Gray Whale Population Abundance
To understand how the eastern North Pacific gray whale population is responding to changes in the environment following its recovery from low numbers due to commercial whaling, we study changes in abundance over time.
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What We Do
Monitoring gray whale population abundance is one of the primary focus areas for gray whale research at NOAA Fisheries. We estimate the abundance (i.e., the number of whales) of the eastern North Pacific gray whale population by conducting shore-based surveys overlapping with the timing of the southward migration from the Arctic to Mexico. Surveys of this type began in 1967 and take place at our Granite Canyon field station south of Monterey, California.
We combine new and established methods to count southbound gray whales passing Granite Canyon from December through February, including:
Visual Surveys
Often the simplest marine mammal survey method is also one of the best. Taking three-hour shifts, visual observers watch through binoculars for the telltale “blows” of gray whales. After spotting whales and recording their coordinates, the observers are then able to count and track the whales as they migrate south using a custom-built computer program.
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Infrared Cameras
We use infrared video cameras to count and track whales at Granite Canyon. These cameras look out over the ocean, recording the view in terms of temperature. The warm breath of a gray whale exhalation stands out against the cold ocean surface. This thermal contrast is distinctive enough that computers can scan the video and count the exhalations automatically. These cameras can detect whales passing at night when visual observers cannot.
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Fixed-wing Drones
We are also using a small fixed-wing drone or uncrewed aerial system to conduct photographic surveys of gray whales migrating past the Granite Canyon field station. These aircraft collect very high-resolution images that can be used to refine visual estimates of gray whale group sizes and estimate how many whales pass through the study area without being detected. In the future, these small remotely piloted aircraft may provide a safe and cost-effective alternative to crewed aerial surveys measuring the distribution and density of gray whales and other marine wildlife species.
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Population Size
In 2016 we estimated the size of the eastern North Pacific gray whale population to be between 25,000 to 30,000 animals, which was one of the highest estimates of our data time series that extends back to 1967. Starting in December 2018, however, the number of dead gray whales stranding along the west coast increased, leading to the declaration of an Unusual Mortality Event (UME) for eastern North Pacific gray whales that lasted through November 2023. This event was associated with ecosystem changes in Arctic and sub-Arctic feeding areas that reduced the availability of the whales’ food supply. As a result, many whales showed signs of malnutrition, fewer calves were born, and mortality increased. The impact of this UME could be seen during our next three surveys. By the winter or 2022/2023, we estimated that there were approximately 13,300 to 16,000 whales in the population, which was roughly comparable to the number of gray whales when counts first began in the late 1960s.
Declines in estimated abundance that have occurred in the past, including one that was associated with a previous gray whale UME in 1999 and 2000, have generally been followed by periods of increasing numbers (see graphic below). Since the UME was closed in 2023, however, estimates of abundance have fluctuated, reaching a low of approximately 11,700 to 14,200 whales in 2024/2025 before an apparent increase to between 15,930 and 20,530 whales in 2025/2026. The apparent increases observed in some recent years exceed expected growth rates for baleen whales and have occurred during periods of low calf production, indicating that factors other than demographic events (i.e., births and deaths) must be affecting the estimated abundance of whales passing the central California coast. Several factors may be contributing to these changes. For example, gray whales may be changing their migration patterns, making different numbers of whales available to be counted each year. Factors intrinsic to the survey and analysis (e.g., sampling error, analytical bias, changes in detection probabilities) may also be influencing the estimates. We plan to address some of these possibilities through targeted studies in coming years and the development of new analytical approaches.
Although the recent apparent increase in abundance is encouraging, the low calf production that has occurred since 2019 raises concerns that recent and continued environmental changes in the Arctic and sub-Arctic feeding grounds could be impacting population resilience. We will continue to closely monitor the population’s response to the most recent UME with regular surveys to estimate abundance, calf production, and body condition.
New Technology: Drones
In 2020 we began testing the feasibility of using fixed-wing drones (or uncrewed aerial systems) to enhance our ability to count migrating gray whales. During the winter migration, we launched a small autonomous drone from Granite Canyon. The drone flies a pre-programmed pattern, continuously collecting photographs over a roughly 700-meter-wide swath of ocean surface. Artificial intelligence is being developed to efficiently detect whales in the hundreds of images typically collected during a single drone flight. These systems can be used to sample large areas, flying up to 34 mph. NOAA’s Uncrewed Systems Research to Transitions Office supports this research.
