Frequent Questions: West Coast Gray Whale Unusual Mortality Event

Why was the Unusual Mortality Event closed?

The increased stranding rate that triggered the Unusual Mortality Event declaration is no longer occurring. Stranding rates have returned back to normal and expected levels, and the prevalence of thin live or thin dead whales has also decreased.

How widespread was this Unusual Mortality Event?

Strandings of eastern North Pacific gray whales occurred in the United States, Canada and Mexico along the west coast of North America. They occurred in wintering, migratory, and feeding areas.

When did this Unusual Mortality Event occur? How many gray whales were included?

The Unusual Mortality Event occurred between December 17, 2018 to November 9, 2023, with peak strandings occurring between December 17, 2018, and December 31, 2020. There were a total of 690 gray whale strandings (347 in the United States, 316 in Mexico, and 27 in Canada).

What do scientists believe is the most likely cause of this Unusual Mortality Event?

The Investigative Team concluded localized ecosystem changes, including both access to and quality of prey, in the northern Bering and Chukchi seas caused the UME. These changes contributed to the poor nutritional condition observed in live whales in the wintering areas of Mexico and dead stranded gray whales in all three countries. This malnutrition led to increased mortality during the whales’ annual northward migration (from Mexico to Alaska) and decreased production of calves. This resulted in an overall decline in population abundance.

Did climate change contribute to the Unusual Mortality Event?

While recent environmental changes in the Arctic contributed to the poor nutritional condition of some whales during the migration, it is not clear whether long-term climate change played a role. Gray whales have experienced similar declines before but their numbers fully recovered. We will continue monitoring the population to track such changes.

What is next now that the Unusual Mortality Event has been closed?

Marine mammal stranding networks from the United States, Canada, and Mexico will continue to respond to stranded whales and fully sample the animals when feasible.

NOAA Fisheries Southwest Fisheries Science Center conducted a 2023–2024 survey to assess gray whale abundance. The SWFSC will carry out a 2024 survey to evaluate calf production.

What is the status of the eastern North Pacific gray whale population?

Gray whales were hunted nearly to extinction by commercial whaling. However, due to international conservation measures and the Marine Mammal Protection Act in the United States, the eastern North Pacific population has since recovered.

The whales continue to face human-caused threats despite their population recovery. These threats include entanglement in fishing gear, collisions with vessels, and disturbance from underwater ocean noise. A western North Pacific population of gray whales, which summers off the Russian coast in the Okhotsk Sea, remains endangered.

Do all gray whales migrate to the Arctic?

No. Most eastern North Pacific gray whales migrate between the feeding grounds off Alaska and the wintering grounds in Mexico. A few hundred individuals, known as the “Pacific Coast Feeding Group,” do not travel to the Arctic. Instead, they feed along the Pacific coast between southeast Alaska and northern California. These whales typically overwinter in Mexican waters with other eastern North Pacific gray whales.  

What is the size of the eastern North Pacific gray whale population along the West Coast?

View the current estimate for the number of eastern North Pacific gray whales. The eastern North Pacific gray whale population is still not considered threatened or endangered under the Endangered Species Act but remains protected by the Marine Mammal Protection Act.

How many gray whale UMEs have previously occurred along the west coast?

One previous UME involving Eastern North Pacific gray whales occurred between 1999-2000. This event occurred throughout the species’ range in Mexico, the United States, and Canada, with more than 650 animals stranded along the west coast of North America including 222 in the United States (Gulland et al. 2005). Some of the stranded whales were emaciated and calf production in 1999 and 2000 was less than one third of that in 1996–98. Oceanographic factors that limited food availability for gray whales were identified as likely causes of the UME, with resulting declines in survival rates of adults during this period.

Where do gray whales primarily feed?

