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Developing the Next Generation Tuna Stock Assessment Model
Developing the Next Generation Tuna Stock Assessment Model
Close-Kin Mark-Recapture (CKMR)
Tuna stocks worldwide are valuable resources that require reliable management advice to ensure their sustainability and produce reasonable yields and other benefits. Most stocks are monitored intensively and are assessed using contemporary methods such as age-structured integrated stock assessments. Some stocks are assessed using computer programs created specific for that stock, but most are assessed using general stock assessment programs. For example, Stock Synthesis (Methot and Wetzel, 2013) is used for the assessment of tropical tunas in the eastern Pacific Ocean by the IATTC, Pacific bluefin tuna by the ISC, and some stocks in the Indian Ocean by IOTC. Tropical tunas in the western and central Pacific Ocean are assessed using MULTIFAN-CL (Fournier et al., 1998; Hampton and Fournier, 2001), while other stocks are assessed using Stock Synthesis. There are also other general software packages that are used for assessing fish stock such as SAM, WHAM, CASAL, JABBA, a4a, and GADGET. More information about general stock assessment modes can be found in the papers published in the CAPAM special issue (https://www.sciencedirect.com/special-issue/10K0TPR2CL4) and the report from the workshop (Hoyle et al., 2020).
The currently used stock assessment programs are huge projects that have provided much needed science-based management advice, but they are unable to thoroughly accommodate new generation data (Close Kin Mark Recapture) or assumptions and modelling techniques that are now assumed necessary to generate improved management advice (e.g., random effects and fine scale spatial-temporal dynamics). The developers of these models are either retired or nearing retirement and adding new features is either near impossible or complicated. Therefore, it is time for the tuna assessment community to consider developing the next generation tuna stock assessment computer program.
There are several projects currently underway or complete to some degree to develop next generation models such as FIMS and CASTLE II, but it is not clear if these projects will deliver the type of computer program that is needed for tuna stock assessments nor whether the tuna assessment community can easily integrate into the projects to add the features that are desirable.
There are several major features that are considered desirable in tuna stock assessment models that might require consideration when designing the base structure of a general stock assessment program. This will help decide what approach should be followed for the next generation tuna assessments. The topics covered include: 1) Spatial structure; 2) Tagging data; 3) Length based dynamics; 4) Random effects; and 5) Close Kin Mark-Recapture. We will also cover: 6) The modeling framework and model components; and 7) Workflow in RTMB. As well as 8) lessons learned from previous developers.
The next generation general tuna stock assessment model should be considered in the context of the whole stock assessment ecosystem that includes a variety of components ranging from evaluating and testing assumptions, setting up input files, diagnostics, presenting results, and management strategy evaluation (Maunder 2024; see figure below). For example, using the general model in a simulation context can be used to evaluate model assumptions, create diagnostic algorithms, and implement management strategy evaluation.
Fournier, D.A., Hampton, J., Sibert, J.R., 1998. MULTIFAN-CL: a length-based, age structured model for fisheries stock assessment, with application to South Pacific albacore, Thunnus alalunga. Can. J. Fish. Aquat. Sci. 55, 2105–2116.
Hampton, J., Fournier, D.A., 2001. Aspatially disaggregated, length-based, age-structured population model of yellowfin tuna (Thunnus albacares) in the western and central Pacific Ocean. Mar. Freshw. Res. 52, 937–963.
Hoyle, S.D., Maunder, M.N., A’mar, Z.T. 2020. Frameworks for the next generation of general stock assessment models: 2019 CAPAM workshop report. New Zealand Fisheries Assessment Report 2020/39.
Maunder, M.N., 2024. Towards a comprehensive framework for providing management advice from statistical inference using population dynamics models. Ecol. Mod. 498, 110836 https://www.sciencedirect.com/science/article/pii/S0304380024002242
Methot, R.D., Wetzell, C.R., 2013. Stock Synthesis: a biological and statistical framework for fish stock assessment and fishery management. Fish. Res. 142, 86–99.
Illustration of a complete framework for stock assessment showing the components required in the next generation tuna stock assessment model and associated support programs (from Maunder, 2024).
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