Events have taken a deadly turn for whales in the Gulf of Alaska in the past few months. Since the end of May, 30 large whales have been found dead in the area, which is nearly triple the historical average for the region. 

The National Oceanic and Atmospheric Administration (NOAA) has labeled the recent wave of deaths as an “unusual mortality event” and will start immediately studying the remains and the local ecosystem to try to track down a cause.

NOAA defines an unusual mortality event as one that is “unexpected, involves a significant die-off of a marine mammal population, and demands immediate response.” It could take scientists months or even years to explain the disturbing phenomenon. 

One theory that’s been all but ruled out is radiation exposure. The Fukishima nuclear disaster of 2011 is often blamed for environmental issues on the other side of the Pacific, but NOAA has said that the tissue samples they're testing show no signs of radiation.

Of the 11 fin whales, 14 humpbacks, one gray whale, and four unidentified species that have turned up dead in the region this season, scientists have only been able to collect tissue samples from one. Most of the carcasses were either decomposed beyond use or unable to be retrieved, and the one specimen the researchers did sample presented no clear cause of death. Locals can help with the ongoing investigation by reporting any washed-up whales they find. 

[h/t: NOAA Fisheries]