Evaluating killer whale predation on eastern North Pacific gray whales

Predation by killer whales on gray whales has been recognized for some time: for example, Rice and Wolman (1971) noted that 18% of gray whales examined at a California whaling station showed evidence of being attacked by killer whales. The importance of this predation to gray whales has not been fully evaluated, but there is increasing evidence that predation may be a significant mortality factor. Preliminary estimates have suggested that predation by mammal-eating “transient” killer whales may be responsible for mortalities constituting up to 35% of the average annual calf production of California Gray Whales (Barrett-Lennard et al. 2005), but there is substantial uncertainty about assumptions underpinning this estimate. Nonetheless, it is clear that if the “transient” killer whale population continues to increase in the eastern Pacific (Ford et al. 2007), the potential for impact on gray whales will also increase.

Killer whale attacking gray whale

A killer whale rams a young gray whale near Unimak Pass, Alaska. Photo by John Durban, working with the NOAA Alaska Fisheries Science Center and the North Gulf Oceanic Society.

Satellite tag on killer whale dorsal fin

A small (40g) satellite tag deployed on the dorsal fin of a killer whale near the Antarctic Peninsula. Photo by John Durban, Marine Mammal and Turtle Division, NOAA Southwest Fisheries Science Center.

SWFSC scientist John Durban is featured in the BBC series "Ocean Giants" as seen here The previous link is a link to Non-Federal government web site. Click to review NOAA Fisheries Disclaimeron the BBC One website. The video clip demonstrates killer whale tagging operations as part of an ongoing study to understand killer whale predation on gray whales.

To better assess the extent and importance of predation by killer whales, we are using small (40g) satellite tags (Andrews et al. 2008; Photo 2) to track the movements of killer whales relative to gray whales, and to relocate killer whales for focal follows that allow more observations of predation. Specifically, we are using this approach to study killer whales and gray whales near Monterey Bay, California, and are working with colleagues to continue research around Unimak Island, Alaska, both sites where killer whales can be regularly encountered when they prey on the young of migrating gray whales. An initial field effort took place in April 2010 in Monterey Bay and this collaboration between scientists from MMTD, the Center for Whale Research (www.whaleresearch.com)The previous link is a link to Non-Federal government web site. Click to review NOAA Fisheries Disclaimerand filmmakers from the BBC Natural history unit collected high-resolution movement data from tags on two groups of killer whales . Continued data collection in future years will further develop our assessment of the impact of killer whale predation on gray whale population dynamics.


FIGURE 1: Movements of two groups of transient killer whales (labeled CA20 and CA122) tagged in Monterey Bay, CA in April 2010. Pod CA122 (shown in red) traveled the coastline between the Columbia River in the north and the Channel Islands in the south - a linear distance of more than 1300 km, and this range was covered twice in one month. Pod CA20 (shown in blue) covered a shorter range more frequently.


Andrews, R.D., R.L. Pitman and L.T. Ballance. 2008. Satellite tracking reveals distinct movement patterns for Type B and Type C killer whales in the southern Ross Sea, Antarctica. Polar Biology 31:1461-1468.

Barrett-Lennard, L.G., C.O. Matkin, D.K. Ellifrit, J. Durban, and L. Mazzuca. 2005. Black and white versus gray: estimating kill rates, consumption rates, and population-level impacts of transient killer whales feeding on gray whales. Abstract presented to the 16th Biennial Conference on the Biology of Marine Mammals, 12–16 December 2005, San Diego, CA.

Durban, J., et al. 2010. Photographic mark-recapture analysis of clustered mammal-eating killer whales around the Aleutian Islands and Gulf of Alaska. Marine Biology. DOI 10.1007/s00227-010-1432-6

Ford, J.K.B., G.M. Ellis, and J.W. Durban. 2007. An Assessment of the Potential for Recovery of West Coast Transient Killer whales Using Coastal Waters of British Columbia. DFO Can. Sci. Advis. Sec. Res. Doc. 2007/088. http://www.dfo-mpo.gc.ca/csas/Csas/ Publications/ResDocs-DocRech/2007/2007_088_e.htm.

Laake, J., A. Punt, R. Hobbs, M. Ferguson, D. Rugh, and J. Breiwick. 2009. Re-analysis of gray whale southbound migration surveys,1967-2006. U.S. Department of Commerce, NOAA Tech. Memo. NMFS-AFSC203,55p.

Rice, D.W., and Wolman, A.A, 1971. The life history and ecology of the gray whale (Eschrichtius robustus). Special Publication of the American Society of Mammalogy, 3:viii + 1-142