Changes in size distributions of commercially exploited sharks over 25 years in northern Australia using a Bayesian approach

Iain Field, R BUCKWORTH, Guo-Jing Yang, Mark Meekan, Grant Johnson, John D Stevens, Richard D Pillans, Clive McMahon, Corey Bradshaw

    Research output: Contribution to journalArticleResearchpeer-review

    Abstract

    Long-term vital rate and life-history data essential for sustainable harvest management are rare in tropical fisheries. Two commercially important shark species, Australian blacktip (Carcharhinus tilstoni) and spot-tail (C. sorrah) sharks in northern Australia have changed in size and population status over the last 25 years. These populations were exploited heavily from the early 1970s to the mid-1980s by foreign fishers, and since then have been harvested by a relatively small domestic fishery. We examined the differences in fork length of these species caught in 1983-1985 and 2002-2006 using Bayesian forms of generalised linear and mixed-effects models. We found clear regional differences and changes in size over time. For blacktips, sharks from the Gulf of Carpentaria have become smaller, and those from the western Northern Territory, larger over time. For spot-tail sharks, average size increased from the 1980s in the Gulf of Carpentaria, but not in the western Northern Territory. On average, sharks from the Gulf of Carpentaria were larger than those on the west coast of the Northern Territory, and females were larger than males. We suggest that changes over time and between regions in the size of spot-tail sharks are most likely due to over-exploitation in the past and subsequent recovery of populations. We discuss the uncertainty in trends for blacktip sharks in relation to fishing effort, availability of resources and species identification errors.
    Original languageEnglish
    Pages (from-to)262-271
    Number of pages10
    JournalFisheries Research
    Volume125-126
    DOIs
    Publication statusPublished - Aug 2012

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    shark
    sharks
    Northern Territory
    Carcharhinus limbatus
    tail
    fisheries
    Carcharhinus
    fishery
    fishing effort
    uncertainty
    life history
    coasts
    Gulf of Carpentaria
    coast
    resource
    gulf

    Cite this

    Field, I., BUCKWORTH, R., Yang, G-J., Meekan, M., Johnson, G., Stevens, J. D., ... Bradshaw, C. (2012). Changes in size distributions of commercially exploited sharks over 25 years in northern Australia using a Bayesian approach. Fisheries Research, 125-126, 262-271. https://doi.org/10.1016/j.fishres.2012.03.005
    Field, Iain ; BUCKWORTH, R ; Yang, Guo-Jing ; Meekan, Mark ; Johnson, Grant ; Stevens, John D ; Pillans, Richard D ; McMahon, Clive ; Bradshaw, Corey. / Changes in size distributions of commercially exploited sharks over 25 years in northern Australia using a Bayesian approach. In: Fisheries Research. 2012 ; Vol. 125-126. pp. 262-271.
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    abstract = "Long-term vital rate and life-history data essential for sustainable harvest management are rare in tropical fisheries. Two commercially important shark species, Australian blacktip (Carcharhinus tilstoni) and spot-tail (C. sorrah) sharks in northern Australia have changed in size and population status over the last 25 years. These populations were exploited heavily from the early 1970s to the mid-1980s by foreign fishers, and since then have been harvested by a relatively small domestic fishery. We examined the differences in fork length of these species caught in 1983-1985 and 2002-2006 using Bayesian forms of generalised linear and mixed-effects models. We found clear regional differences and changes in size over time. For blacktips, sharks from the Gulf of Carpentaria have become smaller, and those from the western Northern Territory, larger over time. For spot-tail sharks, average size increased from the 1980s in the Gulf of Carpentaria, but not in the western Northern Territory. On average, sharks from the Gulf of Carpentaria were larger than those on the west coast of the Northern Territory, and females were larger than males. We suggest that changes over time and between regions in the size of spot-tail sharks are most likely due to over-exploitation in the past and subsequent recovery of populations. We discuss the uncertainty in trends for blacktip sharks in relation to fishing effort, availability of resources and species identification errors.",
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    Field, I, BUCKWORTH, R, Yang, G-J, Meekan, M, Johnson, G, Stevens, JD, Pillans, RD, McMahon, C & Bradshaw, C 2012, 'Changes in size distributions of commercially exploited sharks over 25 years in northern Australia using a Bayesian approach', Fisheries Research, vol. 125-126, pp. 262-271. https://doi.org/10.1016/j.fishres.2012.03.005

    Changes in size distributions of commercially exploited sharks over 25 years in northern Australia using a Bayesian approach. / Field, Iain; BUCKWORTH, R; Yang, Guo-Jing; Meekan, Mark; Johnson, Grant; Stevens, John D; Pillans, Richard D; McMahon, Clive; Bradshaw, Corey.

    In: Fisheries Research, Vol. 125-126, 08.2012, p. 262-271.

    Research output: Contribution to journalArticleResearchpeer-review

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