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Gray Whale population abundance

by NOAA Fisheries 5 Apr 19:32 UTC
Gray whale breaching © NOAA Fisheries

To understand how the eastern North Paci?c 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 Paci?c 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 ?eld 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 ?eld 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.

Current population size

In 2016 we estimated the size of the eastern North Paci?c 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. However, our most recent estimate of abundance, based on counts of southbound whales during the winter of 2023/2024, showed an increase to approximately 17,400 to 21,300 whales (NOAA Technical Memorandum NMFS-SWFSC-695).Similar declines, followed by rebounding numbers, have occurred in the population in the past, including one that was associated with a previous gray whale UME that occurred in 1999 and 2000 (see graphic below). These fluctuations highlight the population's long-term resilience to environmental changes on the population's Subarctic and Arctic feeding grounds. 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 ?xed-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.


  • 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: 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: 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: 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: 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 Paci?c gray whale call and blow rates estimated from acoustic recordings, infrared camera video, and visual sightings. Scienti?c Reports 9, 12617. doi: 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.

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