Modelling climate‐related variability of tuna populations from a coupled ocean–biogeochemical‐populations dynamics model

Abstract In the last five decades for which tuna fishing data are available, the interannual ENSO signal (SOI) and the related Pacific Decadal Oscillation (PDO) suggest two different regimes characterized by higher intensity and frequency of either El Niño or La Niña events. Recent estimates from a statistical population dynamics model (MULTIFAN‐CL) suggest that recruitment of three tuna species in the Pacific are correlated with these climate indices. While tropical tuna species like skipjack ( Katsuwonus pelamis ) and yellowfin ( Thunnus albacares ) had higher recruitments during El Niño events, the subtropical albacore species ( Thunnus alalunga ) showed the opposite pattern with low recruitment during El Niño and high recruitment during La Niña. The potential explanatory mechanisms for such relationships between recruitment and climate are investigated with a spatial environmental population model (SEPODYM). The model is a two‐dimensional coupled physical–biological interaction model at the ocean basin scale, and contains environmental and spatial components used to constrain the movement and the recruitment of tuna. Input datasets for the model are sea surface temperature, oceanic currents and new primary production that are simulated fields from a three‐dimensional coupled physical–biogeochemical model. The hypothesis that the spatial dynamics of temperature, currents (advection), food availability and predation constrain tuna recruitment is evaluated with an application of SEPODYM to skipjack. Simulation results showed that this hypothesis can reproduce fluctuations in the population that are similar to those estimated from the statistical model.