Sascha Pare
Tue, October 17, 2023
A beached gray whale in Baja California Sur in Mexico.
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.
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"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.
Scientists may have finally decoded mystery behind whales washing up dead along Pacific coast
Vishwam Sankaran
Tue, October 17, 2023
Changing Arctic ice cover and prey availability are the reasons behind gray whales washing up dead along the Pacific coast since 2019, according to a new study.
Scientists have been perplexed by the surge of gray whale strandings since 2019 with estimates suggesting that the mammal’s population in the North Pacific have declined from a peak of around 27,000 in 2016 to about 14,500 in 2023.
“These are extreme population swings that we did not expect to see in a large, long-lived species like gray whales,” Joshua Stuart from Oregon State University’s Marine Mammal Institute said in a statement.
“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,” Dr Stuart, author of the new study published in the journal Science, said. The study sheds light on the impact of climate change on these marine mammals.
The new research revealed that even highly mobile, long-lived species like gray whales are sensitive to climate change impacts.
Eastern North Pacific gray whales are one of the few populations of large whales in the world that have recovered to levels similar to those that existed prior to commercial whaling – making it a conservation success story in the post-whaling era.
Their population, which currently numbers about 14,500, migrate over 19,000km (12,000 miles) each year along the Pacific Coast – from the warm waters off the coast of Baja California, Mexico, in winter to the cold waters of the Arctic to feed during summer.
They are also the most closely studied large whale population on the planet, offering unique insights into factors affecting the species.
Researchers found from long term observation that unfavourable Arctic conditions led to two previous die-offs of these whales in the 1980s and the 1990s, which were not permanent as the population quickly rebounded with improved conditions.
But when a large number of gray whale strandings began occurring along the Pacific coast in 2019, scientists were perplexed about what was driving this latest unusual mortality event.
Now, by combining long-term data sets on the gray whale population with extensive environmental data from the Arctic, researchers found that the two “Unusual Mortality Events” in 1999 and 2019 are tied to sea ice levels in the Arctic and the biomass of seafloor-living crustaceans that the whales target for food.
They say years with less summer sea ice in the gray whales’ Arctic feeding areas provided increased foraging opportunities that benefited the population.
However, in the long term, decreasing sea ice cover due to rapid and accelerating climate change may not be beneficial to gray whales, scientists warn.
Deep sea shrimp-like crustaceans called amphipods which are the calorie-rich prey that gray whales prefer, are sensitive to sea ice cover, researchers say.
The amphipod population, according to scientists, is enriched by algae that grow underneath sea ice as it sinks to the seafloor.
But less ice leads to less algae reaching the seafloor, researchers warn.
They say warmer water also favors smaller deep sea crustaceans as well as faster currents that reduce habitat for gray whales’ preferred prey.
“With less ice, you get less algae, which is worse for the gray whale prey. All of these factors are converging to reduce the quality and availability of the food they rely on,” Dr Stuart explained.
Less prey availability ultimately leads to gray whale die-offs such as in the most recent event, which is is still considered ongoing, continuing significantly longer than the two earlier events.
“We are in uncharted territory now. The two previous events, despite being significant and dramatic, only lasted a couple of years,” Dr Stewart said.
“The most recent mortality event has slowed and there are signs things are turning around, but the population has continued to decline. One reason it may be dragging on is the climate change component, which is contributing to a long-term trend of lower-quality prey,” he added.
Gray whales have been mysteriously washing up dead on the Pacific coast. Now scientists think they might have the answer.
Kelsey Vlamis
Mon, October 16, 2023
Gray whales have been dying off at an alarming rate since 2019.
Scientists at Oregon State think the deaths could be due to melting sea ice, a new study says.
The melting ice may be causing a decrease in the crustaceans the whales prey on.
Gray whales have been washing up dead on the Pacific coast at an alarming rate since 2019, and scientists think they might finally know why.
The gray whale strandings from Mexico all the way to Alaska have been declared an "unusual mortality event," or a significant die-off of a species that is unexplained and requires a quick response.
Two other mass die-offs of gray whales occurred in the 1980s and 1990s, though those only lasted a couple of years; the latest is still ongoing.
The latest die-off has caused the North Pacific gray whale population to plummet from an estimated 27,000 in 2016 to 14,500 in 2023, according to the National Oceanic and Atmospheric Administration.
For years, researchers could only guess what was killing the whales. NOAA has previously noted that emaciation had been observed in some of the dead whales, but not in others.
But scientists at Oregon State University's Marine Mammal Institute now say there is strong evidence that the whale deaths are linked directly to sea ice melting in the Arctic, according to a study published Thursday in the journal Science.
Joshua Stewart, an assistant professor at the Marine Mammal Institute and lead author of the study, said the decrease in sea ice was also causing the gray whales' food supply to diminish.
"Feels like this time we've got a pretty good 'smoking gun," Stewart told the outlet KTVB of the explanation of what was causing the whale deaths.
Gray whales make the longest migration of any mammal on Earth, traveling more than 12,000 miles every year from their foraging grounds in the Arctic, where they spend the summers, to their breeding grounds in the warm, shallow lagoons of Mexico's Baja Peninsula, where they spend the winters.
While in the Arctic, the gray whales feed on amphipod crustaceans. Amphipods in turn feed on algae, which grows on the underside of sea ice.
"With less ice, you get less algae, which is worse for the gray whale prey," Stewart said in a release from Oregon State, adding, "When there are sudden declines in the quality of prey, the population of gray whales is significantly affected."
In other words, the melting sea ice disrupts the entire food chain.
The decrease in available food can cause skinnier or malnourished whales, as well as lower birth rates. Stewart said he does not think there is currently a risk of extinction for gray whales. The species, which was hunted to the brink of extinction decades ago, has been touted has a major conservation success thanks to the populations bouncing back after international whaling regulations were enacted.
But the die-offs are a reminder of the wide-ranging impacts of the climate crisis, as sea ice continues to melt at alarming and historic rates.
"Even highly mobile, long-lived species such as gray whales are sensitive to climate change impacts," Stewart said.
And while he said we probably do not have to worry about extinction, we may have to simply get used to having fewer gray whales.
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