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Authors

Gretchen H. Steiger, Cascadia Research Collective, 218% West Fourth Avenue, Olympia, Washington 98501, USA
John Calambokidis, Cascadia Research Collective, 218% West Fourth Avenue, Olympia, Washington 98501, USAFollow
Janice M. Straley, niversity of Alaska Southeast, 1332 Seward Avenue, Sitka, Alaska 99835, USA
Louis M. Herman, ~ewalBoa sin Marine Mammal Laboratory, University of Hawaii and the Dolphin Institute, 420 Ward Avenue, Honolulu, Hawaii 96814, USA
Salvatore Cerchio, OSS Landing Marine Laboratories, PO Box 450, Moss Landing, California 95039, USA
Dan R. Salden, ~awaiiW hale Research Foundation, 52 Cheshire Drive, Maryville, Illinois 62026, USA
Jorge Urban-R., Departamento de Biologia Marina, Universidad Aut6noma de Baja California Sur, Ap. Post 19-B, La Paz, BCS 23081, Mexico
Jeff K. Jacobsen, ~umboldt State University, Department of Biological Sdences, Arcata, California 95521, USA
Olga von Ziegesar, ~ o r t hG ulf Oceanic Society, PO Box 15244, Homer, Alaska 99603, USA
Kenneth C. Balcomb, Center for Whale Research, 1359 Smuggler's Cove Road, Friday Harbor, Washington 98250, USA
Christine M. Gabriele, Glacier Bay National Park, PO Box 140, Gustavus, Alaska 99826, USA
Marilyn E. Dahlheim, ~ational Marine Mammal Laboratory, NOAA, 7600 Sand Point Way NE, Seattle, Washington 98115, USA
Senzo Uchida, Okinawa Churaumi Aquarium, Motobu-cho, Okinawa-ken 905-0206, Japan
John K. B. Ford, 3pacific Biological Station, Nanaimo, British Columbia V9T 6N7, Canada
Paloma Ladron de Guevara-P., Facultad de Ciencias, Universidad Nacional Aut6noma de Mbxico, Ap. Post 70572, MWco DF 04510, Mexico
Manami Yamaguchi, 50gasawara Marine Center, Byobudani, Chichijima, Ogasawara-mura, Tokyo 100-2101, Japan
Jay Barlow, Southwest Fisheries Science Center, 8604 La Jolla Shores Dr., La Jolla, California 92037, USA

Date of this Version

6-2008

Comments

Published in Endangered Species Research Vol. 4: 247-256, 2008.

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 geo- graphic 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.

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