The influence of biophysical processes on distributions of the whale shark Rhincodon typus (Smith 1828), at Ningaloo Reef, Western Australia

  • Jai Caleb Sleeman

    Student thesis: Doctor of Philosophy (PhD) - CDU


    This thesis addresses the broad questions; ‘(i) What are the spatial / temporal distributions of whale sharks, (ii) how do these compare to marine megafauna with different trophic and metabolic strategies, and (iii) how are they influenced by biophysical variables in the north east Indian Ocean?’

    Broad scale biophysical variables were compared with historical seasonal whale shark sightings at Ningaloo Reef, Western Australia using generalised linear mixedeffects modelling (GLMM). The combined variables: Southern Oscillation Index and wind shear had greatest support for explaining increased whale shark abundance during La Nińa years.

    Finer scale spatial and temporal (i.e. within reef, weekly) distribution patterns of krill feeders and other trophic groups of marine megafauna at Ningaloo Reef were determined through GIS and GLMM analysis of sightings and satellite derived biophysical variables. At local scales, relative biomass of krill feeders (i.e. whale sharks, minke whales and manta rays) were linked to bathymetry, but further investigations were required to determine how physical processes influenced their movement.

    Using an agent-based diffusion model and GLMMs, the movements of four whale sharks (tracked via satellite tags) were compared to geostrophic surface currents to determine whether sharks were passively drifting in currents or actively swimming. Results from the agent based diffusion model and GLMMs found that there was little support for passive drifting, and suggests that shark diving patterns would provide more information on associations with biophysical factors.

    Using GLMMs whale shark dive patterns were modelled to determine the influence of temperature and dissolved oxygen on their 3-dimensional profiles. Whale shark dives were linked to temperature and dissolved oxygen presumably due to physiological limitations of large aquatic poikilotherns and energetic conservation mechanisms.
    Date of AwardAug 2012
    Original languageEnglish
    SupervisorGuy Stuart Boggs (Supervisor), Mark Meekan (Supervisor) & Corey Bradshaw (Supervisor)

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