Scientists finally figure out why hundreds of gray whales keep washing up dead along US coasts

A dead grey whale (Eschrichtius robustus) on the beach near the town of San Juanico in Baja California Sur, Mexico. (Image credit: CampPhoto via Getty Images)

A strange series of mass deaths among gray whales in the northeastern Pacific Ocean may finally have an explanation, with scientists linking Arctic sea ice levels to the major die-off events. 

Three mortality events have struck gray whales (Eschrichtius robustus) living off the coast of North America since the 1980s, reducing the population by 15% to 25% each time, according to a new study. In total, more than 2,000 gray whales are known to have died. The first mass die-off took place between 1987 and 1989 and was the largest in magnitude, killing at least 700 whales. Reporting structures and survey efforts only expanded in the 1990s, however, meaning the number of strandings associated with this mortality event could be an underestimate, according to the study. The second took place between 1999 and 2000, killing 651 whales

The latest die-off began in 2019 and saw more than 70 gray whales wash up dead in just six months. It is ongoing and — as of Sept. 26, 2023 — a total of 688 whales have died. What caused each of the events was unclear. 

"These are extreme population swings that we did not expect to see in a large, long-lived species like gray whales," study lead author Joshua Stewart, an assistant professor at Oregon State University's Marine Mammal Institute, said in a statement.

Related: Could an impending rise in solar storms cause more whales to strand?

Commercial whaling until the mid-20th century drove the population of North Pacific gray whales to near-extinction, but it has since bounced back and currently numbers around 14,500 individuals, according to the statement. Scientists previously thought this successful recovery meant the whales were dying off periodically as their numbers exceeded what their habitat and prey could provide for.

But changing conditions and fluctuating sea ice levels in the Arctic may better explain what the National Oceanic and Atmospheric Administration (NOAA) termed "unusual mortality events," according to the new study, published Oct. 12 in the journal Science.

Sea ice cover and the amount of food available for gray whales may dictate how the population fares. Higher-than-usual ice cover in some years may block passage to the Bering and Chukchi seas, where the whales spend the summer months feasting on fatty crustaceans before migrating southward again. "When the availability of their prey in the Arctic is low and the whales cannot reach their feeding areas because of sea ice, the gray whale population experiences rapid and major shocks," Stewart said.

Gray whales quickly rebounded from the first two mortality events. But the most recent die-off is ongoing since 2019 and has cast us into "uncharted territory," Stewart said. 

Unlike the two previous events, a historic loss of Arctic sea ice could be to blame for the latest gray whale die-off. That's because sea ice hosts a carpet of algae on its underside, which decays and showers the seabed with food for bottom-dwellers, including the whales' preferred crustaceans. 

"With less ice, you get less algae, which is worse for the gray whale prey," Stewart said. Melting sea ice also frees up passage for strong currents that sweep away the sediment and leaves bottom-dwelling crustaceans and other creatures homeless. "All of these factors are converging to reduce the quality and availability of the food [gray whales] rely on," he said.

Climate change might be the reason this mortality event is dragging on for longer than the previous two, Stewart said. "What we're seeing is much more of a bumpy ride in response to highly variable and rapidly changing ocean conditions," he said.

While climate change could mean there is less food for gray whales, it probably won't put the northeastern Pacific population at risk of extinction, Stewart said. But "an Arctic Ocean that has warmed significantly may not be able to support 25,000 gray whales like it has in the recent past," he added.

Sascha Pare
Trainee staff writer

Sascha is a U.K.-based trainee staff writer at Live Science. She holds a bachelor’s degree in biology from the University of Southampton in England and a master’s degree in science communication from Imperial College London. Her work has appeared in The Guardian and the health website Zoe. Besides writing, she enjoys playing tennis, bread-making and browsing second-hand shops for hidden gems.

  • syduser
    What a load of rubbish
    Look up US and foreign navy use of active sonar
    The ocean is literally filled with submarines and sonar buoys letting out acoustic pollution via active sonar that is so intense it makes the sea boil in the immediate vicinity of the buoy/sub and is strong enough to physically destroy tissue of living creatures for kilometres.

    In some cases hundreds of kilometres depending on the nature of the ping (yes, these are some of the loudest sounds on planet earth and water carries sound far better than air).

