Using remote sensing of sea surface temperature (SST), sea surface height anomaly (SSHA) and chlorophyll-a (Chl-a) together with catch data, we investigated the detection and persistence of important pelagic habitat hotspots for skipjack tuna in the Gulf of Bone-Flores Sea, Indonesia. We analyzed the data for the period between the northwest and southeast monsoon 2007–2011. A pelagic hotspot index was constructed from a model of multi-spectrum satellite-based oceanographic data in relation to skipjack fishing performance. Results showed that skipjack catch per unit efforts (CPUEs) increased significantly in areas of highest pelagic hotspot indices. The distribution and dynamics of habitat hotspots were detected by the synoptic measurements of SST, SSHA and Chl-a ranging from 29.5° to 31.5°C, from 2.5 to 12.5 cm and from 0.15 to 0.35 mg m-3, respectively. Total area of hotspots consistently peaked in May. Validation of skipjack CPUE predicted by our model against observed data from 2012 was highly significant. The key pelagic habitat corresponded with the Chl-a front, which could be related to the areas of relatively high prey abundance (enhanced feeding opportunity) for skipjack. We found that the area and persistence of the potential skipjack habitat hotspots for the 5 years were clearly identified by the 0.2 mg m-3 Chl-a isopleth, suggesting that the Chl-a front provides a key oceanographic indicator for global understanding on skipjack tuna habitat hotspots in the western tropical Pacific Ocean, especially within Coral Triangle tuna.

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Large pelagic fish (LPF hereafter) is an important group of fishes targeted by local fishermen in the Indonesian Fisheries Management Area-713 (IFMA-713). This IFMA includes the Makassar Strait, Flores Sea, Bali Sea, and Gulf of Bone. The objective of this study was to identify the preferred oceanographic conditions based on LPF fishing grounds in the study area. The experimental fishing was conducted from April to September 2018 by using local commercial fisheries (pole and line and purse seine). The fishing base of pole and line vessels operating in the Gulf of Bone was at Murante fish landing site, Luwu Regency, South Sulawesi. On the other hand, the fishing base of purse seine vessels operating in the Makassar Strait was at Siddo fish landing site, Barru Regency, also in South Sulawesi. Oceanographic factors such as sea surface temperature (SST), sea surface chlorophyll-a (SSC) concentration, and depth were derived from satellite data. The LPF fishing grounds were analysed and visualize using Geographic Information System (GIS) techniques. Based on the results, LPF distributions tended to be the highest in specific oceanographic conditions, including SST of 30.0 - 31.0 °C and SSC of 0.20 - 0.30 mg.m−3. They were mostly found in nearshore and offshore areas (maximum depth of about 2,000 m). The selected oceanographic factors played an important role in explaining the LPF fishing grounds. This information could be used for spatial prediction of potential LPF fishing zones in relation to the fish distribution and abundance during the Southeast monsoon in the IFMA-713.

Skipjack tuna is an important fishery species, targeted by purse seine and handline fisheries in Makassar Strait. Fish distribution patterns are markedly influenced by several underlying oceanographic factors. This study aimed to assess the relationship between skipjack CPUE and some oceanographic variables, and map out the distribution pattern of this fish in the study area during January-May 2018. To meet these objectives, we combined satellite data of sea surface temperature (SST) and chlorophyll-a concentration (chl-a) with catch data. We used generalized additive models (GAMs) to explore skipjack abundance in relation to the oceanographic conditions and we employed the gravity centre of fishing ground movements to map the fish distribution pattern. Results indicate that SST and chl-a significantly influenced skipjack tuna CPUE. The fish schools were mostly located in the eastern Makassar Strait. In January skipjack schools were initially in Majene offshore waters and moved to Mamuju waters in February. The skipjack schools returned to the border area between Polman and Majene waters in March and then made a continuous migratory journey to the south-western areas of Barru and Pare-pare offshore waters in April. In May, the skipjack tuna returned to concentrate in southern areas of Majene waters. We proposed that the fish schools followed a clock-wise distribution movement pattern where the habitat displacements may have a link with the dynamic ranges of preferred oceanographic conditions (habitat hotspots). It is likely that these areas provide good feeding opportunities for skipjack tuna.

Makassar Strait has been identified as an area of interesting studies for marine science and operational fisheries. It provides the unique ocean structures such as topographic feature, the main path of the Indonesia Throughflow (ITF) and dynamics of thermal fronts.  The aims of this study were to map the dynamic spatial and temporal of the thermal fronts, and to describe their implications to the pelagic fisheries. We used satellite data of sea surface temperature (SST) for the period of January-December 2018 with spatial and temporal resolutions of 4 km and monthly, respectively. For fishery data, we used sampling data of skipjack tuna fishing ground distributions in October and December 2018.  Thermal fronts throughout the year were estimated using a Single Image Edge Detection (SIED) algorithm and the available fishing ground data were overlain on the SST front map.  The results showed that the spatial distributions of thermal fronts along Makassar Strait tended to be different every month. However, the thermal fronts were consistently detected near the upwelling area from June to September. Skipjack tuna fishing grounds associated with fish aggregating devices (FADs) developed in the northern area of upwelling in October. Two month later, the FADs and free swimming skipjack fishing grounds again well formed around the same location. It implies that the formation of the thermal fronts after upwelling contributes the positive effect on development of pelagic fishery especially skipjack in Makassar Strait.