SEATTLE (AP) — U.S. researchers say the number of gray whales off western North America has continued to fall over the last two years, a decline that resembles previous population swings over the past several decades.
According to an assessment by the National Oceanic and Atmospheric Administration Fisheries released Friday, the most recent count put the population at 16,650 whales — down 38% from its peak in 2015-16. The whales also produced the fewest calves since scientists began counting the births in 1994.
An increase in the number of whales washing up on West Coast beaches prompted the fisheries agency to declare an “unusual mortality event” in 2019. Researchers are still investigating the die-off, but they say climate change and its effects on sea ice and prey availability and location are likely factors. Many, but not all, of the whales that washed up appeared malnourished.
The population recovered from the days of commercial whaling before a similar population drop of 40% occurred in the late 1980s and early 1990s. Gray whales were removed from the endangered species list in 1994.
The population rebounded before a spike in whales washing up on beaches prompted the declaration of another “unusual mortality event” in 1999 and 2000, when the number of whales fell by a quarter.
“We've been monitoring the population since the 1960s. So we've seen those two big drops and they've recovered each time. So I think it is, at least in part, a natural phenomenon,” said Aimee Lang, a research biologist with NOAA Fisheries Southwest Fisheries Science Center in San Diego. She led the field team that collected the counts in this most recent assessment.
She said it’s not possible to pinpoint a cause of the current die off and multiple factors are likely involved, though ecological changes in the Arctic are probably a leading factor.
“I think what we kind of don't know is how some of these ecological changes in the Arctic, if they're happening faster and faster, what sort of impact that's going to have,” Lang said.
Her team agrees that although the current population swing so far fits within historical patterns, it's nevertheless concerning.
"We need to be closely monitoring the population to help understand what may be driving the trend,” said David Weller, director of the Marine Mammal and Turtle Division at the Southwest Fisheries Science Center in San Diego.
Researchers count the whales as they return from their summer feeding grounds in the Arctic to the Baja Peninsula lagoons where they nurse their calves in the winter. Typically, the counts are conducted over a two-year period, but to better monitor the population, NOAA Fisheries is adding a third year to the current survey, counting the whales as they pass the central California coast from late December to mid-February 2023.
The calves are counted as the whales head north to the Artic. There were 217 calves in the count that finished in May, down from 383 the year before.
Biologist John Calambokidis, with Cascadia Research in Olympia, calls the new census from NOAA Fisheries “sobering.”
But he views gray whales as remarkably resilient – and agreed with NOAA’s reminders of the context that their population numbers have seen tremendous fluctuations in the past.
“The gray whale population did bounce back surprisingly effectively from that mortality about in the late 1990s, early 2000s,” Calambokidis said.
And he has documented how adaptive gray whales are. Every year, a group called the Sounders takes a detour from the coast to feast on ghost shrimp in Puget Sound.
“And we think the Sounders just represent, you know, one of a number of alternate feeding strategies that gray whales might use,” he said.
He said other gray whales have been seen looking for food in stops all along the west coast, from Los Angeles Harbor to Southeast Alaska. They’re not always successful, but in the years since he first started researching the Sounders, their numbers have nearly quadrupled.
