Photo-identification of whale sharkes (Rhincodon typus) at Ningaloo Reef, Western Australia

  • Michelle Press

    Student thesis: Coursework Masters - CDU

    Abstract

    Photo-identification is a non-invasive and accurate tool that is commonly used to identify individuals within a given population. This method can assist in collecting fundamental information such as population size, dynamics and migration patterns. My study examined the applicability of this technique for biological studies of whale sharks (Rhincodon typus). Three independent photographic databases of whale sharks at Ningaloo Reef, Western Australia recorded between 1992-1996, 2002 and 2004 were analysed to determine if photo-identification techniques could be applied to these animals. Ratings of photographic quality and various methods to identify spot patterns and distinctive characteristics on each whale shark were compared and are discussed. A combination of spot and stripe patterns above behind the last gill slit and forward of the dorsal fin and distinctive scars and marks on the dorsal, caudal and pectoral fins were found to be useful for identifying individual whale sharks. These patterns appeared to be unique to individuals and distinctive markings could be recognized on some sharks for more than a decade. From 528 photographs, 276 individuals were identified. Of these, 69% were male, 14% were female and 17% were of indeterminate gender. This sex ratio did not vary among years or among months within the 2004 season of sampling. Photographed sharks ranged in size from 3-11m total length (TL). The size distribution of sharks was bimodal with a large peak at 5m and a smaller peak at 7-8m TL. A total of61 individuals (2 2%) were resighted during the study. Of these, 3 5 were resighted at different times during the same year (sometimes on multiple occasions) up to 4 months after they were initially photographed and 2 5 were resighted in different years. The interval between resightings in different years was typically 1-3 yrs, however one individual was resighted after a period of 10 yrs and 2 were resighted after a period of 12 yrs.
    Date of AwardNov 2004
    Original languageEnglish
    SupervisorMark Meekan (Supervisor)

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