Typology and behaviour of tuna aggregations around fish aggregating devices from acoustic surveys in French Polynesia |
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| Institution: | 1. Centre IRD de Bretagne, BP 70, 29280 Plouzané, France;2. Centre IRD de Montpellier, BP 5045, 34032 Montpellier cedex 1, France;1. Italian Institute for Environmental Protection and Research, Via Vitaliano Brancati, 60, 00144 Rome, Italy;2. Institute for the Coastal Marine Environment, National Research Council (CNR IAMC), Via Roma 3, 74100 Taranto, Italy;3. Regional Agency for Environmental Protection, Via Bologna 534, 44124 Ferrara, Italy;4. Department of Environmental Sciences, Informatics and Statistics, University Ca’ Foscari Venice, Campo della Celestia, 2737/b, I-30122 Venice, Italy;5. Institute of Marine Sciences, National Research Council (CNR ISMAR), Arsenale Tesa 104, Castello 2737/F, I-30122 Venice, Italy;6. Regional Agency for Environmental Protection, Via Lissa, 6, 30174 Venice, Italy;7. Regional Agency for Environmental Protection, Viale Ciusa 6, Cagliari, Italy;8. Shoreline, Area Science Park Padriciano 99, 34149 Trieste, Italy;9. Regional Agency for Environmental Protection, Via Don Bosco 4/F, 80141 Naples, Italy;10. Regional Agency for Environmental Protection, Via Adige 12, 57025 Piombino, Italy;11. Department of Biology, University of Naples Federico II, via Mezzocannone 16, 80134 Naples, Italy;12. Regional Agency for Environmental Protection, Via Federico II 41 – loc. Villa Potenza, 62010 Macerata, Italy;13. Regional Agency for Environmental Protection, Via Nairobi 4, 90100 Palermo, Italy;14. Regional Agency for Environmental Protection, Via Fiume 35, 58100 Grosseto, Italy;15. Regional Agency for Environmental Protection, Via Marradi 114, 57126 Livorno, Italy;p. Regional Agency for Environmental Protection, via Fontevivo 21, 19125 La Spezia, Italy;q. Department of Biology, University Tor Vergata, Via della Ricerca Scientifica, 00133 Rome, Italy;1. Laboratory of Ecology and Environment (L2E) (Unit Associated with the CNRST, URAC32), Faculty of Science Semlalia, Cadi Ayyad University, BP: 2390 Marrakech, Morocco;2. Laboratory of Biology and Biotechnology of Microorganisms, School of Science Semlalia, Cadi Ayyad University, BP: 2390 Marrakech, Morocco;1. NISEA, Fishery and Aquaculture Research Organisation, Salerno, Italy;2. AZTI, Txatxarramendi Ugartea z/g., E-48395 Sukarrieta, Bizkaia, Spain;3. Ifremer, Fisheries Ecol and Modelling Unit, F-44311 Nantes 03, France;4. Ifremer, University of Brest, CNRS, UMR 6308, AMURE, Unité d''Economie Maritime, IUEM, F-29280 Plouzane, France;5. DTU Aqua – National Institute of Aquatic Resources Technical, University of Denmark, Lyngby, Denmark;6. Thünen-Institute of Sea Fisheries, Bremerhaven, Germany;7. Joint Research Centre, Directorate D - Sustainable Resources, Unit D.02 Water and Marine Resources, Ispra, Italy;8. Sea Fish Industry Authority, EH7 4HS Edinburgh, UK;9. IoES, The Institute of Economic Studies, University of Iceland, Reykjavik, Iceland;10. Wageningen University and Research, Wageningen Economic Research, The Hague, the Netherlands;11. HCMR, Hellenic Centre for Marine Research, Attiki, Anavyssos, Greece;12. Fishor Consulting, Portsmouth, UK;13. IFRO, Department of Food and Resource Economics, Faculty of Science, University of Copenhagen, Denmark;1. Texas A&M University at Galveston, Galveston, TX, United States;2. LGL Limited, King City, ON, Canada;1. British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK;2. CCAMLR Secretariat, 181 Macquarie Street, Hobart, Tasmania 7000, Australia;3. Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Science, 106 Nanjing Road, Qingdao 266071, China;4. Australian Antarctic Division, Channel Highway, Kingston, Tasmania 7050, Australia;5. Institute of Marine Research, PO Box 1870, Nordnes, 5817 Bergen, Norway;6. Universidad de Los Lagos, Centro i∼mar, Camino a Chinquihue Km. 6, Puerto Montt CP 5502764, Chile |
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| Abstract: | Eighty-seven two-hour acoustic surveys (radius 0.8 nautical mile, vertical range 0–500 m) around 17 fish aggregating devices (FADs) were conducted in French Polynesia between December 1995 and February 1997. Associated tuna densities were calculated using two different techniques: echo counting when the fish had sufficient distances from each other and echo integration when the fish swam close together (in schools). No acoustic detection of tuna was observed during 27 of the 87 surveys, representing 81 % of all the nocturnal surveys and 15 % of the diurnal ones. The 60 other surveys showed three different classes of aggregations: (1) ‘deep scattered fish’, observed 45 times, (2) ‘intermediate scattered fish’, observed 16 times, and (3) ‘shallow schooling fish’, observed 16 times. Sometimes aggregations of different classes were observed beneath the same FAD. The size of the fish inside the aggregations (determined from target strength values), the distance between the individuals, and the depth of the fish all decreased from ‘deep scattered fish’ to ‘shallow schooling fish’ (100–300 m for ‘deep scattered fish’, 50–150 m for ‘intermediate scattered fish’, and above the depth of 50 m for ‘shallow schooling fish’). Fish densities also varied according to the class of aggregations: 7.3, 26, and 801 fish per km3 on average for ‘deep scattered fish’, ‘intermediate scattered fish’, and ‘shallow schooling fish’, respectively. The highest densities were observed during daytime, while night-time observations indicated a variety of situations, from the absence of individuals to large amounts of fish. |
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