An unusual mortality event, or UME for short, is defined under the Marine Mammal Protection Act as a stranding event that is unexpected, involves a significant die-off of any marine mammal population, and demands immediate response. There are seven criteria that make a mortality event "unusual." If the national Working Group on Marine Mammal Unusual Mortality Events, a group of marine mammal health experts, determines that an event meets one or more of the criteria, then it forwards a recommendation to NOAA’s Assistant Administrator for Fisheries to declare a UME.