The mysterious deaths of 30 large whales in the western Gulf of Alaska is being declared an "unusual mortality event" by the National Oceanic & Atmospheric Administration, the agency said Thursday.

Since May 2015, 11 fin whales, 14 humpback whales, one gray whale, and four unidentified marine mammals have been stranded around the islands of the western Gulf of Alaska and the southern shoreline of the Alaska Peninsula. To date, this brings the number of whale strandings for this region to almost three times the historical average, according to a statement from NOAA.

The “unusual mortality event” designation will allow NOAA to work in tandem with federal, state, and tribal partners to conduct an investigation and come up with a response plan. A UME is defined by the government agency as a casualty event that is significant to the population (whales, in this case), is unexpected, and demands urgent action. The current priority for the agency is to determine the causes of death for the 30 whales found beached along the Alaskan coast since May.

"NOAA Fisheries scientists and partners are very concerned about the large number of whales stranding in the western Gulf of Alaska in recent months," said Dr. Teri Rowles, NOAA Fisheries' marine mammal health and stranding response coordinator in a statement. "While we do not yet know the cause of these strandings, our investigations will give us important information on the health of whales and the ecosystems where they live. Members of the public can greatly assist the investigation by immediately reporting any sightings of dead whales or distressed live animals they discover."

Only one whale of the 30 reported has been sampled, and scientists have been unable to determine a cause of death.

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Since 1991, when the "UME" was adopted as part of the Marine Mammal Protection Act of 1972, 61 such cases have been declared, and 29 have been solved. Understanding and investigating marine mammal UMEs is important because they can serve as indicators of ocean health, and provide insight into larger environmental trends which have implications for human health and welfare, according to NOAA. The agency’s mission is to track and predict changes in the Earth's environment, “from the depths of the ocean to the surface of the sun”.

Members of the public are urged by NOAA to assist in the investigation by immediately contacting the Alaska Marine Mammal Stranding Network hotline at 877-9-AKR-PRD (877-925-7773) if they see a stranded or dead marine mammal.