    It's not widely discussed because the navy/military is allowed to suppress any press coverage of its methods and operations.

    Such an ambivalent news article filled with such tepid assertions backed by bogus science is nothing more than fear mongering when extremely likely alternatives exist that present far more credible evidence.

    Whales have bodies susceptible to such acoustic pollution, migrate through corridors where such measures are used intermittently and use sound to communicate (which means they could not only be injured by the sound but also rendered unable to communicate properly with their pod).
  • mad titan
    admin said:
    Three mass mortality events have struck a population of gray whales off the west coast of North America since the 1980s, and scientists have linked them to changing conditions in the Arctic.

    Scientists finally figure out why hundreds of gray whales keep washing up dead along U.S. coasts : Read more
    What scientists exactly figured this out? Also, if the answer was so elementary why are scientists so stupid to not have figured that out eons ago? I'm sorry, but I really don't think there's enough stupid people on this planet that would actually believe this level of ignorance with ZERO proof or even a source.... I truly feel sorry for the writers generation. These poor kids are gonna give themselves a stroke over fake outrage at a very young age lol.
  • forbes1114
    Why isn't the media talking about all the nuclear waste Japan has been dumping in our oceans. Maybe that has something to do with it. Washington has the highest cancer patients in the world. Only cause all that radio active water gets thrown along the united States west coast. And they are still dumping 30 thousand gallons a day into the ocean. And where does rain come from, our oceans and when it rains all that rain is radio active. And nobody has a clue. Haven't u noticed the rain gives u a tingly feeling now these past few years. It's cause it has finally made it to our coast in full force.
  • OneHoop
    Yes, @syduser , I also wondered why this article did not mention military sonar. Loss of habitat may lead to population fluctuation, but mass die-offs of this scale are hard to imagine as a result.
  • balawea
    syduser said:

    OneHoop said:
    Yes, @syduser , I also wondered why this article did not mention military sonar. Loss of habitat may lead to population fluctuation, but mass die-offs of this scale are hard to imagine as a result.
    Habitat loss is literally the leading cause of species extinction worldwide. That's about as big a die-off as you can get.,noise%20pollution%20are%20some%20examples.
  • Rose4U
    Conveniently they completely ignore Canada's lax sea dumping regulations, sending all kinds of toxic waste in horrifying amounts posing catastrophic consequences to the oceans deep & fragile ecosystem. Causing the death of killer whales and many more precious & vital species the earth relies on for healthy balance. Just blame everything on this concept the globe is changing completely due to mankind when the earth has been forever changing whether we're here or not. People are definitely damaging the planet, but this notion we brought this on entirely can not be assumed considering the earth has always had its own evolutionary process forever changing. It actually rather arrogant & audacious to assume it should never change & be to our liking simply because we have graced it with our presence! I resent the fact that this is more corrupt promotion of the climate agenda pushers to the extent they blatantly deny & staunchly ignore & defiantly refuse to expose other elements destroying the planet such as a country's deliberate efforts to ruin the oceans via way of sewage dumping & chemical waste the "respected" Canadian govt is permissing while no other nations are calling them out for it & holding accountability. If they are so concerned with the planet then see it as your responsibility and sanction them until they comply with modern standards & made to clean it up and fined/imprisoned. This hogwash about the climate obsessed, (when I was a child it was the ozone layer hole), while they turn a blind eye to a first world country's deplorable acts of war against our earths most important resource, our oceans, it's too absurd to comprehend. This article was an agenda piece written for just that objective, suggesting no other possibilities including obvious deadly pollution first world govts are guilty of & allowing ships to empty out once they are in Canadian waters. This could definitely be a direct result of such abuse of our planet. Please focus on other earthly concerns rather than just your money grubbing "climate change" this & "climate change" that. Some disturbing loss & unforgivable phenomenon could easily be explained by our govts actions but that exposes them as frauds & evil criminals on grand scale. You can not put a price on our wild species & all the organisms needed on this planet. An everyone & everything has its purpose. Someone mentioned Japan and their violations and they are monsters, the crimes they do to dolphins and those Asian countries are notorious for funding species extinctions. There are many other driving factors to mass death, it's not always "Just Climate Change". Big business that climate change is that it gets full credit these days like nothing else is wrong here that man is doing!?!