Population Abundance Research
Gray whale research in the news
The eastern North Pacific gray whale (also known as the California Gray Whale) population has been hunted extensively by both commercial and aboriginal whalers, with intense commercial takes in the late 19th and early 20th centuries greatly reducing the population from an estimated pre-exploitation size of between 15,000 and 24,000 animals. Commercial whaling ended in 1946, and gray whales were listed as endangered under the U.S. Endangered Species Act in 1973. Since this time the California Gray Whale is believed to have remained close to the carrying capacity of the ecosystem for these animals. Specifically, the most recent population estimate from abundance counts in 2006/2007 was approximately 19,000 whales, with a high probability (88%) that the population is at “optimum sustainable population” size, as defined by the Marine Mammal Protection Act. This indicates that the California Gray Whale population is no longer depleted.
IUCN status: The eastern North Pacific population is listed by the IUCN as “Least Concern”
The eastern North Pacific gray whale population summers and feeds mainly in the Chukchi, Beaufort and the northwestern Bering Seas. The population migrates south along the coast in the autumn to wintering grounds on the west coast of Baja California, Mexico, and the southeastern Gulf of California to breed, bear and nurse their young, and cavort before returning to the Arctic. SWFSC scientists monitor this migration each year, conducting shore-based surveys from two sites on the California coast.
Gray whales undertake one of the longest annual migrations of any mammal, traveling some 15,000-20,000 km round trip. By late November, most gray whales are moving south from summer feeding areas to winter calving areas. This southern migration is segregated by age, sex and reproductive condition. The first pulse of migrants is led by: (a) near-term pregnant females, followed by (b) estrous females and mature males and then (c) immature animals of both sexes.
Migrating gray whales move steadily in one direction, breathing and diving in predictable patterns. They commonly travel alone or in small unstable groups, although large aggregations can occur on both the feeding and breeding grounds. Except for mother-calf pairs, associations between individuals are relatively fluid.
SWFSC scientists conduct shore-based surveys for southbound gray whales from the Granite Canyon Marine Laboratory, located on the Big Sur coast about 8 miles south of Carmel, CA. The sighting data, collected in collaboration with scientists from NOAA Fisheries Service's Alaska Fisheries Science Center, are used to estimate the abundance of the eastern north Pacific gray whale. The Granite Canyon field site had been in use for this purpose since 1975. This field work has been conducted in California during December-February in 25 different years since 1967-68. Population estimates based on these data indicate that gray whales increased substantially in population size over the first three decades of monitoring.
This project, along with the SWFSC survey of northbound gray whales and analyses of ice distribution information from the Arctic, enables us to study the link between reproduction in this population and inter-annual climate variability in the Arctic where these whales feed in the summer months. This work has the potential to shed light on important questions about the impacts of climate change on Arctic ecosystems, and on gray whales and other species that depend on these ecosystems for their survival.
Figure 1: Abundance estimates of the eastern North Pacific gray whale population from 1967 to 2006
data: NOAA Alaska Fisheries Science Center
Allen, B.M. and R.P. Angliss. 2009 Alaska Marine Mammal Stock Assessments, 2009. NOAA Technical Memorandum NMFS-AFSC-206.
Calambokidis, J., J.L. Laake, and A. Klimak. 2010. Abundance and population structure of seasonal gray whales in the Pacific Northwest, 1998-2008. Paper SC/62/BRG32 presented to the IWC Scientific Committee.
Durban, J., Land, A., Weller D., Rugh, D., Hobbs, R., and Perryman, W. 2010. Comparing two methods of shore-based counts of eastern North Pacific gray whales. Paper SC/62/BRG8 presented to the IWC Scientific Committee.
Laake, J. L., A. Punt, R. Hobbs, M. Ferguson, D. Rugh, and J. Breiwick. 2009. Re-analysis of gray whale southbound migration surveys, 1967-2006, 55 p. NOAA Technical Memorandum NMFS-AFSC-203
Perryman, W., Donahue, M., Laake, J., and T. Martin. 1999. Diel variation in migration rates of eastern Pacific gray whales measured with thermal imaging sensors. Marine Mammal Science, 15(2):426-445.
Punt, A.E., and P.R. Wade. 2010. Population status of the eastern North Pacific stock of gray whales in 2009, 43 p. NOAA Technical Memorandum NMFS-AFSC-207.