Selectivity and escape percentages during three phases of the towing process for codends fitted with different selection systems |
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| Authors: | E Grimaldo RB Larsen M Sistiaga N Madsen M Breen |
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| Institution: | 1. Norwegian College of Fishery Science, Breivika N-9037 Tromsø, Norway;2. Technical University of Denmark, Institute of Aquatic Resources, North Sea Science Park, DK-9850 Hirtshals, Denmark;3. FRS Marine Laboratory, 375 Victoria Road, Aberdeen AB11 9DB, Scotland, United Kingdom;1. SINTEF Fisheries and Aquaculture, Brattørkaia 17C, N-7010 Trondheim, Norway;2. BFE, Norwegian College of Fisheries and Aquatic Sciences, University of Tromsø, N-9037 Breivika, Tromsø, Norway;1. Consiglio Nazionale delle Ricerche (CNR), Istituto di Scienze Marine (ISMAR) [National Research Council (CNR), Institute of Marine Sciences (ISMAR)], Largo Fiera della Pesca, 60125 Ancona, Italy;2. Consiglio Nazionale delle Ricerche (CNR), Istituto per l’Ambiente Marino Costiero (IAMC) [National Research Council (CNR), Institute of Coastal Marine Environment (IAMC)], Sp. San Raineri 86, 98122 Messina, Italy;3. SINTEF Fisheries and Aquaculture, Fishing Gear Technology, Willemoesvej 2, 9850 Hirtshals, Denmark;1. NSW Department of Primary Industries, Fisheries Conservation Technology Unit, National Marine Science Centre, PO Box 4321, Coffs Harbour, NSW 2450, Australia;2. Marine and Estuarine Ecology Unit, School of Biological Sciences, University of Queensland, Brisbane, QLD 4072, Australia;3. Department of Statistics, The University of Auckland, Private Bag 92019, Auckland, New Zealand;1. NSW Department of Primary Industries, Fisheries Conservation Technology Unit, National Marine Science Centre, PO Box 4321, Coffs Harbour, NSW 2450, Australia;2. Marine and Estuarine Ecology Unit, School of Biological Sciences, University of Queensland, Brisbane, QLD 4072, Australia;3. Sterling Trawl Gear Services, 187 Ernest St., Manly, QLD 4179, Australia;4. Department of Statistics, The University of Auckland, Private Bag 92019, Auckland, New Zealand;1. School for Marine Science and Technology, University of Massachusetts Dartmouth, 706 South Rodney French Boulevard, New Bedford, MA 02744, USA;2. F/V North Star, 31 Vines Road, Saco, ME 04072, USA;1. Thünen Institute for Baltic Sea Fisheries, Alter Hafen Süd 2, Rostock 18069, Germany;2. SINTEF Fisheries and Aquaculture, Fishing Gear Technology, Willemoesvej 2, Hirtshals, 9850, Denmark;3. Swedish University of Agricultural Sciences (SLU), Department of Aquatic Resources/Institute of Marine Research, Turistgatan 5, Lysekil 453 30, Sweden;4. Norwegian College of Fishery and Aquatic Science, University of Tromsø, 9037 Breivika, Tromsø, Norway |
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| Abstract: | We investigated the selectivity of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) escaping from three different selection systems (a conventional diamond-mesh codend, a codend fitted with escape windows, and a codend fitted with a sorting grid) using the covered codend technique. By using a MultiSampler attached to the codend cover to partition the collection of escaping fish, we were able to determine the partitioned selectivity of each of these devices at different phases during the towing process: at depth, during the haul back, and at the surface.The percentages of escaping fish at depth from the diamond-mesh codend were significantly lower than those estimated for the escape windows and sorting grid codends: almost 62% of cod and 79% of haddock escaping from the diamond-mesh codend did so at depth, whereas approximately 75% of cod and 93% of haddock escaped from the other two systems at depth. The partitioned selectivity parameters, l50 and SR, were estimated and modelled for each of the three phases of the towing process and used to compare the selective properties of the three selection systems. A comparison was also made with a traditional whole haul selectivity analysis. Finally, bulk catch was added to the model as an explanatory variable and its effect upon selectivity was measured in both, partitioned and whole haul estimates. |
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