Spatiotemporal distribution of albacore in relation to oceanographic variables in the Indian Ocean

The albacore tuna, Thunnus alalonga, is an economically important oceanic species widely distributed in the Indian Ocean. In this study, we examined the spatiotemporal distribution of albacore tuna with respect to remote sensing oceanographic variables, including sea surface temperature (SST), gradient SST (GSST) calculated from SST, sea surface sanity (SSS), and chlorophyll-a (Chl-a) during 2006 – 2016 using longline fishery data from the Indian Ocean Tuna Commission (IOTC). The monthly and yearly gravitational centers of catch per unit effort (CPUE) were calculated to represent the variability of local stock abundance on the fishing ground. Two clusters (concentrated and dispersed) of monthly gravitational centers were classified using K-means method. The distribution-habitat associations were quantitatively evaluated including SST between 20 and 27°C, GSST between 0.2 to 0.8 °C 10 km-1, SSS between 34.5 to 35.5 psu, and Chl a between 0.1 and 0.2 mg m−3. Two types of fishing ground, coast upwelling fishing ground (CUFG) and deep-sea frontal fishing ground (DFFG), were defined according to their location and oceanographic habitat. This study improves our understanding of the spatiotemporal dynamics of albacore tuna, which is critical for sustainable management of this important resources in the Indian Ocean.