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.
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.
- 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.
- 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.
Population Size
In 2016 we estimated the size of the eastern North Pacific gray whale population to be nearly 27,000, 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 localized ecosystem changes in the whale's Subarctic and Arctic feeding areas that led to changes in food, malnutrition, decreased birth rates, and increased mortality. The impact of this UME could be seen during our next three surveys, as the population declined to approximately 13,230 - 15,960 whales in the winter 2022/2023, which was roughly comparable to the number of gray whales when counts first began in the late 1960s. While the 2023/2024 estimate of abundance of ENP gray whales showed an apparent increase, the estimate for 2024/2025, which was between 11,700 and 14,450 whales, was the third lowest in the time series (NOAA Technical Memorandum NMFS-SWFSC-724). 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). However, the duration and magnitude of the current decline, coupled with the low calf production that has occurred since 2019, raise 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
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
Eguchi, Tomo, Aimée R. Lang, and David W. 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.