Grey whales are starving to death in the Pacific and scientists don’t know why
- Thirty-one dead grey whales have been spotted along the US west coast since January, the most for this time of year since 2000
- Death toll expected to climb through May as the animals continue their annual migration from Mexico to their icy feeding grounds in the Arctic
From Baja California to Puget Sound, scientists are seeing signs that grey whales are in distress. And they have no idea why.
Thirty-one dead grey whales have been spotted along the west coast of the US since January, the most for this time of year since 2000, when 86 whales died. Dozens more have shown visible signs of malnourishment, and sightings of mother-calf pairs are down sharply.
The grey whale death toll will probably climb through May as the animals continue their annual migration from their warm breeding lagoons in Mexico to their icy feeding grounds in the Arctic, said Justin Greenman, the assistant coordinator of stranded marine mammal response in California for the National Oceanic and Atmospheric Administration.
Experts said that, with about 27,000 grey whales thriving around the world, this year’s deaths probably do not present a serious threat to the species. But the casualties cannot be ignored, either.
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“It’s not like we’re ringing the alarm bell that this population is threatened or at risk,” said John Calambokidis, a biologist and co-founder of Cascadia Research who tracks grey whales in Washington state. “As a researcher, I feel that you want to at least understand what is going on.”
So far, scientists know little more than what they can see. They have documented 21 dead whales that have turned up in Long Beach, Los Angeles, San Francisco Bay and elsewhere on California shores. Most of them had not yet reached adulthood and looked like they might have starved to death.
Frances Gulland, a research associate at the University of California, Davis School of Veterinary Medicine, estimates that grey whale deaths could hit 60 or 70 by the end of the season.
“If this continues at this pace through May, we would be alarmed,” she said.
In a typical year, scientists at the Marine Mammal Centre in Sausalito see two or three dead grey whales. So far this year, they have counted seven, according to Padraig Duignan, the centre’s chief pathologist.
Duignan performed necropsies on all of them and determined that four had died of malnutrition.
“Their skeleton seems to stick out more and more,” he said.
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Emaciated whales are also turning up with greater frequency along the west coast. These whales are more angular in appearance, and have less muscle mass behind their heads.
Steven Swartz, a marine scientist who studies grey whales in Baja California’s San Ignacio Lagoon, said 23 per cent of the whales without calves his team has observed this year were skinny. That percentage is more than three times higher than usual.
And then there’s the missing calves.
In San Ignacio Lagoon, researchers typically see at least 75 mother-calf pairs each year. This year, they’ve seen only about 40, Swartz said, though none of them appeared to be unusually thin. Calf sightings typically peak in March and early April.
Off the coast of Los Angeles, observers working with the American Cetacean Society have counted 31 grey whale calves migrating northward since December 1, said marine biologist Alisa Schulman-Janiger. Over the past decade, the number of northbound calves seen by this time of year has ranged from 28 to 164.
Giving birth requires lots of energy and blubber, and thin whales are in “no condition to be nurturing pregnancy or a calf”, she said.
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Scientists said they suspect the grey whales are malnourished because they did not eat enough in the North Pacific and Arctic last summer – a time typically spent packing on as many calories as possible and building up reserves for their journey to Baja California and back.
But it is too soon to pinpoint the causes, or to know whether it is the beginning of a more permanent trend, said Elliott Hazen, a research ecologist with NOAA’s Southwest Fisheries Science Centre in Monterey, California.
Researchers cannot even tell if it is a problem of supply or demand.
Whether it’s not enough prey, too many whales, issues with the habitat – that is what we are currently investigating
“Whether it’s not enough prey, too many whales, issues with the habitat – that is what we are currently investigating,” Greenman said.
Adding to the mystery is the fact that other whale species do not seem to be affected, he added.
Researchers at NOAA’s Alaska Fisheries Science Centre plan to study when and where grey whales feed in the Arctic to help them understand whether prey has become more scarce. NOAA researchers on the west coast are currently surveying the number of calves migrating north, and in the fall they intend to count the number of grey whales that migrate south, including calves.
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Scientists also have much to learn about the small crustaceans and other animals grey whales rely on for food. For instance, they think declines in Arctic sea ice or other ecological changes could be making prey more scarce.
In 2013, researchers spotted an area of warm water off the Gulf of Alaska, and that might be part of the problem. “That warm water layer – called ‘the blob’ or marine heatwave – had a number of ecosystem effects we’re still trying to disentangle,” Hazen said.
Other factors, like illness, can also prevent whales from eating as much as they should. “That’s a mystery that’s still being unravelled,” he said.
“We are concerned because whales are an indicator species for the health of the ocean,” Duignan said. “We use them to tell us what’s happening out there.”
