A new abundance estimate of the gray whale population that migrates along the West Coast suggests their numbers have increased since last year.
Researchers at NOAA Fisheries’ Southwest Fisheries Science Center estimate that the Eastern North Pacific gray whale population is between 15,930 to 20,530, or an average of about 17,750 gray whales. That is a jump from last year’s estimate—one of the lowest since counting began in the late 1960s—which numbered between 11,690 to 13,190, or about 12,890 whales.
The apparent increase is welcome news and similar to fluctuations seen in some previous years. Yet, it raises questions about the assumptions we have tested and used in the past to inform our analytical approaches to the population estimate. We are examining:
- The relationship between demographics and environmental variability
- Whale migratory cadence and timing
- Previous assumptions made about whale behavior used to calculate the abundance estimation
The new numbers are based on a count of whales migrating south prior to their return migration north. Many gray whales stranded along the West Coast this spring before reaching their Arctic feeding grounds near Alaska. Some of the stranded whales were skinny or emaciated, suggesting they are not finding sufficient food to sustain their round-trip migration between Alaska and Mexico.
Eastern North Pacific gray whales rebounded from lows during the commercial whaling era and were removed from the list of endangered species in 1994. Their numbers climbed to an estimated peak in 2015–2016 of between 24,890 and 29,760, or an average of about 27,000 whales. However, a spike in strandings led NOAA Fisheries to declare an unusual mortality event (UME) in 2019. The agency closed the UME in 2023 as the cause became a persistent issue and strandings began to decline.
The number of strandings in the last two years have since climbed back into the general range recorded during the UME, when many stranded whales were similarly malnourished. Since the factors driving the continued strandings remain largely the same, the strandings do not yet meet the criteria for a new UME.
Several Factors May Affect Gray Whale Numbers
Researchers note that the estimated increase in gray whale numbers since last year likely exceeds the reproductive capacity of the population. The last estimate of gray whale calves in 2025 was 85, the lowest on record. The apparent increase could reflect other factors related to the survey and analysis including the possibility that some of the tested assumptions about gray whale migratory behavior used in the analytical methods have changed.
Since scientists use models to calculate the annual estimates based on visual counts and other information, they always carry some uncertainty or margin of error. That makes them most valuable for tracking trends over time rather than focusing on pinpointing the exact number of whales at a specific date.
“We know that we don’t see every whale,” said Aimee Lang, a research scientist at the Science Center who helps lead the counts. “One of the questions raised by our most recent count is whether we see a consistent proportion of the population every year, or whether other factors affect how much of the population we see and count.”
Some whales may be testing new strategies. For instance, tens of gray whales have left their usual north-south migration route to temporarily occupy San Francisco Bay and other areas on the West Coast in recent years, possibly looking for food. Not all whales follow the same migratory and feeding strategies, but it’s not yet clear how that might affect the counts each year.
Additional research aims to refine counting methods and improve analytical methods used in estimating abundance. For example, researchers are using drones to determine how accurately counting teams estimate the size of groups of whales they observe passing by their watch station on the central California Coast.
Environmental Changes Can Affect Recovering Populations
New findings last year showed large whale populations with the strongest recoveries from the lows of the commercial whaling era may be most affected by changes in environmental conditions. Those growing populations will likely be the first to reach the capacity of the environment to sustain them. Changes in those environmental limits could affect populations such as Eastern North Pacific gray whales.
“This presents another paradox: Populations that are considered recovered or close to recovery will likely be the first to exhibit climate-associated downturns,” the scientists wrote. “Depleted populations, in contrast, are less likely to experience climate-driven declines until prey availability decreases” to the point that it limits the size of the populations.