NOAA Fisheries is declaring an unusual spike in strandings of gray whales along the West Coast an Unusual Mortality Event (UME), providing additional resources to respond to the strandings and triggering a focused scientific investigation into the cause.
As of this week, more than 60 gray whales have stranded on the coasts of California, Oregon, Washington, and Alaska this year, the most since 2000 when more than 100 whales stranded throughout the year. NOAA Fisheries also declared a UME at that time but the resulting investigation did not identify a specific cause.
The Marine Mammal Protection Act (MMPA) defines a UME as a stranding event that is unexpected, involves a significant die-off, and demands immediate response. Given the increased strandings, NOAA Fisheries convened a UME Working Group of marine mammal experts to assess seven criteria to determine whether a UME should be declared, as outlined in the MMPA.
The working group members include experts from scientific and academic institutions, conservation organizations, and state and federal agencies who work closely with stranding networks and have a wide variety of experience in biology, toxicology, pathology, ecology, and epidemiology.
In this case, the UME Working Group determined that the gray whale strandings this year meet two of the seven criteria:
- a marked increase in the magnitude or a marked change in the nature of morbidity, mortality or strandings when compared with prior records; and
- similar or unusual pathologic findings in stranded animals, including behavior patterns, clinical signs, or general physical condition such as blubber thickness.
The population of eastern North Pacific gray whales has recovered from the whaling era and were removed from the endangered species list in 1994. The population remains protected under the MMPA and has grown considerably in the last decade, now numbering about 27,000. Gray whales in the western North Pacific remain endangered.
Each spring eastern North Pacific gray whales migrate 10,000 miles or more along the West Coast from winter waters in Mexico where they give birth to summer feeding grounds in the Arctic off Alaska.
The whales rely largely on their summer feeding in the Arctic to last them throughout the year because they do not feed extensively while migrating or wintering in Mexico. Many gray whales that have stranded this year during their northbound migration have been skinny and malnourished, with some showing signs of emaciation.
That suggests that some whales may be exhausting their energy reserves this year before they reach the Arctic to resume feeding, researchers say.
Growing wildlife populations can bring more mortalities simply because there are more animals overall. Larger populations can also lead to additional competition for or depletion of food, which may increase the rate of mortalities. An analysis by the UME Working Group found that the rate of gray whale strandings this year relative to the size of the population is above the average of recent years, which is further evidence that a UME is occurring.
A UME declaration focuses the additional scientific expertise of the UME Working Group’s members on the possible causes of the strandings. The determination also makes more resources available to NOAA Fisheries’ West Coast Marine Mammal Stranding Network and Alaska Marine Mammal Stranding Network to respond to the continued strandings, which have occurred on an almost daily basis this spring.
NOAA Fisheries will coordinate the investigation with international partners in Canada and Mexico, as well as with state wildlife agencies and our stranding network partner organizations. The investigation and research will likely continue as long as the UME lasts. Updates on the investigation will be posted on a dedicated UME website.