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Dolphin Deaths Designated An ‘Unusual Mortality Event’

April 10, 2011

Scientists are baffled by the continuing numbers of dead baby bottlenose dolphins washing up on the shore of the Gulf of Mexico.

406 dolphins were found either stranded or dead between February 2010 and April 2011, prompting the National Oceanic and Atmospheric Administration (NOAA) to designate the deaths as an “unusual mortality event” (UME). The agency defines such events as a stranding incident that is unexpected or involves great losses of any marine mammal population.

Blair Mase, the agency’s marine mammal investigations coordinator, told CNN: “This is quite a complex event and requires a lot of analysis.”

Mase said NOAA is working with several agencies to determine not only why the dolphins are turning up dead in such large numbers but also why the mammals are so young. “These were mostly very young dolphins, either pre-term, neonatal or very young and less than 115 centimeters,” Mase said.

A number of factors could be at play including harmful algal blooms, infectious diseases, water temperatures, environmental changes, and human impacts. “The Gulf of Mexico is no stranger to unusual mortality events,” Mase noted.

Much sensitivity surrounding marine life has come about since last year’s BP oil disaster that spewed millions of barrels of crude oil in the Gulf waters.

As recently as two weeks ago, scientists documented a dead dolphin with oil on its remains, said Mase. Since the start of the oil spill on April 20, 2010, a total of 15 bottlenose dolphins have been found with either confirmed or suspected oil on their carcasses. Nine oiled dolphins have been found since the gushing oil well was capped.

But of those nine, one was found with oil that did not match that of samples from the Deepwater Horizon.

Mase said the dolphin deaths could be completely unrelated to the oil spill. “Even though they have oil on them, it may not be the cause of death,” she said. “We want to look at the gamut of all the possibilities.”

Scientists are also concerned over the number of sea turtles that are being stranded. Similar to the dolphin deaths , an abnormally high number of turtles have also been found floating close to shore or washed up along the Gulf coast shores.

“The vast majority of these are dead, with states in moderate to severe decomposition,” Barbara Schroeder, NOAA Fisheries national sea turtle coordinator, told CNN’s Vivian Kuo.

The majority of the turtles found have been Kemp’s Ridley sea turtles, but some have been loggerheads, which along with the Kemp’s are endangered.

“Since January 1st, we’ve had just under 100 strandings,” said Schroeder. “About 87 of those have been documented since the middle of March.”

Necropsies were performed on about a third of the turtles, Schroeder said. Seven of them showed indications that they had been in accidents with watercrafts, while another displayed injuries consistent with being caught on a hook.

The others appeared to have died by drowning near the bottom of the Gulf, either from forced submergence or an acute toxic event.

Tissue samples from both turtles and dolphins are being documented due to the civil and criminal litigation ongoing with BP, according to Dr. Teri Rowles, a coordinator with NOAA Fisheries Stranding Program.

“We are looking at what is the impact of the oil spill and the response activities to the oil spill event, and what impact they had on the Gulf of Mexico ecosystem,” said Rowles. “We did not say that the dolphins have died because of the oil, just that they have come back with oil on them.”

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