Natuna Island is one of the small outer islands in Indonesia bordering Malaysia, Singapore, Thailand, Vietnam, and directly facing the South China Sea. Natuna seawaters have enormous potential fishery resources and one of the fishing areas used as a fishing activity for Indonesian and foreign fishermen. The potential also made illegal fishing practice rampant in Natuna seawaters and led to the Indonesian maritime security patrol being directed to Natuna seawaters to stop the illegal fishing process. The marine security patrol activities require high operational costs, and This can be minimized in several ways, particularly by knowing the points that can contain extensive fish resources, and the security patrols can be carried out directly at these points of location. To obtain information about these locations, map the potential fishing areas in Natuna seawaters for each period or monsoon. This study aims to apply remote sensing analysis to collect comprehensive information regarding strategic fishing areas prone to violations and security threats related to fishing activities based on monthly analyzes. The data used in this study were chlorophyll-a concentration and SST from MODIS level-3 with a resolution of 4 km from January to December 2019. SST and chlorophyll-a concentration data used pre-process analysis with SeaDas Software to ensure the data projection in the World Geodetic System (WGS) 84 format. The data processing stage uses ER Mapper software to project the distribution of SST and chlorophyll-a concentration into a contour. Post-processing data used ArcGIS software to determine crosses’ results on the SST contour and the combined chlorophyll-a concentration. Image data processing results show that the lowest fishing point on Natuna Island in August with 51 fishing points, and the highest fishing point on Natuna Island in February with 584 fishing points. The results showed that fishing points vulnerable to illegal fishing are mostly located in the northern part of Natuna Island. The fishing zone is mostly far from Natuna island’s coastal line. The results of this study indicate that the fishing area in the outer regions of Natuna Island needs to be increased in security and protection, especially in regions with a high level of fishing activity. This information is expected to become a reference for the authorities in the marine security sector in Natuna waters to take certain policies related to marine security patrols’ operational activities in Natuna waters, particularly in minimizing operational costs of marine security patrols in Natuna seawaters.
Several species of marine gastropod mollusk used by the community as economical food commodities, including the Strombus canarium was found in the Tanjung Sebauk, Bintan Island. The S. canarium diet as a deposit feeder significantly affects the consumption of the biota food varieties. Until now, there was limited information related to the classification of food consumed by S. canarium. Environmental factors affect S. canarium habitat substantially by providing a food source that is absorbed and influences the growth of S. canarium. Resettlement and restaurant activities in coastal areas affect changes in environmental conditions and modify the habitat and food variations of the organism. The Swept Area Sampling (SAS) method was applied to sweep and collecting S. canarium at a bed-ground area of 1500 m2 in Tanjung Sebauk. The shell splitting and surgery completion of S. canarium were handled in the laboratory. S. canarium samples were immersed with 10% formalin to serve and protect the gastric sample and prevent it from rupturing, including providing the possibility to observe the various food components from S. canarium. Each species of organism found in an S. canarium stomach sample was photographed and counted and measured three times. Photographs of the gastric sample obtained from observations in a microscope were analyzed and identified comprehensively to find the composition of food varieties from the S. canarium. The varieties of food composition obtained were distinguished by class and group of biota and analyzed using the Preponderance Index. The varieties of food composition in gastric samples from S. Canarium shown eight species with the majority composition from plankton groups (phytoplankton and zooplankton), and one species was the copepod class. The following species of biota found in the stomach S. canarium based on the Preponderance Index consisted of Thalassionema sp. (42.59%) as primary food, followed by Nocticula sp. and Coscinodiscus sp. as additional food with a percentage of 37.45% and 12.35%, respectively. In comparison, the variety of complementary food from S. canarium consisted of Entomoneis sp. (2.47%), Cymbella sp. (1.23%), Cochlodinium sp. (1.23%), Calanus sp. (1.85%), and Boreadinium sp. (0.82%).
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