2019-2023 Eastern North Pacific Gray Whale UME (CLOSED)

The Unusual Mortality Event (UME) involving stranded eastern North Pacific gray whales along the western coast of North America has ended. It occurred from December 17, 2018 through November 9, 2023, with peak strandings occurring between December 17, 2018, and December 31, 2020. NOAA Fisheries and partners investigated the event.

The UME involved 690 gray whale strandings, including 347 in the United States, 316 in Mexico, and 27 in Canada. Strandings occurred from Alaska to Mexico along the west coast of North America, including in the whale’s wintering, migratory, and feeding areas. The Investigative Team concluded that the preliminary cause of the UME was localized ecosystem changes in the whale's Subarctic and Arctic feeding areas that led to changes in food, malnutrition, decreased birth rates, and increased mortality all documented during the UME.

Findings in Whales

Necropsy findings from a subset of dead gray whales found malnutrition as a common cause of death and did not identify underlying disease. Killer whale predation, entanglement, and vessel strike also caused deaths, and biotoxins were found in some carcasses as in non-UME years. The nutritional condition of live gray whales in Mexico was lower leading into and during the UME compared to the years before the UME.

Gray Whale Abundance and Distribution

Abundance estimates of the eastern North Pacific gray whale population show that it declined during the UME, from 20,500 whales in 2019 to 14,526 whales in 2023. Total calf production also declined from around 950 calves in 2018 to an estimated 217 calves in 2022. In 2023, calf production increased slightly to 412.

There have been recent changes in gray whale distribution and feeding behaviors as well as changes in gray whale prey associated with ecosystem changes in sub-Arctic and Arctic feeding areas. Gray whale population modeling, which focused on localized feeding areas in northern Bering and Chukchi seas, linked the 1999–2000 UME and the 2019–2023 UME to changes in sea ice cover and in the amount of gray whale prey. These impacts to prey likely led to malnutrition, decreased birth rates, and the increased mortality documented in the elevated strandings observed during the UME.

Gray Whale Strandings 2019–2023

Interactive Map

2019-2023 Gray Whale Unusual Mortality Event Dead Animal Locations Mapping Application