Gray whales feed primarily in the Arctic in summer, consuming sea-bottom amphipods and other organisms living in and above the sediment and in the water column. They feed extensively during the summer and fall feeding season. They seek to consume enough food to survive the following 6 months, as they generally fast during their southbound migration and wintering season in Mexico. However some feeding on prey, including copepods, euphausiids, small fish and herring, may occur during the migration period. Gray whales face the greatest nutritional stress during the northbound migration, when they may be reaching the limits of their fat stores. If the whales do not consume enough food during the feeding season, they may not have enough nutritional stores to fuel their roundtrip migration back to the Arctic (roughly 10,000 miles). We monitor this situation as part of annual surveys conducted along the California Coast.

How many gray whale Unusual Mortality Events have previously occurred along the West Coast?

One previous Unusual Mortality Event involving eastern North Pacific gray whales occurred between 1999–2000. This event occurred throughout the species’ range in Mexico, the United States, and Canada. More than 650 animals stranded along the U.S. West Coast including 222 in the United States. Some of the stranded whales were emaciated and calf production in 1999 and 2000 was less than one third of that in 1996–1998. The overall gray whale population is estimated to have declined from about 21,000 in 1997–1998 to 16,000 in 2000–2001. Oceanographic factors that limited food availability for gray whales were identified as likely causes of the UME, with resulting declines in survival rates of adults during this period.

What happened after the previous eastern North Pacific Gray Whale Unusual Mortality Event (1999-2000)? Did the population recover?

In the following few years, gray whale strandings decreased to pre-1999 levels, calf production increased to more typical rates. The population rebounded to about 27,000 animals in 2015–2016 before the most recent UME). The gray whale population has demonstrated its resilience in recovering from endangered status (delisted in 1994) and again following the decline in abundance related to the 1999–2000 UME.

Where can I find additional information on gray whales and other Unusual Mortality Events?

View more information on gray whales and other Unusual Mortality Events.

What should people do if they encounter a live stranded whale or dead whale floating in the water or stranded on the beach?

Do not touch the whale or allow pets to approach the whale. Observe the animal from a safe and legal distance of at least 100 yards (safe for you and the animal). Please immediately contact your local or regional stranding network organization if you see a sick, injured, or dead whale at sea or stranded on a beach:

• In California, Oregon or Washington: Call the West Coast Marine Mammal Stranding Network: (866) 767- 6114
• In Alaska: Call the Alaska Marine Mammal Stranding Network: (877) 925-7773
• In Canada: Call the British Columbia Marine Mammal Response Network (800) 465-4336
• At sea: Contact the U.S. or the Canadian Coast Guard on channel 16 or the network phone line in the United States

What should people do if they witness harassment of a whale in the water or on the beach?

To report violations please contact NOAA’s Office of Law Enforcement at (800) 853-1964.

What is the UME Contingency Fund?

The Marine Mammal Unusual Mortality Event Fund is used by the Secretary of Commerce, in consultation with the Secretary of the Interior:

• To compensate persons for special costs incurred in acting in accordance with the contingency plan issued under section 1421c(b) of this title or under the direction of an Onsite Coordinator for an unusual mortality event

• For reimbursing any stranding network participant for costs incurred in preparing and transporting tissues collected with respect to an unusual mortality event for the Tissue Bank

• For care and maintenance of marine mammals seized under section 1374(c)(2)(D) of this title”

The National Contingency Plan for Response to Unusual Marine Mammal Mortality Events outlines the types of expenses that are reimbursable under the fund and the process for requesting reimbursement. 

Learn more about the UME Contingency Fund.

How can deposits be made into the UME Contingency Fund?

The following can be deposited into the fund:

• Amounts appropriated to the fund
• Other amounts appropriated to the Secretary for use with respect to UMEs
• Amounts received by the United States in the form of gifts, devises, and bequests under subsection (d) of section 405(d) of the Marine Mammal Protection Act

You can use Pay.gov to donate to the UME Contingency Fund for this or other UMEs and help cover costs incurred by the Marine Mammal Stranding Network.