July 20, 2012
Dolphin Deaths In The Gulf Of Mexico Caused By Numerous Factors
redOrbit Staff & Wire Reports - Your Universe Online
The largest oil spill along the northern Gulf of Mexico to date, along with other environmental factors, led to the historically high number of dolphin deaths in the Gulf, concludes a two-year scientific study released on July 19, 2012.Since 2010, scientists have been trying to figure out why there were a high number of dolphin deaths, part of what is called an "unusual mortality event."
The most disturbing thing to scientists was the exceptionally high number of young dolphins that made up almost half of the 186 dolphins that washed ashore from Louisiana to western Florida from January to April 2010. The number of "perinatal" (near birth) dolphins stranded during this four-month period was six times higher than the average number of perinatal strandings in the region since 2003 and nearly double the historical average.
"The oil spill and cold winter of 2010 had already put significant stress on their food resources, resulting in poor body condition and depressed immune response. 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," Worthy added.
The cold winter of 2010 was followed by the historic BP Deepwater Horizon disaster in April 2011, which dumped millions of gallons of oil into the Gulf of Mexico, very likely disturbing the food chain. This was in the middle of the dolphins' breeding season. A sudden entry of high volumes of cold freshwater from Mobile Bay in 2011 imposed additional stress on the ecosystem and specifically on dolphins that were already in poor body condition.
"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 and resulted in distinct patterns in when and where they washed ashore," said Ruth Carmichael, a senior marine scientist at the Dauphin Island Sea Lab, an assistant professor of Marine Sciences at the University of South Alabama and the lead author of the study.
The majority of perinatal strandings were centered on the Mississippi-Alabama coast, adjacent to Mobile Bay, the 4th largest freshwater drainage in the U.S. The onshore movement of surface currents during the same period resulted in animals washing ashore along the stretch of coastline where freshwater discharge was most intense.
A team of biologists from several Gulf of Mexico institutions and the University of Central Florida in Orlando published their findings in the journal PLoS ONE.