Decline in whale shark size and abundance at Ningaloo Reef over the past decade

The world's largest fish is getting smaller

Corey Bradshaw, B Fitzpatrick, C Steinberg, B BROOK, Mark G Meekan

    Research output: Contribution to journalArticleResearchpeer-review

    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 (<1 whale shark generation) supports the hypothesis of unsustainable mortality in other parts of their range (e.g., overfishing), rather than the alternative of long-term abiotic or biotic shifts in the environment. As such, effective conservation of whale sharks will require international protection, and collaborative tagging studies to identify and monitor migratory pathways. Crown Copyright � 2008.
    Original languageEnglish
    Pages (from-to)1894-1905
    Number of pages12
    JournalBiological Conservation
    Volume141
    Issue number7
    Publication statusPublished - 2008

    Fingerprint

    shark
    whale
    reefs
    reef
    fish
    ecotourism
    pelagic fish
    overfishing
    sharks
    Western Australia
    density dependence
    tagging
    population decline
    stochasticity
    time series analysis
    world
    Rhincodon typus
    relative abundance
    prediction
    time series

    Cite this

    Bradshaw, C., Fitzpatrick, B., Steinberg, C., BROOK, B., & Meekan, M. G. (2008). Decline in whale shark size and abundance at Ningaloo Reef over the past decade: The world's largest fish is getting smaller. Biological Conservation, 141(7), 1894-1905.
    Bradshaw, Corey ; Fitzpatrick, B ; Steinberg, C ; BROOK, B ; Meekan, Mark G. / Decline in whale shark size and abundance at Ningaloo Reef over the past decade : The world's largest fish is getting smaller. In: Biological Conservation. 2008 ; Vol. 141, No. 7. pp. 1894-1905.
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    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 (<1 whale shark generation) supports the hypothesis of unsustainable mortality in other parts of their range (e.g., overfishing), rather than the alternative of long-term abiotic or biotic shifts in the environment. As such, effective conservation of whale sharks will require international protection, and collaborative tagging studies to identify and monitor migratory pathways. Crown Copyright � 2008.",
    keywords = "abundance, density dependence, ecotourism, mark-recapture method, migratory behavior, population decline, population size, shark, tagging, Australasia, Australia, Ningaloo Reef, Western Australia, Cetacea, Chondrichthyes, Rhincodon typus, Rhincodontidae",
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    Bradshaw, C, Fitzpatrick, B, Steinberg, C, BROOK, B & Meekan, MG 2008, 'Decline in whale shark size and abundance at Ningaloo Reef over the past decade: The world's largest fish is getting smaller', Biological Conservation, vol. 141, no. 7, pp. 1894-1905.

    Decline in whale shark size and abundance at Ningaloo Reef over the past decade : The world's largest fish is getting smaller. / Bradshaw, Corey; Fitzpatrick, B; Steinberg, C; BROOK, B; Meekan, Mark G.

    In: Biological Conservation, Vol. 141, No. 7, 2008, p. 1894-1905.

    Research output: Contribution to journalArticleResearchpeer-review

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    T2 - The world's largest fish is getting smaller

    AU - Bradshaw, Corey

    AU - Fitzpatrick, B

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    AU - BROOK, B

    AU - Meekan, Mark G

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    N2 - 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 (<1 whale shark generation) supports the hypothesis of unsustainable mortality in other parts of their range (e.g., overfishing), rather than the alternative of long-term abiotic or biotic shifts in the environment. As such, effective conservation of whale sharks will require international protection, and collaborative tagging studies to identify and monitor migratory pathways. Crown Copyright � 2008.

    AB - 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 (<1 whale shark generation) supports the hypothesis of unsustainable mortality in other parts of their range (e.g., overfishing), rather than the alternative of long-term abiotic or biotic shifts in the environment. As such, effective conservation of whale sharks will require international protection, and collaborative tagging studies to identify and monitor migratory pathways. Crown Copyright � 2008.

    KW - abundance

    KW - density dependence

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    KW - migratory behavior

    KW - population decline

    KW - population size

    KW - shark

    KW - tagging

    KW - Australasia

    KW - Australia

    KW - Ningaloo Reef

    KW - Western Australia

    KW - Cetacea

    KW - Chondrichthyes

    KW - Rhincodon typus

    KW - Rhincodontidae

    M3 - Article

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    SN - 0006-3207

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    ER -