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The reference operating model for the Indian Ocean swordfish stock was developed over the last two years and has been endorsed by the IOTC scientific committee. The OM was based on the 2019 WPB SS3 assessment, and covered the dynamics of the swordfish until the year 2018. This OM was updated to the year 2021, by projecting the stock forward based on the reported catches for 2019 and 2020.
Further developments to the swordfish MSE were made in 2022 and included the development and application of two types of candidate MPs, one model based and one data based, and the tuning of these MPs (i.e. defining the MP parameters that achieve a certain management goal) for a range of management objectives over the next 11 to 15 years. Preliminary results were presented at the 2022 TCMP-05.
Examination of the first MSE runs showed that tunning objectives were achieved (mean p(Green) at 0.5, 0.6 or 0.7) but there was a large variability in p(Green) between simulation iterations (i.e. the 25th-75th quantile interval ranges from 0 to 1). This came from the fact that the choices made when assembling the reference OM (i.e. the grid of stock assessment assumptions used) resulted in a very wide range of stock dynamics and initial stock status.
In this document, we briefly present the results of these preliminary MSE runs to illustrate the implications of using a OM with a very wide range of initial stock status, show how this large variability in the starting conditions is a consequence of some of the choices made when constructing the structural uncertainty grid of the reference OM, and test a narrower range of assumptions to construct an OM in an attempt to develop a more suitable basis for conducting a MSE.
