Environmental variations on swordfish (Xiphias gladius) catch rates in the Indian Ocean

The environmental processes associated with the climatic oscillations that drive variability in swordfish catch rates are largely unexplored. This study used generalized additive models fitted to longline fishery data to investigate relationships between environmental variables and catch rates to understand the processes influencing swordfish distributions in the Indian Ocean. The catch rates and distribution of swordfish in the Indian Ocean were sensitive to climatic and environmental variation. The environmental effects differ between the northwest and southwest Indian Ocean. The predicted relative abundance reveals a notable increase along the western coast of the northwest Indian Ocean during nominal Indian Ocean Dipole and negative Southern Indian Ocean Dipole (IOSD) events, and is related to the changes in net primary production and shallow mixed layer depth. The predicted relative abundances also show that the distribution of lower sea surface temperature and sea surface height deviation surrounding Madagascar increased during negative IOSD events in the southwest Indian Ocean.