Scientists with The University of Southern Mississippi Department of Marine Science, in collaboration with the Dauphin Island Sea Lab and the University of Central Florida, have taken part in a study to examine the increased mortality rates among dolphins along the Gulf Coast. Their findings has been featured in an -article in the journal PLoS-ONE, a peer-reviewed scientific journal published by the Public Library of Science.

The study examined 186 dolphins that washed ashore from Louisiana to western Florida during a four-month time period from January to April 2011. The dolphins are considered part of an “unusual mortality event” or UME by the National Oceanographic and Atmospheric Administration (NOAA). Although the strandings occurred shortly after the BP Deepwater Horizon disaster in 2010, scientists are working to determine the exact cause of death.

“We believe several factors, including bacterial infections and a loss of prey during the oil spill, contributed to the poor health of these marine animals,” said Dr. Monty Graham, chairman of The University of Southern Mississippi Department of Marine Science and a member of the consortium.

Additional contributing factors could include an unusually cold winter following the Deepwater Horizon oil spill. The sudden entry of high volumes of cold freshwater from Mobile Bay combined with onshore movement of surface currents during the same period imposed additional stress on the ecosystem. Although nearshore areas are regularly influenced by freshwater drainage, the watershed had experienced moderate to severe drought for several years. Therefore, researchers contend the dolphins were unable to swim away from the cold freshwater because of their compromised health.

“Surface currents, measured by coastal radars of USM’s Central Gulf of Mexico Ocean Observing System, indicated that onshore flow during this time would have helped to keep that cold water near the coast,” said University of Southern Mississippi associate professor of marine science Dr. Stephan Howden, who contributed to the research effort.

The stranded animals also included a higher number of young dolphins. The number of ‘perinatal’ (near birth) dolphins stranded during this four-month period made up nearly 46 percent of the deaths. This is six times higher than the average number of perinatal strandings in the region since 2003 and nearly double the historical percentage of all strandings. The majority of these were centered on the Mississippi-Alabama coast, adjacent to Mobile Bay, which is the fourth largest freshwater drainage in the U.S.

According to the study’s lead author, Dr. Ruth Carmichael from the Dauphin Island Sea Lab, targeted analyses of tissues from stranded dolphins are essential in assessing a cause of death. However, the research team hopes their findings highlight the importance of considering environmental data along with biological samples to interpret stranding patterns.

Learn more about The University of Southern Mississippi Department of Marine Science athttp://www.usm.edu/marine.

Image courtesy University of Southern Mississippi

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