By NOAA FISHERIES
Almost twice as many gray whale calves swam north with their mothers to their Arctic feeding grounds this spring compared to last year, according to a new count by NOAA Fisheries’ Southwest Fisheries Science Center.
The results suggest that the eastern North Pacific population of gray whales that migrate along the West Coast may be stabilizing after several years of declines. NOAA Fisheries declared an “unusual mortality event” in 2019 due to an increase in strandings that nearly cut their numbers in half.
The increase in the estimated number of calves migrating north adds to other positive signs for the population, National Oceanic and Atmospheric Administration scientists said in a news release.
“We have also seen higher numbers of mother-calf pairs in Mexican wintering lagoons and fewer whales stranding and dying on their migration north,” said Aimée Lang, who led the spring calf count. “This is a positive data point, but it is only a small improvement that we need to keep monitoring.”
Gray whales undertake one of the longest migrations of any species.
Researchers at Piedras Blancas on the central California coast estimated that 412 female gray whales swam north with calves this year. That is nearly twice the estimated all-time low of 217 mother-calf pairs migrating north last year, NOAA said, which was the fewest since surveys began in 1994.
However, it remains far below the estimate of roughly 1,500 gray whale calves in 2016, when the gray whale population contained nearly 27,000 whales. A count last winter estimated that the total population had fallen to about 14,500 whales.
Researchers from the Southwest Fisheries Science Center typically count gray whales during their southbound migration on a cycle of two out of every five years. However, they have completed three counts in the past four years and will complete another count in the winter of 2024 to track the gray whale population trajectory.
A team of NOAA researchers investigating the whales’ deaths will determine whether the increased calf estimate and recent positive signs from Mexico warrant closing the agency’s investigation into the “unusual mortality event.”
The encouraging signs in Mexico included improved body condition of gray whales in the lagoons in Baja California; more mothers with calves in the lagoons this year than any of the last five years; fewer whales died and stranded in Mexico this year than in any year since the unusual die-off started in 2019; and fewer gray whales stranded along the West Coast during their northward migration this year than during the peak years of the 2016-22 die-off.
A previous mortality event depressed gray whale numbers and calf counts in 1999 and 2000, but the population rebounded in the following years.
The current event has lasted several years longer, with a larger decline in population size. As outlined by the Marine Mammal Protection Act, investigations into mortality events continue until the resulting investigation determines that its causes have been resolved or become persistent.
As outlined by the Marine Mammal Protection Act, investigations into mortality events continue until the resulting investigation determines that its causes have been resolved or become persistent.
Strandings still a concern
But NOAA scientists said continued strandings along the Washington coast included emaciated whales that suggest some were not finding sufficient food during their summer feeding seasons in the Arctic. The whales build fat reserves in the summer to sustain their winter migration south to Mexico and then back to the Arctic again.
John Calambokidis of Cascadia Research Collective in Washington noted that 13 gray whales have stranded in that state so far this year, approaching the 15 that stranded in 2022.
This number is significantly lower than strandings in Washington in 2019 when 34 whales stranded, although higher than historic baselines.
“I think there are still some important mysteries going on here and the role of conditions in the Arctic is one,” said Calambokidis, who is part of a team of scientists probing the causes of the whales’ deaths.
The science team is analyzing stranding data and necropsy results to identify factors contributing to the deaths, such as changes in the availability of food in the Arctic, said Deborah Fauquier, the NOAA veterinary medical officer who coordinates the agency’s response to the whales’ deaths. The team has so far identified several likely contributing factors including:
- Ecosystem changes in Arctic feeding areas that may contribute to malnutrition;
- Vessel strikes and entanglements with fishing gear; and
- Predation by killer whales.
The team will determine whether the increased calf estimate and recent positive signs from Mexico warrant closing the agency’s investigation into the “unusual mortality event.”
A previous mortality event depressed gray whale numbers and calf counts in 1999 and 2000, but the population rebounded in the following years. The current event has lasted several years longer, with a larger decline in population size.