Gray whale perils align, causing spike in deaths
A troubling dieoff of gray whales along the Pacific Coast two years ago appears to have continued through 2020, raising concerns that the celebrated rebound of the ocean giants might not be a sure thing.
The whales, once hunted to nearextinction, are dying from a combination of killer whale attacks, ship strikes and starvation. Scientists aren’t certain why these perils have lined up to create a sharp spike in deaths, but they believe it’s tied to disruptions in ocean conditions wrought by climate change.
As the whales swim past California this winter, on an unparalleled migration between the Arctic and Mexico, marine biologists are watching to see if the worrisome trend holds for another year. Some fear that the ocean changes pose an everincreasing challenge for the cherished titan and could mean a longtime drag on its future.
“We may have a few years where the mortality levels are less,” said Pádraig Duignan,
chief pathologist at the Marine Mammal Center in the Marin Headlands, who has been performing necropsies of the whales. “But I expect to see events like this happening at greater frequency than we did in the past.”
In 2020, 172 whales were found washed up on beaches along the West Coast of North America, according to figures from the National Oceanic and Atmospheric Administration. Seventynine were in the United States, 88 were in Mexico and five were in Canada. The numbers were only slightly down from the total 214 counted in 2019.
While a few beached whales is common during the cetacean’s annual migration, the recent numbers are not normal. For every whale that is found dead, scientists estimate there are five to 10 more that die unnoticed. Most sink to the bottom of the ocean or decompose without making landfall.
In 2019, when the uptick in deaths was first observed, the National Oceanic and Atmospheric Administration declared an “Unusual Mortality Event,” a designation that directed money and researchers toward the problem. An investigative team of federal and academic scientists continues to try to learn more about why the whales are dying.
Gray whales were once prevalent across the Northern Hemisphere. Today they’re found in just two distinct populations: one small group along the coasts of China, Korea and Russia, and the rebounding group that travels up and down the West Coast each year.
Both populations were on the brink of extinction a century ago, but international protections and a ban on commercial whaling are credited with saving the species. The North American group is believed to have since swelled to nearly 27,000 animals. The 50foot beasts, which can weigh 90,000 pounds and live for 80 years, have become a popular spectacle for Bay Area coastgoers.
The concern, though, is that increasing disruption to the ocean environment could undo the decades of progress.
“When changes start happening to populations, they can happen dramatically and quickly,” Duignan said. “The whales are doing well now, but if something more drastic happens, then the population could crash.”
Observations and necropsies conducted by Duignan and other scientists reveal a handful of causes of death for the whales. However, poor nutrition often underlies the animal’s condition, and if it didn’t cause the demise, it sometimes contributed to it.
For example, when a gray whale succumbs to a killer whale, it could be that the whale wasn’t healthy enough to defend itself or its calf, Duignan said. A collision with a ship could be the result of a whale having to go to new places to find food, like San Francisco Bay, where they’re apt to encounter more human activity.
Most of the observations and necropsies done by the scientists were conducted in 2019. The coronavirus pandemic limited the research and collaboration last year. But those involved in the work say their thinking remains the same: The whale’s poor health is likely linked to stress resulting from the climatealtered ocean.
The biggest problems are in the Arctic, where the whales spend their summers feeding.
There, they rely on shrimplike crustaceans known as amphipods, which they eat off the ocean floor. These amphipods, however, may be becoming
less numerous and less nutritious. The algae that the amphipods eat, which grow on sea ice before falling to the ocean bottom, are becoming scarcer as the ice retreats amid warming temperatures. Consequently, the amphipods aren’t as robust, and the whales aren’t getting the meals they’re used to.
Higher ocean temperatures in the Pacific have also changed the distribution of the whale’s other prey, which include plankton, ghost shrimp and crab larvae, and fish that share their prey, both of which affect a gray whale’s diet.
“Warmer waters are just generally not good for productivity,” said Sue Moore, a research scientist at the University of Washington who studies whales in the Alaskan Arctic and is part of the team investigating the dieoff. “The ( new) prey may have less fat, it may be less nutritious. The whale’s body condition is going to start showing signs of that, and if they’re a female, they may not be able to bring a calf to term.”
The weakened state of the whales also makes them more susceptible to disease, Moore said.
“Is this enough to kick the ( mortality) event off? I don’t know,” she said.
Fortunately, the whales are highly resilient, Moore added.
They’re able to shift to new food sources and alter their migrations to seek out food. This is helping them withstand the changing ocean and persevere on their 10,000mile roundtrip that brings them back to the lagoons of Baja California, where they give birth and spend part of the winter.
The dieoff is eerily similar to an uptick in whale deaths two decades ago. In 1999 and 2000, more than 600 beached whales were reported on the West Coast, with scientists estimating that 20% of the total gray whale population was lost. In 2001, however, the numbers stabilized, and there hasn’t been a significant drop until now.
John Calambokidis, a senior research biologist at the Cascadia Research Collective in Olympia, Wash., and part of the team investigating the whale deaths, says the current episode could be just another correction in the population.
“There are still many mysteries about why we saw such a dramatic surge in mortality,” he said. “If we see a continuation of mortality in 2021, then I will start to become more concerned — and potentially alarmed.”