# Climate-Driven Variation in Yellowfin Tuna Productivity in the Western and Central Pacific Ocean Inferred from a State-Space Model

## TL;DR

This study shows how climate factors like the Pacific Decadal Oscillation and ocean layer thickness affect yellowfin tuna productivity in the Pacific Ocean.

## Contribution

The study introduces a state-space model that incorporates environmental variables to assess yellowfin tuna productivity under climate change.

## Key findings

- Productivity estimates of yellowfin tuna show consistent temporal patterns but vary in magnitude based on model structure.
- The Pacific Decadal Oscillation and mixed layer thickness are positively linked to tuna productivity.
- Environmental variables can be effectively integrated into state-space models for better fisheries management.

## Abstract

Climate change is affecting ocean conditions and the productivity of pelagic fish populations, creating challenges for fisheries assessment and management. Yellowfin tuna (Thunnus albacares) is an important species in the western and central Pacific Ocean, where productivity varies over time in response to environmental variability. In this study, we applied a population model that allows productivity to change through time to examine the productivity dynamics of yellowfin tuna and their relationship with environmental variability. Different modeling scenarios were compared to evaluate uncertainties in productivity estimates and management reference points. We found that while temporal patterns of productivity were generally consistent, their magnitude and associated uncertainty depended on model structure. In addition, large-scale climate variability and ocean conditions, particularly the Pacific Decadal Oscillation and mixed layer thickness, were positively associated with tuna productivity. These results emphasize the importance of incorporating environmental information into fisheries assessments to support ecosystem-based management under climate change.

Understanding temporal variation in population productivity is critical for effective assessment and management of pelagic fish stocks under a changing climate. In this study, we applied a stochastic surplus production model in continuous time (SPiCT) with time-varying parameters to evaluate the productivity dynamics of yellowfin tuna (Thunnus albacares) in the western and central Pacific Ocean and to examine the influence of environmental variability on productivity. Multiple time-varying parameterization scenarios were explored to characterize uncertainties in productivity estimates and associated biological reference points. Generalized additive models were subsequently used to quantify the relationships between environmental variables and time-varying productivity. Results indicate that productivity estimates exhibit consistent temporal patterns across alternative modeling scenarios, while their magnitude and associated uncertainty are sensitive to model structure. Among the environmental factors examined, the Pacific Decadal Oscillation (PDO) and mixed layer thickness (MLT) showed consistent and statistically significant associations with maximum net productivity. Higher PDO values and greater MLT were both positively associated with population productivity. Overall, the results highlight the importance of environmental variability in shaping time-varying productivity of yellowfin tuna and demonstrate the feasibility of incorporating key environmental indicators into a state-space model. This approach provides a complementary framework for interpreting stock dynamics and supports the development of ecosystem-based fisheries management strategies in the western and central Pacific.