Environmental signal in skipjack tuna recruitment in the Indian Ocean

Skipjack is a tuna species that is known to respond quickly to environmental changes. The active search of prey is a requirement for this species which needs to sustain high metabolic rates. The ocean productivity is driven by physical processes that exhibit inter-annual fluctuations and cycles. Phytoplankton biomass at the sea surface is measured in routine from the space by specific sensors, whereas the secondary production which composes the diet of larvae, is only measured in situ, or is derived through biogeochemical coupled models. Here, we use the satellite-measured sea surface chlorophyll as a proxy of ocean productivity and we examine its relationship from 1998 to 2018 with annual recruitment deviates estimated by the SS3 assessment model run at the last skipjack stock assessment of the IOTC in 2020. We show 1) that multi-year oscillations occur in both series; 2) that these oscillations occur in synchrony; and 3) that the Indian Ocean dipole appears to play a leas a key environmental driver of the system.