Impacts of temporal growth variability on fisheries stock assessment in changing oceans: a case study of Eastern Atlantic skipjack

Ji Feng ^1* Fan Zhang ¹ Ming Sun ² Yong Chen ² Jiangfeng Zhu ^1*

• ¹ Shanghai Ocean University, Shanghai, China
• ² Stony Brook University, Stony Brook, New York, United States

Climate change affects the somatic growth of many important fish species targeted by fisheries worldwide, yet the explicit incorporation of climate-driven temporal growth variation in assessment remains limited for most fisheries stocks. In this study, we use Eastern Atlantic skipjack (Katsuwonus pelamis) as a case study to explore the effects of misspecifying temporal growth variation driven by sea surface temperature on stock assessments, highlighting the potential risks associated with neglecting temporal growth variation under both historical and future climate conditions. Misspecification of temporal growth variation in stock assessment models is found to introduce bias in the estimated quantities of interest in informing fisheries management, regardless of whether the "true" growth varies with time. Our findings indicate that the estimated quantities of management interest, in particular, the SSB-associated quantities (e.g., stock depletion) are more sensitive to the inclusion of time-varying Linf than to timevarying K. We emphasize the importance of incorporating temporal variation in fish asymptotic length into the stock assessments of Eastern Atlantic skipjack under the effects of future climate change. Consequently, integrating environmental data into stock assessment is necessary for climate-adaptive stock assessment and fisheries management.