Fine-scale movements of the swordfish Xiphias gladius in the Southern California Bight

Authors

  • CHUGEY A. SEPULVEDA,

    Corresponding author
    1. Pfleger Institute of Environmental Research, Oceanside, CA 92054, USA
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  • ASHLEY KNIGHT,

    1. Pfleger Institute of Environmental Research, Oceanside, CA 92054, USA
    2. Institute for Applied Marine Technology, California State University, Monterey Bay, Monterey, CA 93955, USA
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  • NICOLE NASBY-LUCAS,

    1. Pfleger Institute of Environmental Research, Oceanside, CA 92054, USA
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    • Present address: Marine Conservation Science Institute, Fallbrook, CA 92028, USA.

  • MICHAEL L. DOMEIER

    1. Pfleger Institute of Environmental Research, Oceanside, CA 92054, USA
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    • Present address: Marine Conservation Science Institute, Fallbrook, CA 92028, USA.


e-mail: chugey@pier.org

Abstract

This study reports on the fine-scale movements of swordfish (Xiphias gladius) outfitted with pop-off satellite archival transmitters (PSATs) in the Southern California Bight (SCB). PSATs were deployed on basking swordfish using traditional harpoon methods from 2004 to 2006. Transmitters were programmed for short-term deployment (2–90 days) and re-acquired using a signal direction finder. High-resolution (min−1) depth and temperature data from nine swordfish (approximately 45–120 kg) were collected (>193 days). All swordfish displayed diurnal vertical movements similar to those reported for other geographic locations. The dominant diurnal movement pattern entailed swordfish remaining below the thermocline (>68 ± 15 m) during the day and near the surface, within the upper-mixed layer, at night. Collectively, the average daytime depth (±SE) was 273 ± 11 m and the average night depth 31 ± 5 m. Three distinct vertical behaviors were recorded: 35% of the records following a strict diurnal pattern, with the entire day below the thermocline and the entire night near the surface; 52% of the records revealed routine surface-basking events during the day, with an otherwise similar distribution at night; and 13% of the records exhibited surface-oriented activity during the day and night. Surface basking (<3 m during the day) was recorded for eight individuals and occurred on 131 of the 193 days (68% of the dataset). Collectively, surface basking accounted for 8% of the total daytime records. The relevance of these vertical behaviors to SCB fisheries is discussed.

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