Alternative stock assessment of Pacific saury in the western North Pacific Ocean using JABBA

The participants of the 3rd Meeting of the Technical Working Group on Pacific Saury Stock Assessment (TWG PSSA03) agreed that stock assessment working papers must include 12 scenarios (six base cases and six sensitivity cases) and may include models fit to nominal joint CPUE. Such models are for exploration only and will not be used as sensitivity analyses in the preliminary assessment (TWG PSSA03 Report). This paper doesn’t include those 12 scenarios, but instead it includes one optional model fit to nominal joint CPUE and biomass estimate through Japanese fishery independent survey.
The goal of this research is to make the evaluation as much reproducible as possible using the data available to the Secretariat of the NPFC. With this regards we tried to evaluate the stock status of the Pacific saury (Cololabis saira) in a new, open-source modelling software entitled ‘Just Another Bayesian Biomass Assessment’ (JABBA). JABBA is used to model biomass dynamic and has emerged from the development of a Bayesian State-Space Surplus Production Model framework, already applied in stock assessments of sharks, tuna (IOTC and ICCAT), billfishes and NOAA Hawaii Kona crab benchmark assessment (Winker et al. 2018). The software for JABBA is publicly available online at https://github.com/Henning-Winker/JABBAbeta. We used the latest version 1.2, so anyone can fully reproduce presented results.
We confirm the conclusion of TWG-PSSA first meeting report that B-ratio and F-ratio are mostly in the safe zone (green box of Kobe plot).