Decline in whale shark size and abundance at Ningaloo Reef over the past decade: The world's largest fish is getting smaller

CJA Bradshaw, Benjamin Fitzpatrick, CC Steinberg, BW Brook, MG Meekan

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    56 Citations (Scopus)

    Abstract

    Over-exploitation of whale sharks threatens the future of these wide-ranging pelagic fish. A long-term continuous record (4436 sightings) from a large aggregation (300-500 resident individuals) of whale sharks at Ningaloo Reef, Western Australia shows that mean shark length declined linearly by nearly 2.0 m and relative abundance measured from ecotourism sightings (corrected for variation in search effort and environmental stochasticity) has fallen by approximately 40% over the last decade. This population-level result confirms previous predictions of population decline based on projection models parameterised using mark-recapture estimates of survival. The majority of these changes are driven by reductions in the number of large individuals in the population. Phenomenological time series models support a deterministic (extrinsic) decline in large females, although there was some evidence for density dependence in large males. These reductions have occurred despite the total protection of whale sharks in Australian waters. As this species is highly migratory, the rapid change in population composition over a decade (
    Original languageEnglish
    Pages (from-to)1894-1905
    JournalBiological Conservation
    Volume141
    Issue number7
    DOIs
    Publication statusPublished - 2008

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