It was a worrisome few years for North Pacific gray whales, with hundreds washing up dead on shorelines along the West Coast leading to an estimated 30% decline in their population.
But the gray whale population, which travels from Alaska where they feed to breeding grounds in Mexico, passing Southern California along the way, is now considered healthy enough the National Oceanic Atmospheric Administration this week declared closed the Unusual Mortality Event, or UME, it designated in 2019.
A Unusual Mortality Event declaration by NOAA happens when there’s a significant die off of any marine mammal population, such as the case when nearly 700 gray whales deaths were recorded off the coast from Mexico to Canada between 2019 and 2023.
“Understanding and investigating marine mammal UMEs is crucial because they can be indicators of ocean health, giving insight into larger environmental issues ,which may also have implications for human health,” NOAA officials said.
During the years of the Unusual Mortality Event, 347 gray whales were stranded along the coasts of California, Oregon and Washington; another 316 were reported in Mexico and 27 in Canada.
NOAA and a team of researchers concluded that the preliminary cause of the usually high number of deaths was “localized ecosystem changes” in the whale’s feeding areas that led to changes in their food sources, which then led to malnutrition – a common cause in many of the deaths – as well as decreased birth rates and increased mortality, NOAA’s announcement this week said.
“There was a concern that there was a shift in the food. Many were skinny or malnourished, which ties into a food issue,” said Alisa Schulman-Janiger, co-founder of the Gray Whale Census and Behavior Project based off Point Vicente in Palos Verdes. The project’s group of volunteers spend the whales’ migration season counting the passing marine mammals and noting their appearance.
Schulman-Janiger called the declaration of the Unusual Mortality Event’s closure “overall, good news.”
“But we have to keep an eye out – we have to continue monitoring,” she said.
And NOAA’s stranding network will be, said Justin Viezbicke, California stranding coordinator for NOAA’s Marine Mammal Health and Stranding Response. It will continue to respond to dead gray whales in an effort to monitor the population and learn more about the species and possible threats to its population, he said.
The population numbers of the North Pacific gray whale had a decline during the Unusual Mortality Event, going from an estimated 20,500 whales in 2019 to 14,526 whales in 2023. Updated population numbers are expected to come out soon, and Schulman-Janiger said she hopes they will show a rebound in the whales’ numbers.
Many of the strandings, especially in 2019 when there was a spike in deaths, were reproductive females, taking a lot of moms or would-be-moms out of the equation, Schulman-Janiger noted.
And the number of dead only indicates the whales that were found, not the ones that died out at sea, out of sight and not counted by researchers, she said.
Total calf production also declined, from around 950 calves counted in 2018 to an estimated 217 calves in 2022. In 2023, calf production increased slightly to 412 counted.
Schulman-Janiger and the volunteers who watch the whales from the Palos Verdes Peninsula cliffs noticed the same uptick in calves last year, as did NOAA and researchers down in lagoons off Mexico.
“What we are looking at is trends, which almost always mirrors NOAA’s counts,” she said.
Researchers will have to keep an eye out on water temperatures and climate change in the gray whales’ feeding areas and how that impacts their food sources, Schulman-Janiger said.
“We don’t believe the gray whale population will continue to decline, but the population will depend on: Can they find food, can they gain enough weight?” she said. “A lot of conditions have to come together.”