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NOAA Actively Investigates Dolphin Deaths

An increase in stranded dolphins in the northern Gulf of Mexico has leading marine mammal researchers and citizens concerned. Using a suite of scientific analysis, NOAA and its state partners are currently working to try and solve the mystery of these dolphin deaths and strandings which began in February 2010 and is still ongoing.

“NOAA Fisheries is actively working with the Marine Mammal Stranding Network and the Gulf states to respond to and investigate these strandings,” said Blair Mase, NOAA Fisheries southeast marine mammal stranding coordinator. “Our scientists haven’t ruled out any potential factors and are performing rigorous tests to help determine potential causes or contributing factors.”

Dolphins may strand for many reasons—both natural and human influenced—and individual dolphin strandings are relatively common in coastal areas. However, scientists refer to unexpected and significant die-offs of marine mammals as “Unusual Mortality Events,” the designation of which triggers a multilevel response and investigation. Potential causes of large scale marine mammal die off events include disease, prey, unusual climate, and exposure to algal or chemical toxins.

NOAA declared an “Unusual Mortality Event” for the northern Gulf of Mexico beginning in February 2010, and it has continued into early 2011.

From February 2010 through April 3, 2011, 406 whales and dolphins — nearly all bottlenose dolphins — stranded on the shores of Louisiana, Mississippi, Alabama and the panhandle of Florida. Among these strandings were 86 premature or “neonatal” dolphins. Premature dolphin strandings, though not uncommon during the spring each year, were particularly high in Mississippi and Alabama in February and March of 2011.

Since 1991, the Gulf of Mexico has experienced 11 unusual mortality events involving bottlenose dolphins. In the past, caus es of U MEs in the Gulf have been attributed to biotoxins (53%), infectious diseases (7%), or unknown causes (40%).

Scientists are currently testing dolphin tissue samples for possible causes of death such as viruses, biotoxins, and any potential link to the Deepwater Horizon/BP oil spill. At this time a cause for these strandings has not yet been determined and a full analysis of the tests is expected to take many months or longer to complete.

Sea Turtle Strandings Also on the Rise

Dolphins are not the only species experiencing strange stranding events in the Gulf of Mexico. Just this month, NOAA’s Office of Protected Resources announced that there was a notable increase in sea turtle strandings as well.

While turtle strandings in this region typically increase in the spring, the recent increase is cause for concern. NOAA, as part of the Sea Turtle Stranding and Salvage Network (STSSN), is currently monitoring and investigating this increase.

NOAA scientists have conducted necropsies, which are animal autopsies, on 26 of the turtles (mostly Kemp's ridley turtles) recovered in March. Of the 26 turtles, 7 had major traumatic injuries. Six had injuries consistent with watercraft strikes and one was injured internally by a hook. The remaining 19 turtles had no external traumatic injuries, were in good nutritional condition and had sediment in their lungs found when turtles drown. Based on this, the two considerations are forced submergence typically in fishing gear or acute toxicosis from a biotoxin.

Testing is underway for biotoxins in the Gulf and information on fisheries operating in the area is also being assembled. The full results of these tests will take time to analyze.