Gulf_Menhaden_Fisheries_workshop_July_2019.pdf (3.14 MB)
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Extensions of the Application of MSE to Gulf Menhaden

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posted on 12.03.2021, 08:17 authored by Doug ButterworthDoug Butterworth, Rebecca A Rademeyer
This document provides extends the MSE simulation-testing process suggested for Gulf Menhaden in Rademeyer and Butterworth (2019) to make specific suggestions for a Management Procedure (MP) which would provide a basis to impose catch limitations on the fishery, though only when survey indices suggest that resource abundance has dropped further than is desirable. In particular, a reasonably large number of robustness tests has been developed to check if the MP (harvest control rule, which would set a catch limit based on recent values of abundance survey indices) provides robust performance (particularly as regards safeguarding the resource from undue depletion) in the face of assessment and other uncertainties. It transpires that for the current range of annual catch sizes, such a rule is really necessary only in the future circumstances of increasing natural mortality or a period of poor recruitment. A tuning criterion is put forward as a basis to compare the performances of different MPs (essentially different choices for the parameters of the harvest control rule). Finally, a suggestion is made for the value of one of these parameters (that of a composite survey abundance index) below which a catch limit would be imposed; higher values for this choice would lead to a greater frequency of (unnecessarily) imposing a catch limit, whereas lower values result in smaller values for lowest level of egg production expected and higher values of the average annual variability in landings. The composite survey index has been above the threshold value suggested for the last ten years.



Department of Mathematics and Applied Mathematics, University of Cape Town