Climatic oscillations effect on the yellowfin tuna (Thunnus albacares) Spanish captures in the Indian Ocean

The yellowfin tuna (Thunnus albacares) (YFT) is among the eight marine species with
the highest catches globally. The Spanish purse seine freezer fleet operating in the
Indian Ocean is one of the most important YFT fishing fleets in the world. The South
Oscillation Index (SOI), Pacific Decadal Oscillation (PDO), and Indian Ocean Dipole
(IOD) are interrelated, and have combined effects in the Indian Ocean. Moreover,
Madden–Julian Oscillation (MJO) is the dominant component of intraseasonal variability
in the tropical Indian and Pacific oceans where the sea surface is warm. The
main aim of present study is to understand the effect of these four climatic oscillations
on Spanish purse seine YFT catches in the Indian Ocean. The ultimate goal is
to estimate the specific time lag of the effect of each climatic oscillation on the YFT
catches for management purposes. To estimate this, we adjusted different General
Additive Models between the response variable (corrected YFT catches per unit of
effort per year), compared to a combination of SOI, PDO, IOD, and MJO lagged up
to 8 years. Our results suggest that there is a lagged effect modulated mainly by
PDO-SOI, which could be related to a good recruitment, larval survival, or improved
spawning. Thus, negative PDO phase (or positive SOI phase) lagged between 3 and
6 years could favor future stock abundance, while positive PDO phase (or negative
SOI phase) lagged 3 or 6 years could negatively affect future stock abundance.