Unusual Mortality Event (UME) in Pacific Gray Whales

Saving Ocean Wildlife hosted a webinar on “Why are our Gray Whales Dying?” with Dr. Steven Swartz and Professor Jorge Urbán R. from the Laguna San Ignacio Ecosystem Science Program (LSIESP).  You can view the replay here. 

The Marine Mammal Protection Act (MMPA) was enacted in response to increasing concerns among scientists and the public that significant declines in some species of marine mammals were caused by human activities. The MMPA established a national policy “to prevent marine mammal species and population stocks from declining beyond the point where they ceased to be significant functioning elements of the ecosystems of which they are a part.” This was the first legislation to mandate an ecosystem-based approach to marine resource management rather than considering single issues, species, or ecosystems in isolation. An ecosystem-based approach provides insight into bigger environmental issues affecting marine mammal populations and overall ocean health, which in turn may affect human health.

Of significant concern to scientists are unusual mortality events (UME) in which a large number of individuals in a marine mammal population die from an (as yet) unknown cause. Under Title IV of the MMPA, an UME is defined as “a stranding that is unexpected; involves a significant die-off of any marine mammal population; and demands immediate response.” An UME is determined to be “unusual” if it meets one or more of seven defined criteria. All possible information is reviewed and, within 24 hours of the initial consultation, it is decided whether an event is considered an UME.

Causes for marine mammal UMEs include biomagnification of toxic chemicals through ocean ecosystems, plastic ingestion, biotoxins, infectious pathogens (bacterial and viral), human interactions, starvation, and other ecological factors. Some causes are undetermined.

Eastern North Pacific gray whales are experiencing an UME

Since December 2018 there has been a significant increase in Eastern North Pacific gray whale (Eschrichtius robustus) strandings and deaths along the west coast of North America from Alaska to Mexico. This event has been declared an Unusual Mortality Event (UME).

Map of gray whale UME along the west coast of North America through Jan 10, 2020. The red arrow shows strandings in Laguna San Ignacio, Baja California Sur, Mexico. Illustration: NOAA Fisheries


A gray whale found dead off Point Reyes National Seashore in northern California. Photo by Barbie Halaska.


More than 380 gray whales have been found dead along the Pacific coasts of Mexico, USA, and Canada. A recent scientific article published in January suggests starvation may be the underlying cause of the 2019-2020 gray whale UME. Two authors of this article, Jorge Urbán R. and Steven Swartz, discussed their research which is available in Saving Ocean Wildlife’s March 17th webinar, “Why are our Gray Whales Dying?”

About gray whale research at LSIESP

Research Focus for Winter 2021

Previous surveys of gray whales in Laguna San Ignacio and Bahía Magdalena in 2019 and 2020 documented the second successive year of low calf production, and a decrease in the number of female-calf pairs utilizing the lagoon. Photographic identification documented a significant increase in the percent of “skinny undernourished” adult whales suggesting decreased food availability in the summer feeding areas. AUV-Drones with HD-video are used to measure gray whale calf growth, female weight loss, and adult nutritive condition to facilitate evaluation of health and reproductive condition of whales during periods of food resource limitation, and possible stress from other environmental factors (e.g., climate change, eco-tourism).

Research Background

In response to the late arrival of the whales to the lagoon aggregation areas (approximately two weeks from previous winters), extremely low calf counts, and a significant increase in “skinny” whales (from < 7% in previous years to 27% in 2019, and 30% in 2020), our immediate goal in 2021 is to shift our research focus to monitoring the response of gray whales to possible food limitation and disease, and to utilize abundance surveys, photographic-Identification surveys, and AUV-Drone measurement of whale body condition and reproductive condition in the lagoons to document:  1) arrival and departure times of the whales to and from the lagoons; 2) levels of abundance compared to previous years; calving rates (intervals); 3) calf growth rates; whale body condition and 4) health; and movements between lagoon areas. This information will allow ongoing monitoring and evaluation of the response of the whales to climate driven conditions and changes in the availability of sufficient food in the summer months.

How you can make a difference

Report a Stranded or Floating Whale

The most important action someone can take is to immediately report a dead, injured, or stranded marine mammal. Make the report by calling in California, Oregon or Washington the West Coast Marine Mammal Stranding Network: 1-866-767-6114, in Alaska the Alaska Marine Mammal Stranding Network: 1-877-925-7773, and in Canada, the British Columbia Marine Mammal Response Network: 1-800-465-4336.  

You can also contact the U.S. Coast Guard on VHF Channel 16. Do not approach or touch injured or dead marine mammals.

All marine mammals are federally protected by the Marine Mammal Protection Act. Only local and state officials and people authorized by NOAA Fisheries may legally handle live and dead marine mammals.

Contribute to the UME Contingency Fund

The Marine Mammal Unusual Mortality Event Contingency Fund is used to help the marine mammal stranding network investigate and respond to UMEs. You can donate to the UME Contingency Fund through Pay.gov and help cover costs incurred by the Marine Mammal Stranding Network while investigating UMEs.

Join Saving Ocean Wildlife for this webinar

To learn more about the 2019-2020 gray whale UME and how you can get involved, join us on March 17, 2021 from 7-8 PM PDT for the webinar by Jorge Urbán Ramírez and Steven Swartz. Click here to register for the webinar.

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