Potential applications for this new technology include:
- Estimating densities of whales in sensitive areas such as shipping lanes and in proximity to marine energy development areas.
- Matching estimates of the number of passing whales with measurements of fishing gear to assess the risk of entanglement.
- Evaluating the proportion of whales that may be missed by the visual observers on shore.
About Our Team
This project is directed by Dr. David Weller and led by research wildlife biologists Dr. Tomo Eguchi, Dr. Trevor Joyce, and Dr. Aimée Lang. These scientists also work closely with the International Whaling Commission and the International Union for Conservation of Nature (IUCN) on the conservation of whale populations Pacific-wide.
Publications
Lang, Aimée, Tomo Eguchi, and David Weller. 2026. Abundance of eastern North Pacific Gray Whales 2025/2026. U.S. Department of Commerce, NOAA Technical Memorandum NMFS-SWFSC-737. doi: 10.25923/yk4w-dd52.
Eguchi, Tomo, Aimée Lang, and David Weller. 2025. Abundance of eastern North Pacific gray whales 2024/2025. U.S. Department of Commerce, NOAA Technical Memorandum NMFS-SWFSC-724. doi: 10.25923/jqea-s505
Eguchi, Tomo, Aimée Lang, and David Weller. 2024. Abundance of eastern North Pacific gray whales 2023/2024. U.S. Department of Commerce, NOAA Technical Memorandum NMFS-SWFSC-695. doi: 10.25923/n5qa-0y54
Joshua D. Stewart, Joyce, T.W., Durban, J.W., Calambokidis, J., Fauquier, D., Fearnbach, D., Grebmeier, J.M., Lynn, M., Manizza, M., Perryman, W.L., Tinker, M.T., & Weller, D.W., 2023. Boom-bust cycles in gray whales associated with dynamic and changing Arctic conditions. Science 382, 207-211.doi: 10.1126/science.adi1847.
Eguchi, Tomoharu, Aimée R. Lang & David W. Weller. 2023. Abundance of eastern North Pacific gray whales 2022/2023. U.S. Department of Commerce, NOAA Technical Memorandum NMFS-SWFSC-680.
Joshua D. Stewart, Joyce, T.W., Durban, J.W., Calambokidis, J., Fauquier, D., Fearnbach, D., Grebmeier, J.M., Lynn, M., Manizza, M., Perryman, W.L., Tinker, M.T., & Weller, D.W., 2023. Boom-bust cycles in gray whales associated with dynamic and changing Arctic conditions. Science 382, 207-211.doi: 10.1126/science.adi1847.
Eguchi, T., Lang, A. R., & Weller, D. W. 2022. Abundance and migratory phenology of eastern North Pacific gray whales 2021/2022. U. S. Department of Commerce, NOAA Technical Memorandum NMFS-SWFSC-668.
Stewart, J. D., & Weller, D. W. 2021. Abundance of eastern North Pacific gray whales 2019/2020. U.S. Department of Commerce, NOAA Technical Memorandum NMFS-SWFSC-639.
Perryman, W.L., Joyce, T., Weller, D.W., & Durban, J.W. 2021. Environmental factors influencing eastern North Pacific gray whale calf production 1994–2016. Marine Mammal Science 37:448-62.
Sullivan, K., Fennell, M., Perryman, W., & Weller, D. 2020. Automated detection, tracking, and counting of gray whales. Proc. SPIE 11409. Thermosense: Thermal Infrared Applications XLII, 1140906 (23 April 2020). doi: 10.1117/12.2567187.
Guazzo, R.A., Weller, D.W., Europe, H.M., Durban, J. W., D’Spain, G. L., & Hildebrand, J. A. 2019. Migrating eastern North Pacific gray whale call and blow rates estimated from acoustic recordings, infrared camera video, and visual sightings. Scientific Reports 9, 12617. doi: 10.1038/s41598-019-49115-y.
Durban, J.W., D.W. Weller, A.R. Lang, & W.L. Perryman. 2015. Estimating gray whale abundance from shore-based counts using a multilevel Bayesian model. Journal of Cetacean Research and Management 15:61-68.
Laake, J.L., Punt, A.E., Hobbs, R., Ferguson, M., Rugh, D., & Breiwick, J. 2012. Gray whale southbound migration surveys 1967-2006: An integrated re-analysis. Journal of Cetacean Research and Management 12:287-306.