Environmental Drivers of Skipjack tuna (Katsuwonus pelamis) Abundance in the Indian Ocean: Insights from Satellite Remote Sensing and Catch Data

Abstract

Skipjack tuna (Katsuwonus pelamis) is an economically and ecologically important fish species with a wide global distribution, particularly abundant in tropical oceans influenced by strong climatic variability. In the Indian Ocean, monsoonal cycle and mesoscale oceanographic processes produce rich upwelling areas that serve as productive fishing grounds. . Four-year satellite-derived environmental parameters, Sea Surface Temperature (SST), Sea Surface Chlorophyll (SSC), Sea Surface Height (SSH), Mixed Layer Depth (MLD), Sea Surface Salinity (SSS), and Eddy Kinetic Energy (EKE), data were obtained. These satellite data was merged with the catch data obtained from the Department of Fisheries and Aquatic Resources (DFAR) of Sri Lanka. The effect of the above oceanographic factors on skipjack tuna abundance and distribution was studied using the generalized additive model (GAM), and the empirical cumulative distribution function (ECDF). Findings showed clear seasonal and spatial variability with elevated CPUE consistently associated with moderate SST (26.5°C to 29.0°C), 0.00 mgm-3 to 0.50 mgm-3 of SSC, 0.35 m to 0.55 m of SSH, 0.00 m2s-2 to 0.90 m2s-2 of EKE, 31.5 PSU to 35.25 PSU of SSS, and 10.00 m to 27.50 m of MLD. The catch per unit effort (CPUE) shows variability in the main monsoon seasons of the Indian Ocean. These results showed SST, EKE, and SSC are important environmental parameters affecting the distribution and abundance of the skipjack tuna in the Indian Ocean. The EKE showed a strong association with the skipjack tuna catch rates when paired with the SST, suggesting that ocean eddies and sea surface temperature patterns play an important role in skipjack tuna distribution and abundance.