Gray whales migrating along the west coast of North America have continued to decline over the past 2 years, according to a new assessment from NOAA Fisheries. The population is now down 38% from its peak in 2015 and 2016, as researchers search for the underlying reasons. The population also produced the fewest pups on record this year since counts began in 1994, the report explains.
The 38% decline from a peak of about 27,000 whales in 2016 to 16,650 this year reflects past fluctuations in the eastern North Pacific population. “Given the continuing decline in numbers since 2016, we need to closely monitor the population to help understand what may be driving the trend,” said Dr. David Weller, director of the Division of Turtles and Marine Mammals in the Division of Sea mammals.
An increase in gray whale strandings led NOAA Fisheries to declare an Unusual Mortality Event (UME) for the population in 2019, prompting an investigation into the likely causes. These include ecological changes in the Arctic that affect the seabed and the amphipods and other invertebrates that live in and above the sediment and in the water column, which gray whales feed on each summer, according to new research published today.
Some gray whales may have had trouble finding food amid those changes, said Dr. Sue Ellen Moore, a University of Washington researcher who leads the team assessing ecological influences. She noted that gray whales feed on a wide variety of prey over a wide range, so there could be a lot of variables that affect how, when and where they find food.
While many of the roughly 600 recorded dead whales between 2019 and 2022 appeared malnourished, some were not. Some stranded whales had clearly died of other causes, such as being struck by ships or predation by killer whales. The number of strandings initially spiked in 2019, but then declined in subsequent years. That suggests that most of the gray whale population decline likely occurred in the years after an HEU was declared.
“There’s nothing we can point to that explains all the strandings,” said Deborah Fauquier, Veterinary Medical Officer in NOAA Fisheries’ Marine Mammal Health and Stranding Response Program, who is coordinating the UME investigation. “It appears that there are multiple factors that we are still working to understand.”
Gray Whales are known for their visible migration along the West Coast each year. The population has fluctuated much before, including a similar drop of around 40% from the late 1980s to the early 1990s. The population later recovered to a new high point. Gray whales in the eastern Pacific Ocean fully recovered from the days of commercial whaling and were removed from the endangered species list in 1994.
A similar increase in strandings led to the declaration of an earlier Unusual Mortality Event in 1999 and 2000, when the population declined by approximately 25%.
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