Lag effect of the El Niño–Southern Oscillation on the catch per unit effort of Yellowfin Tuna and Bigeye Tuna in the western and central Pacific longline fisheries

ABSTRACT Objective Yellowfin Tuna Thunnus albacares and Bigeye Tuna T. obesus are highly migratory pelagic species and major targets of distant-water fisheries worldwide. The distribution and abundance of their populations are highly susceptible to environmental variability caused by climate change, with notable time lags in response. However, such lagging effect still remains unclear, which imposes challenges to the fishery management of those populations of ecological and commercial importance. Methods This study therefore uses a Transformer model to analyze the influence of the Oceanic Niño Index (ONI) on the catch per unit effort (CPUE) of Yellowfin Tuna and Bigeye Tuna caught by longline fisheries in the western and central Pacific Ocean (WCPO) from 1978 to 2021 to explore the impact of climate change on the adult Yellowfin and Bigeye Tuna populations in the WCPO and its lagging effect further. The study simulates the response of CPUE to ONI under different lag periods (0–60 months). Results The results indicate Transformer’s suitability for analyzing lag effects between characteristics of these populations and climatic index like the ONI. Also, the CPUE shows a delayed response to the ONI, with the lag period being related to their life histories, and exhibits both short-term (within 3 months) and long-term (1–3 years) lag responses to the ONI. Conclusions As the lag period increases (40 months), the response of CPUE to the ONI weakens gradually. The findings and the methodology underpinning this work provide new insights into the mechanisms of resource fluctuations for the populations of key species in the WCPO.