Citation: Cai, K.; Kindong, R.; Ma, Q.; Tian, S. Stock Assessment of Chub Mackerel (Scomber japonicus) in the Northwest Pacific Using a Multi-Model Approach. Fishes 2023, 8, 80. https://doi.org/10.3390/ fishes8020080 Academic Editors: Fabio Fiorentino and Manuel Otilio Nevárez Martínez Received: 30 November 2022 Revised: 16 January 2023 Accepted: 28 January 2023 Published: 30 January 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). fishes Article Stock Assessment of Chub Mackerel (Scomber japonicus) in the Northwest Pacific Using a Multi-Model Approach Kai Cai 1,† , Richard Kindong 1,2,3,† , Qiuyun Ma 1,2,3, * and Siquan Tian 1,2,3 1 College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, China 2 National Engineering Research Center for Oceanic Fisheries, Shanghai Ocean University, Shanghai 201306, China 3 Key Laboratory of Sustainable Exploitation of Oceanic Fisheries Resources, Ministry of Education, Shanghai 201306, China * Correspondence: qyma@shou.edu.cn † These authors contributed equally to this work. Abstract: Chub mackerel (Scomber japonicus) is a major targeted species in the Northwest Pacific Ocean, fished by China, Japan, and Russia, and predominantly captured with purse seine fishing gear. A formal stock assessment of Chub mackerel in the region has yet to be implemented by the managing authority, that is, the North Pacific Fisheries Commission (NPFC). This study aims to provide a wider choice of potential models for the stock assessment of Chub mackerel in the Northwest Pacific using available data provided by members of the NPFC. The five models tested in the present study are CMSY, BSM, SPiCT, JABBA, and JABBA-Select. Furthermore, the influence of different data types and input parameters on the performance of the different models used was evaluated. These effects for each model are catch time series for CMSY, catch time series and prior of the relative biomass for BSM, prior information for SPiCT, and selectivity coefficients for JABBA-Select. Catch and CPUE (catch per unit effort) data used are derived from NPFC, while some life history information is referred from other references. The results indicate that Chub mackerel stock might be slightly overfished, as indi- cated by CMSY (B 2020 /B MSY = 0.98, F 2020 /F MSY = 1.12), BSM (B 2020 /B MSY = 0.97, F 2020 /F MSY = 1.21), and the base case run for the JABBA-Select (SB 2020 /SB MSY = 0.99, H 2020 /H MSY = 0.99) models. The results of the models SPiCT (B 2020 /B MSY = 2.30, F 2020 /F MSY = 0.31) and JABBA (B 2020 /B MSY = 1.40, F 2020 /F MSY = 0.62) showed that the state of this stock may be healthy. Changes in the catch time series did not affect CMSY results but did affect BSM. The present study confirms that prior information for BSM and SPiCT models is very important in order to obtain reliable results on the stock status. The results of JABBA-Select showed that different selectivity coefficients can affect the stock status of a species, as observed in the present study. Based on the optimistic stock status indicated by the best model, JABBA, a higher catch is allowable, but further projection is required for specific catch limit setting. Results suggested that, as a precautionary measure, management would be directed towards maintaining or slightly reducing the fishing effort for the sustainable harvest of this fish stock, while laying more emphasis on accurately estimating prior input parameters for use in assessment models. Keywords: data limited methods; CMSY; BSM; SPiCT; JABBA; JABBA select; models comparison 1. Introduction Chub mackerel (Scomber japonicus), a pelagic migratory fish, is widely distributed in the Indian Ocean and the Pacific Ocean [1]. There are two cohorts of Chub mackerel in the Northwest Pacific Ocean: the Tsushima cohort, and the Pacific cohort [2,3]. The Tsushima cohort is located on the western side of the Japanese landmass, mainly distributed from the northern part of the Sea of Japan to the southern part of the East China Sea, while the Pacific cohort is distributed along the southern coast of Japan, on the eastern side of the Japanese landmass, as far east as the sea around 170 ◦ E[2,3]. The Pacific cohort of this species is an Fishes 2023, 8, 80. https://doi.org/10.3390/fishes8020080 https://www.mdpi.com/journal/fishes