Abstract: gray whale foraging (fwd)

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Date: Wed Dec 26 2001 - 09:33:05 EST

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    From: Dave Duffus <dduffus@office.geog.uvic.ca>

    This article was recently published in Marine Ecology Progrss Series

    Marine Ecology Progress Series 223:299-310 (2001)

    Foraging patterns of gray whales in central Clayoquot
    Sound, British Columbia, Canada

    Jason S. Dunham*, David A. Duffus
    Whale Research Laboratory, Department of Geography, University of Victoria, PO
    Box 3050, Victoria, British Columbia V8W 3P5, Canada
    E-mail: jdunham@horizon.bc.ca

    ABSTRACT: Gray whales Eschrichtius robustus forage in parts of Clayoquot
    Sound on several prey species in different habitats. Between June and
    September in 1996 and 1997 we carried out analyses of the density, biomass,
    and other measures of their primary prey species, and of whales' movement
    patterns in response to prey characteristics. The prey base consists of
    hyper-benthic mysids (family Mysidae), pelagic porcelain crab larvae (4
    spp. of family Porcellanidae), benthic amphipods (family Ampeliscidae) and
    benthic ghost shrimp Callianassa californiensis. Whales foraged primarily
    for mysids, switching to porcelain crab larvae in August, and then to
    amphipods even later in the season when these organisms increased in body
    size. In 1997, whales rapidly switched from feeding on planktonic to
    benthic prey during mid-August. Sampling indicated low numbers of mysids
    and crab larvae at that time. Selection of amphipod prey was based on high
    biomass and a high proportion of individuals [greater equal]6 mm in length.
    In parts of the study area gray whales did not return to forage on benthic
    amphipods when this size criteria was not met. A single whale departed from
    a ghost shrimp feeding ground because its search time for food was long, it
    achieved only a low biomass removal rate, and it was not able to find
    sufficient food each day. We show that gray whales are dynamic and
    selective foragers that switch prey and foraging tactics rapidly to take
    advantage of short-term availability of energy.

    KEY WORDS: Gray whale, Eschrichtius robustus, Prey selection,
    Prey-switching Plankton, Benthos,Clayoquot Sound

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