Effects of Tidal and Diel Cycles on Dugong Habitat Use

Authors

  • JAMES K. SHEPPARD,

    Corresponding author
    1. School of Earth and Environmental Sciences, James Cook University, Townsville 4811, Queensland, Australia
      jsheppard@sandiegozoo.org
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    • Conservation and Research for Endangered Species, Applied Animal Ecology, Zoological Society of San Diego, 15600 San Pasqual Valley Road, Escondido, CA 92027–7000, USA

  • RHONDDA E. JONES,

    1. School of Tropical Biology, James Cook University, Townsville 4811, Queensland, Australia
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  • HELENE MARSH,

    1. School of Earth and Environmental Sciences, James Cook University, Townsville 4811, Queensland, Australia
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  • IVAN R. LAWLER

    1. School of Earth and Environmental Sciences, James Cook University, Townsville 4811, Queensland, Australia
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jsheppard@sandiegozoo.org

Abstract

ABSTRACT  Quantifying the factors influencing behaviors of aquatic mammalian grazers may enhance the generic understanding of grazer ecology. We investigated diel and tidal patterns in movements of the dugong (Dugong dugon) by Global Positioning System—tracking 12 animals in 5 inshore—intertidal and 3 offshore—subtidal habitats along the coast of Queensland, Australia. We examined effects of tide height and time of day on the dugong's distance from 1) the nearest coast, 2) water >3 m deep, 3) actual water depth (bathymetry + tide ht) experienced, and 4) distribution of the directions of movements. Both tidal and diel cycles influenced dugong movement. Tracked dugongs tended to be closer to shore at high tide than at low tide and closer to shore at night than during the day. Onshore movement was more prevalent on incoming tides and in the afternoon and evening. Offshore movement was more prevalent on outgoing tides and from midnight through the morning until midday. Tidal and diel variation in water depths used by the inshore—intertidal dugongs was small, but probably underestimated, hidden by a sampling bias in the telemetry equipment. Onshore movement at high tide allowed dugongs to exploit intertidal seagrass beds. Dugongs are closer to shore in afternoons and evenings than in mornings. This behavior may be related to the avoidance of predators or watercraft. Our findings can be used to predict spatial patterns of dugongs within areas of conservation management significance and to assess, avoid, and mitigate adverse effects of anthropogenic disturbance.

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