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ESR 4:247-256 (2008)  -  DOI:

Geographic variation in killer whale attacks on humpback whales in the North Pacific: implications for predation pressure

Gretchen H. Steiger1,*, John Calambokidis1, Janice M. Straley2, Louis M. Herman3, Salvatore Cerchio4,17, Dan R. Salden5, Jorge Urbán-R.6, Jeff K. Jacobsen7, Olga von Ziegesar8,18, Kenneth C. Balcomb9, Christine M. Gabriele10, Marilyn E. Dahlheim11, Senzo Uchida12, John K. B. Ford13, Paloma Ladrón de Guevara-P.14,19, Manami Yamaguchi15, Jay Barlow16

1Cascadia Research Collective, 2181Ú2 West Fourth Avenue, Olympia, Washington 98501, USA
2University of Alaska Southeast, 1332 Seward Avenue, Sitka, Alaska 99835, USA
3Kewalo Basin Marine Mammal Laboratory, University of Hawaii and the Dolphin Institute, 420 Ward Avenue, Honolulu, Hawaii 96814, USA
4Moss Landing Marine Laboratories, PO Box 450, Moss Landing, California 95039, USA
5Hawaii Whale Research Foundation, 52 Cheshire Drive, Maryville, Illinois 62026, USA
6Departamento de Biología Marina, Universidad Autónoma de Baja California Sur, Ap. Post 19-B, La Paz, BCS 23081, Mexico
7Humboldt State University, Department of Biological Sciences, Arcata, California 95521, USA
8North Gulf Oceanic Society, PO Box 15244, Homer, Alaska 99603, USA
9Center for Whale Research, 1359 Smuggler’s Cove Road, Friday Harbor, Washington 98250, USA
10Glacier Bay National Park, PO Box 140, Gustavus, Alaska 99826, USA
11National Marine Mammal Laboratory, NOAA, 7600 Sand Point Way NE, Seattle, Washington 98115, USA
12Okinawa Churaumi Aquarium, Motobu-cho, Okinawa-ken 905-0206, Japan
13Pacific Biological Station, Nanaimo, British Columbia V9T 6N7, Canada
14Facultad de Ciencias, Universidad Nacional Autónoma de México, Ap. Post 70-572, México DF 04510, Mexico
15Ogasawara Marine Center, Byobudani, Chichijima, Ogasawara-mura, Tokyo 100-2101, Japan
16Southwest Fisheries Science Center, 8604 La Jolla Shores Dr., La Jolla, California 92037, USA
17Present address: Wildlife Conservation Society, American Museum of Natural History, Central Park West, New York, New York 10024, USA
18Present address: Eye of the Whale, PO Box 15191, Homer, Alaska 99603, USA
19Present address: Instituto Nacional de Ecología c/o CICESE Km 107 Carr. Tijuana-Ensenada, Ensenada, BC 22860, Mexico

ABSTRACT: We examined the incidence of rake mark scars from killer whales Orcinus orca on the flukes of humpback whales Megaptera novaeangliae throughout the North Pacific to assess geographic variation in predation pressure. We used 3650 identification photographs from 16 wintering or feeding areas collected during 1990 to 1993 to determine conservative estimates in the percentage of whales with rake mark scarring. Dramatic differences were seen in the incidence of rake marks among regions, with highest rates on wintering grounds off Mexico (26 vs. 14% at others) and feeding areas off California (20 vs. 6% at others), 2 areas between which humpback whales migrate. Although attacks are rarely witnessed, the prevalence of scars demonstrates that a substantial portion of animals are attacked, particularly those that migrate between California and Mexico. Our data also suggest that most attacks occur at or near the wintering grounds in the eastern North Pacific. The prevalence of attacks indicates that killer whale predation has the potential to be a major cause of mortality and a driving force in migratory behavior; however, the location of the attacks is inconsistent with the hypothesis that animals migrate to tropical waters to avoid predation. Our conclusion is that, at least in recent decades, attacks are made primarily on calves at the wintering grounds; this contradicts the hypothesis that killer whales historically preyed heavily on large whales in high-latitude feeding areas in the North Pacific.

KEY WORDS: Killer whale · Predation · Humpback whale · Rake marks · Fluke scarring · North Pacific

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Cite this article as: Steiger GH, Calambokidis J, Straley JM, Herman LM and others (2008) Geographic variation in killer whale attacks on humpback whales in the North Pacific: implications for predation pressure. Endang Species Res 4:247-256.

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