function.
The symptoms are consistent with those seen in animals exposed to oil.
It seems like there was a brucellosis outbreak shortly before the big spill, so the dolphin population got slammed by a one-two punch.