Pacific Gray Whale Population Drops by Nearly 25%
Being taken off the endangered species list sadly doesn’t guarantee a carefree future for whales. Recent research estimates that the population of Pacific gray whales off North America’s West Coast has declined by almost a quarter since 2016. These whales are known for the epic migrations between their Arctic feeding grounds and the breeding lagoons in Mexico’s Baja Peninsula, a migration route that takes them very close to land and makes them easy to see from shore almost anywhere along the West Coast.
Starting in 2019, alarming numbers of dead gray whales were spotted on beaches and floating offshore throughout their habitat, from Mexico to Alaska. There were so many whales that the National Marine Fisheries Service (NMFS) declared an “Unusual Mortality Event” for gray whales. UMEs are declared when a “significant die-off” occurs in any marine mammal population, and directs additional resources to collect information in hopes of understanding why the die-off is occurring. Marine mammals are sentinels of ocean health, so when they are sick or dying in high numbers, it can be a sign that something is wrong with their ocean ecosystem.
Although the cause of the current gray whale UME is still unknown, researchers believe it is most likely due to starvation from a lack of adequate prey on the whales’ Arctic feeding grounds. Gray whales are baleen whales and feed on a variety of small invertebrates, especially amphipods (tiny shrimp). Like other long-distance migrators, they don’t feed on their winter breeding grounds or along their migration, and must bulk up during the summer to sustain themselves through the rest of the year.
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The Arctic has had historically low levels of sea ice in recent years, upending the delicate ecosystem that sustains gray whales and many other species. Observers using aerial photography to assess body condition in gray whales noted the whales looked skinnier starting in 2018, and that they were arriving in Mexico in poor condition, which suggested they were not finding enough food during the summer.
This die-off of gray whales is alarmingly similar to the events of 20 years ago, when another UME resulted in a significant drop in the gray whale population. Although the cause of that UME was ultimately undetermined, it’s thought that the population reached “carrying capacity” – it grew too large for the environment to support it. Although that idea has been suggested for this die-off as well, it’s more likely due to the changing conditions of the Arctic.
Gray whales were hunted almost to extinction by the mid-20th century. Their close-to-shore habitat, which makes them a delight for whale watchers, also made them easily accessible for West Coast whalers. Along with North Atlantic right whales, they were one of the first whales to be protected from hunting. The Eastern North Pacific population rebounded without pressure from whaling, and was taken off the U.S. Endangered Species List in 1994; the Western North Pacific population is still listed as endangered. However, new threats have arisen for gray whales with increasing human use of their habitat, including vessel strikes, accidental entanglement in fishing gear, noise, and effects from climate change.
418 gray whales have been found dead since 2019 as of March 8th, 2021. Many more have certainly died, since the majority of whale carcasses sink or float out to sea and are never spotted by humans, and survey efforts have been impacted by limited response ability during the COVID-19 pandemic. The annual census of gray whales counted 6,000 fewer migrating whales last winter compared to 2016, leading to the estimate that the population has dropped by a quarter in recent years.
A unique group of gray whales known as the Pacific Coast Feeding Group (PCFG) don’t go back to Arctic waters to forage, but stay off the coast between Northern California and Southeast Alaska. Another group known as the Sounders makes a “pit stop” in Puget Sound along their migration to feed on ghost shrimp – a strategy that may have given them an advantage during this recent die-off.
This news is alarming, especially because strandings remain higher than “normal” in 2021. It is a reminder that being taken off the official Endangered Species List does not mean that a population’s future is secure. New threats arise, climate change upends habitats, and continued monitoring and work is needed to make sure whales can fulfil their role as essential parts of our global ecosystem.
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