A new report published in the journal PLoS One, suggests that a 'perfect storm' of events contributed to the deaths of dolphins in the Gulf of Mexico.
In a recent interview with NOAA Fisheries Service, the National Oceanic and Atmospheric Administration revealed how Gulf region dolphins are already facing multiple threats from entanglement in fishing lines, harassment, strandings and illegal feedings.
Preliminary data from NOAA Fisheries says that as of July 15, 2012, there have been 754 cetacean strandings in the Northern Gulf of Mexico. The deaths, described as "unprecedented" by the NOAA, prompted an ongoing unusual mortality event (UME), initiated long before the Deepwater Horizon Oil Spill (DWHOS).
The UME has so far not been linked to DWHOS by the Fisheries Service, but a new report by a team of scientists from several Southern universities and research institutes, including the Dauphin Island Sea Lab and the University of Central Florida, is suggesting that unusually cold water in the Gulf of Mexico and damage to the food web from DWHOS, may have caused the premature deaths of hundreds of dolphins in the region.
The report called "Were Multiple Stressors a ‘Perfect Storm’ for Northern Gulf of Mexico Bottlenose Dolphins (Tursiops truncatus) in 2011?," said that "Preceding the stranding event, large volumes of cold freshwater entered the nGOM [northern Gulf of Mexico] due to unusually large snowmelt on the adjacent watershed, providing a third potential stressor."
The other stressors scientists said, were "two well documented environmental perturbations; sustained cold weather in 2010 and the Deepwater Horizon oil spill."
During a 4-month period the report explained, beginning January 2011, "186 bottlenose dolphins, including 46% perinatal calves (nearly double the percentage for the same time period from 2003–2010) washed ashore from Louisiana to western Florida.".
The University of Central Florida's Graham A.J. Worthy, a biologist who contributed to the report, told the New York Times:
"What we do know was that there was a cold winter in 2010 which might have affected dolphin food resources, and the BP oil spill occurred in 2010, and there is increasing evidence of spill materials entering coastal ecosystems and negatively impacting the food web," he said.
In 2011, NOAA marine mammal biologists along with local, state, federal and other research partners initiated the Bataria Bay dolphin study as part of the Natural Resource Damage Assessment (NRDA) for studying the effects of the Deepwater Horizon spill.
After physically examining 32 live bottlenose dolphins, it was determined that many of them were underweight, anemic, had low blood sugar levels and symptoms of liver or lung disease. Almost half of them had reduced immune function due to lowered levels of hormones that control stress.
Under normal conditions said report researchers, healthy dolphins would have been able to withstand this cold flow, but "due to depleted food resources, bacterial infection, or other factors," the report added, "it is plausible that the spring freshet contributed to the timing and location of the unique stranding event in early 2011."
The study, Worthy told the Times, was not conclusively linking the dolphin deaths to the oil spill but was rather seeking contributing elements. "Everything ultimately seems to be linked back to poor body condition" he said. But it seems what caused the poor body condition in the first place, is still open to much debate.