The stranding of 70 gray whales along the United States' west coast is considered to be an "unusual mortality event" by the the National Oceanic and Atmospheric Administration (NOAA) Fisheries.
Thirty-seven gray whales have washed up in California, including more than a dozen in the San Francisco Bay Area, experts said during a NOAA conference call on Friday afternoon. The whale species have also been beached in Oregon, Washington and Alaska.
Five gray whales have also beached in Canada, according to Michael Milstein, public affairs officer for NOAA Fisheries' west coast regional office.
There are currently an estimated 27,000 gray whales that migrate in the eastern northern Pacific region, incliuding 1,600 calves, according to the NOAA, which cited a 2016 survey. This population estimate is considered to be "abundant" and "on par" with the estimates from 1987 to 1988, when there were 26,900, said Dave Weller, research wildlife biologist for the Southwest Fisheries Science Center in La Jolla, California.
The gray whales had a poor feeding season during summer and fall 2018
Researchers are trying to figure out whether the elevated die-offs are occurring due to environmental factors, disease or human activities, such as ship strikes, said Deborah Fauquier, veterinary medical officer for NOAA Fisheries. Once they narrow it down, scientists will then determine a response plan.
Lately, the whale population has been "subpar and less energetic," perhaps due to a poor feeding season in the arctic in the summer and fall of 2018, Weller said.
Sue Moore, a biological oceanographer with NOAA Fisheries, said scientists have seen warming conditions in the arctic.
"The arctic is changing very, very quickly," Moore said. "Whales are going to have to be able to adjust to that."
While gray whales are "good at eating a variety of things," their main diet consists of anthropods located in the ocean's sediment, Moore said. Scientists are currently researching whether the sea ice, which is currently melting away in the arctic, serves as fertilizer for the anthropod sediment beds.
Without the anthropods, the gray whales will have to switch to krill or other sources of food, but they may not get the lipid-rich feed they need to survive, Moore said.
After the whales feed in the arctic, they typically move south to Mexico before making their way back north to the United States' west coast, according to the experts. During this time in the migration pattern, scientists would expect the whales to be "under peak nutritional stress," but the emaciated and malnourished state of many of the beached gray whales have made them concerned, Weller said.
The number of stranded whales could be just a fraction of the actual death toll
Most whales, especially emaciated whales, tend to sink when they're dead, said John Calambokidis, a research biologist for Cascadia Research Collective. The 70 stranded whales so far likely represent just 10% of the actual death toll, Calambokidis said.
In addition, cases of beached whales in remote areas like Alaska are much harder to find and quantify, Calambokidis said.
Scientists expect more whales to wash up dead, too. It's still early in the season for places like Washington, Canada and Alaska, so the numbers are just partial totals so far and the "event is still very much ongoing," Calambokidis said.
The population is capable of rebounding
The number of beach whales announced on Friday is the most since the last unusual mortality event (UME) was declared during the 1999 to 2000 season, experts said.
During that season, a large El Nino event could have contributed to the warming waters and less food for the whales, Moore said. However, those whales were not emaciated and were in good body condition overall, she added.
At the time, researchers were unable to determine if the deaths were caused by a mix of contributors or if it was one dominant factor, Moore said.
But based on the findings from the last UME, researchers are confident that the population can recover as long as the parameters are the same, such as the environment and the availability of food, Keller said.
Researchers are closely monitoring calf production and the population level, Keller said.
How the public can help
Experts encourage the public to report any sick, stranded or dead whales they may come across.
However, Fauquier urged people not to approach the whales, because they can harm both themselves and the animal.
In addition, it is illegal to approach them, Fauquier said.
ABC News' Morgan Winsor contributed to this report.