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.
Current 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. Since January 2019, however, the number of dead gray whales stranding along the west coast has been elevated; this event, which continues to date, has been declared an Unusual Mortality Event (UME). The impact of this UME could be seen during our next two surveys, which estimated that the population had declined to approximately 20,500 whales in winter 2019/2020 and even further to approximately 16,650 whales in the winter of 2021/2022. Similar declines have occurred in the past, including one that was associated with a previous gray whale UME that occurred in 1999 and 2000. Following these past declines, the eastern North Pacific gray whale population has rebounded, demonstrating long-term resilience to these fluctuations. We will continue to closely monitor the population’s response to the current UME with regular surveys to estimate abundance, calf production, and body condition.
New Technology: Drones
- 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, T., Lang, A. R., and 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. https://doi.org/10.25923/x88y-8p07
Stewart, J. D. and Weller, D. W. 2021. Abundance of eastern North Pacific gray whales 2019/2020. U.S. Department of Commerce, NOAA Technical Memorandum NMFS-SWFSC-639. https://doi.org/10.25923/bmam-pe91
Perryman, W.L., Joyce, T., Weller, D.W. and Durban, J.W. 2021. Environmental factors influencing eastern North Pacific gray whale calf production 1994–2016. Marine Mammal Science 37:448-62. https://doi.org/10.1111/mms.12755
Sullivan, K., Fennell, M., Perryman, W. and 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., and 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. https://doi.org/10.1038/s41598-019-49115-y
Durban, J.W., D.W. Weller, A.R. Lang, and 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. and Breiwick, J. 2012. Gray whale southbound migration surveys 1967-2006: An integrated re-analysis. Journal of Cetacean Research and Management 12:287-306.