Simple Modeling to Inform Harvest Strategy Policy for a Data-Moderate Crab Fishery

Mark A. Grubert, Carl J. Walters, Rik C. Buckworth, Shane S. Penny

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    Abstract

    Attempts to model the giant mud crab Scylla serrata fishery in the Northern Territory (Australia), have often been complex and the results difficult to interpret, leading to divergent estimates of fishing mortality. This has hindered the development of meaningful management policy. Additionally, analyses based on the entire Northern Territory fishery have masked the extreme variation in catches observed along the Gulf of Carpentaria coast. We applied a structurally simple model to visualize the historical patterns in stock size, recruitment, fishing mortality, and fishing mortality at maximum sustainable yield in the western Gulf of Carpentaria mud crab fishery (WGOCMCF) from 1983 to 2017. We also projected future catch and female spawning stock biomass (FSSB) under positive, neutral, and negative recruitment scenarios for three closure periods contained in the fishery harvest strategy (which start in October, if triggered) and compared these with the results of equivalent closures beginning in September. This exercise was undertaken because of known and significant changes in the proportion of fishing effort across different months as well as large variations in the proportion of females harvested each month (with both factors being particularly low in December). These differences were annualized and incorporated into the yearly time step of the model. Predicted catch and FSSB were similar for shorter closure periods (3 or 6 weeks), irrespective of the starting month. However, initiating a 3-month closure in September rather than October could lead to a 16–17% increase in FSSB under negative and average recruitment anomalies, imposing a 9–10% reduction in predicted catch. Based on our experience applying a simple model to the WGOCMCF, we also describe processes and practices that could improve the quality of assessment data for this and other data-moderate crab fisheries.

    Original languageEnglish
    Pages (from-to)125-138
    Number of pages14
    JournalMarine and Coastal Fisheries
    Volume11
    Issue number2
    Early online date11 Mar 2019
    DOIs
    Publication statusPublished - 1 Apr 2019

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    crab fishery
    crab fisheries
    fishing mortality
    mud
    spawning
    Northern Territory
    fishery
    fisheries
    modeling
    biomass
    Scylla serrata
    maximum sustainable yield
    fishing effort
    crab
    crabs
    exercise
    anomaly
    coasts
    harvest
    policy

    Cite this

    Grubert, Mark A. ; Walters, Carl J. ; Buckworth, Rik C. ; Penny, Shane S. / Simple Modeling to Inform Harvest Strategy Policy for a Data-Moderate Crab Fishery. In: Marine and Coastal Fisheries. 2019 ; Vol. 11, No. 2. pp. 125-138.
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    abstract = "Attempts to model the giant mud crab Scylla serrata fishery in the Northern Territory (Australia), have often been complex and the results difficult to interpret, leading to divergent estimates of fishing mortality. This has hindered the development of meaningful management policy. Additionally, analyses based on the entire Northern Territory fishery have masked the extreme variation in catches observed along the Gulf of Carpentaria coast. We applied a structurally simple model to visualize the historical patterns in stock size, recruitment, fishing mortality, and fishing mortality at maximum sustainable yield in the western Gulf of Carpentaria mud crab fishery (WGOCMCF) from 1983 to 2017. We also projected future catch and female spawning stock biomass (FSSB) under positive, neutral, and negative recruitment scenarios for three closure periods contained in the fishery harvest strategy (which start in October, if triggered) and compared these with the results of equivalent closures beginning in September. This exercise was undertaken because of known and significant changes in the proportion of fishing effort across different months as well as large variations in the proportion of females harvested each month (with both factors being particularly low in December). These differences were annualized and incorporated into the yearly time step of the model. Predicted catch and FSSB were similar for shorter closure periods (3 or 6 weeks), irrespective of the starting month. However, initiating a 3-month closure in September rather than October could lead to a 16–17{\%} increase in FSSB under negative and average recruitment anomalies, imposing a 9–10{\%} reduction in predicted catch. Based on our experience applying a simple model to the WGOCMCF, we also describe processes and practices that could improve the quality of assessment data for this and other data-moderate crab fisheries.",
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    Simple Modeling to Inform Harvest Strategy Policy for a Data-Moderate Crab Fishery. / Grubert, Mark A.; Walters, Carl J.; Buckworth, Rik C.; Penny, Shane S.

    In: Marine and Coastal Fisheries, Vol. 11, No. 2, 01.04.2019, p. 125-138.

    Research output: Contribution to journalArticleResearchpeer-review

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