Dolphins are dying in great numbers in the northern Gulf of Mexico.
Since February 2010, 1,308 dead or dying marine mammals — mostly bottlenose dolphins, including juveniles or aborted fetuses — have washed ashore on beaches and wetlands from Texas to Florida, or have been discovered floating in the Gulf’s murky waters.
In some months, the numbers of stranded dolphins in Louisiana, Mississippi and Alabama have exceeded past averages by three and a half to four times. In Louisiana, the 2010 and 2011 figures were the highest ever recorded.
A scientific explanation has so far proved elusive. “The Gulf is not a controlled laboratory where you can have a perfectly pathogen-free animal and expose it to one agent and measure the effect,” said Dr. Stephanie Venn-Watson, director of the translational medicine and research program at the National Marine Mammal Foundation.
Many critics suspect the BP Deepwater Horizon disaster in April 2010, and scientific evidence is building. According to an analysis that Dr. Venn-Watson and her colleagues published Feb. 11 in PLOS One, bottlenose dolphin deaths from January 2010 to June 2013 fell into four distinct clusters, indicating that there are likely multiple factors at play.
One group of deaths occurred before the oil spill, in and around Lake Pontchartrain. The researchers think unusually cold weather combined with freshwater intrusion most likely caused those deaths.
The other three clusters of deaths occurred after the spill, however, and largely in places affected by heavy, ongoing oil contamination. The researchers found no evidence that morbillivirus, a measleslike pathogen implicated in other die-offs, or toxins from harmful algal blooms played a role.
Additionally, some injuries, including lung and adrenal lesions, observed in 2011 in live dolphins examined in Louisiana’s Barataria Bay were consistent with exposure to petroleum products.
Dr. Venn-Watson and her colleagues plan to examine tissue samples collected from stranded dolphins and continue to monitor live ones. “The investigation is certainly still underway,” she said. “It’s not as straightforward as finding a bird or turtle covered in oil.”
–From New York Times