Snowmelt water and the 2010 BP oil spill, both the natural factor and human catastrophe, caused the death of 86 baby dolphins who were either aborted or died shortly after birth in early 2011 in the Gulf of Mexico, a new study suggests.
"Unfortunately, it was a 'perfect storm' that led to the dolphin deaths," Graham Worthy, study researcher and a biologist at the University of Central Florida, said in a statement. "The oil spill and cold water of 2010 had already put significant stress on their food resources. ... It appears the high volumes of cold freshwater coming from snowmelt water that pushed through Mobile Bay and Mississippi Sound in 2011 was the final blow."
According to Ruth H. Carmichael, senior marine scientist at Alabama's Dauphin Island Sea Lab, the bottlenose dolphins, who were already suffering from the issue of premature birth for the 2010 oil spill event, succumbed to death due to the extremely harsh winter of 2010.
"When we put the pieces together, it appears that the dolphins were likely weakened by depleted food resources, bacteria or other factors as a result of the 2010 cold winter or oil spill, which made them susceptible to assault by the high volumes of cold freshwater coming from land in 2011," Carmichael said in a statement. She further added that "These freight trains of cold fresh water may have assaulted them, essentially kicking them when they were already down," she said.
While dolphins are naturally able to tolerate fluctuating temperatures, a National Oceanic and Atmospheric Administration (NOAA) survey of dolphins in Barataria Bay during the summer of 2011 indicated that the animals were already sickly underweight and anemic, had low blood sugar, liver and lung disease along with low levels of hormones to respond to stress, metabolism and immune function. Therefore, they could not battle against the rapid entry of large volumes of cold melt water in the upper reaches of the Mobile Bay watershed.
"From studies of other mammals we know that adrenal insufficiency can lead to some fairly severe health problems; it can cause low blood sugar, weight loss, low blood pressure and eventually even lead to kidney and heart failure and death," Lori Schwacke of National Oceanic and Atmospheric Administration said during a news briefing. "So we're concerned that many of the Barataria dolphins are in such poor health that they're likely not to survive."
NOAA scientists, along with a team of marine mammal health experts, are investigating the causes of high dolphin mortality in the region.
The study was published on July 18 in the PLoS ONE journal.