Dear EarthTalk: Do scientists have any idea why so many whales are dying in the Gulf of Alaska lately? – Michelle DiCostanzo, New York, NY

Over the past four months, 33 large whales have been reported dead in the Western Gulf of Alaska, which encompasses the areas around Kodiak Island, Afognak Island, Chirikof Island, the Semidi Islands and the southern shoreline of the Alaska Peninsula. The significant die-off of whales has been declared an Unusual Mortality Event (UME) by the National Oceanic and Atmospheric Administration (NOAA), marking the first large whale UME ever in Alaska.

The majority of the deceased humpback, fin and gray whales have been found moderately to severely decomposed and scientists have only been able to obtain samples thus far from one fin whale. Alaskan citizens have been instructed to call the Alaska Marine Mammal Stranding Network hotline immediately if a stranded or dead whale is spotted to ensure the fastest response possible by trained experts.

“Large whale UMEs are the most difficult UMEs to deal with, principally because the animals are floating and rarely beached and we have a difficult time getting to the carcasses to actually examine them,” says Dr. Teri Rowles, Coordinator of the NOAA Fisheries Marine Mammal Health and Stranding Program. “The most critical thing for this UME, given it is large whales, is our ability to get to the animals, document them, and if possible perform sample collections either at sea or on the beach if they are stranded. It is critical that the public and mariners report large whale mortalities or animals that they see in distress as soon as possible so that the Network can either document, access or track the carcasses.”

Exposure to harmful algae blooms (HAB) is NOAA’s leading theory for the cause of the surge in whale deaths. While the organization has collected some disparate samples of phytoplankton in the Gulf of Alaska that they determined could possibly produce biotoxins, there is no conclusive data currently associating the whale deaths to HAB, and the fin whale sample tested negative for HAB biotoxins.

“Even though the one sample we tested was negative, it was not the most appropriate sample to collect and test for biotoxins. We can’t rule it out based on the results we have right now,” Rowles adds. “It’s my understanding that sea surface water and air temperatures in the Gulf of Alaska have been high, and that always concerns us because that means there’s probably a change in overall pathogen exposure-possibly HABs and other factors.”

Claims that the UME is linked to the Fukushima nuclear reactor meltdown or the Navy-led “Northern Edge” military training exercises conducted in the Gulf of Alaska this past June have been dismissed due to lack of evidence. Muscle tissue from the fin whale sampled was sent to the University of Alaska Fairbanks for cesium analysis, and the preliminary results did not suggest any unusual exposure to manmade radiation. As the investigation continues, NOAA will be publishing updated information pertaining to the UME on their website as it becomes available; however, the investigation could take months or even years to complete.

“It takes a fair amount of time to pull data together even if the event is over, and a lot of deliberation and analyses have to happen in order to determine what’s going on,” Rowles added. “It could be quite a period of time before we actually have an answer, if indeed we end up with a definitive answer for this UME.”

CONTACT: NOAA Fisheries,

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