69 Copyright © 2016, Indonesian Fisheries Research Journal (IFRJ) The Influence of Swimming Layer ……. in Eastern Indian Ocean (Rochman, F., et al.) Available online at: http://ejournal-balitbang.kkp.go.id/index.php/ifrj e-mail:ifrj.puslitbangkan@gmail.com INDONESIAN FISHERIES RESEARCH JOURNAL Volume 22 Nomor 2 December 2016 p-ISSN: 0853-8980 e-ISSN: 2502-6569 Accreditation Number: 704/AU3/P2MI-LIPI/10/2015 THE INFLUENCE OF SWIMMING LAYER AND SUB-SURFACE OCEANOGRAPHIC VARIABLES ON CATCH OF ALBACORE (Thunnus alalunga) IN EASTERN INDIAN OCEAN Fathur Rochman* 1 , Widodo Pranowo 2 and Irwan Jatmiko 1 1 Research Institute for Tuna Fisheries, Jl. Mertasari No. 140, Sidakarya, Denpasar Selatan, Denpasar, Bali – 80224. Indonesian 2 Research and Development Center for Marine & Coastal Resources, Jl. Pasir Putih II Ancol Timur, Jakarta. Indonesian Received; May 08-2015 Received in revised from Nov 29-2016; Accepted Nov 29-2016 ABSTRACT This study was highlighted the contenxt of albacore’s number catch, swimming layer and sub- surface oceanographic variables (SSOV) at Eastern Indian Ocean include temperature, dissolved oxygen, salinity, nitrate, phosphate and silicate. Hopefully the information would be useful for the longliners to understand the ALB behaviour, environment and the best techniques on how to catch this fish. Data in this study were based on the Research Institute for Tuna Fisheries (RITF) observer program in Benoa from 2010-2013. Data analysis was base on primary data and secondary data. Primary data are albacore’s (ALB) swimming layer data which are measured by minilogger. Secondary data is SSOV data which extracted from World Ocean Atlas 2009 (WOA09). The results show that the optimum catch of albacore occurred at depth of 118 to 291 m with the average temperature between 12.41-20.47 °C, dissolved oxygen 3.24-4.68 ml/l , salinity 34.78-35.01 psu, nitrate 6.78-17.50 μ mol/ l, phosphate 0.62-1.27 μ mol/l and silicate 10.06-24.77 μ mol/l. The highest catch of ALB was mostly at depth of 156 m (hook number 2 and 11) with the average temperature 18.71°C, dissolved oxygen 4.68 ml/l, salinity 34.78 psu, nitrate 10.71 μ mol/l, phosphate 0.86 μ mol/l and silicate 15.95 μ mol/l. The highest influence of swimming layer and sub-surface oceanographic variable to the number of ALB catch happened at depth of 291 m of ALB swimming layer with coefficient correlation (r) of 0.934 and determination coefficient (R 2 ) of 0.872. The lowest influence of swimming layer and sub-surface oceanographic variable to the number of ALB catch happened at depth of 156 m of albacore swimming layer with coefficient correlation (r) of 0.528 and determination coefficient (R 2 ) of 0.279.The relationship between swimming layer and sub-surface oceanographic variable on catch of ALB tuna was low (<0.500). Keywords: Swimming layer; sub surface oceanographic variable; albacore; Eastern Indian Ocean ___________________ correspondence author: e-mail: fathursmasabio1@gmail.com INTRODUCTION Albacore (ALB) is a temperate tuna, living mainly in the mid oceanic gyres of the Pacific, Indian and Atlantic Oceans (IOTC, 2014). In the Atlantic, their geographic limits are from 45-50° N and 30-40° S, while in the Indian Ocean, it’s distribution ranges from 5° N to 40° S with adults occurring from 5° N to 25° S (ISSF, 2014). According to IOTC, (2014), albacore is a highly migratory species, swimming for long distances during its lifetime (Chen et al., 2005). The ALB habit like that, because they are capable of thermo regulation, has high metabolic rate, and advance cardiovascular and blood/gas exchange systems. In the Pacific Ocean, migration, distribution availability, and vulnerability of ALB are strongly influenced by oceanographic conditions, especially oceanic fronts. Pre-adults (2–5 year old albacore) appear to be more migratory than adults. ALB tuna has vertical and horizontal movement (William et al ., 2014). The distribution and the abundant of ALB, are greatly influenced by oceanographic variables, such as temperature, swimming layers (depth of water), and nutrients (William et al ., 2014). The information of ALB distribution is very important to determine the successful of tuna catch operation (Barata et al., 2011). The main problem in catching ALB species is unknown its swimming layer stratification and accompanying phenomena related to the sub surface oceanographic variable (environment). This study