Size selective capture of Atlantic cod (Gadus morhua) in floating pots |
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| Authors: | M Ovegård S Königson A Persson SG Lunneryd |
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| Institution: | 1. Department of Ecology, Ecology Building, Lund University, SE-223 62 Lund, Sweden;2. Institute of Coastal Research, Swedish Board of Fisheries, SE-453 21 Lysekil, Sweden;1. Department of Environmental Biology Fisheries Science, National Taiwan Ocean University, 2 Pei-Ning Rd., Keelung 20224, Taiwan, Republic of China;2. Center of Excellence for Oceans, National Taiwan Ocean University, 2 Pei-Ning Rd., Keelung 20224, Taiwan, Republic of China;1. University of Split, University Department of Marine Studies, Ru?era Bo?kovi?a 37, 21000 Split, Croatia;2. SINTEF Fisheries and Aquaculture, Fishing Gear Technology, Willemoesvej 2, 9850 Hirtshals, Denmark;3. University of Tromsø, Breivika, N-9037 Tromsø, Norway;1. NSW Department of Primary Industries, Fisheries Conservation Technology Unit, National Marine Science Centre, PO Box 4321, Coffs Harbour, NSW 2450, Australia;2. Department of Statistics, The University of Auckland, Private Bag 92019, Auckland, New Zealand |
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| Abstract: | Little is known about the size selectivity of cod in static fishing gears such as pots and traps. In this field study, floating fishing pots were equipped with 40, 45 and 50 mm square mesh escape windows in order to estimate the size selectivity of cod at different mesh sizes. Relationships between selectivity parameters and mesh size, as well as an optimal mesh size for the escape window with respect to current minimum landing size of cod in the Baltic Sea were sought. The results show that the floating pot is not only species selective when used in the Baltic Sea cod fishery, the implementation of an escape window reduced the proportion of undersized bycatch in the pots by more than 90%. The estimated length at 50% retention was found to be a direct function of fish body length (girth) and mesh size of the escape window, while the estimated selection range remained unchanged regardless of mesh size. Optimal mesh size, with respect to the length at 50% retention and current minimal landing size of 38 cm in the Baltic, was determined to be 45 mm. Strong indications (significant on the 0.01 probability level in the case of 50 and 40 mm escape windows) suggested that the relative fishing power of the pots increased with the implementation of an escape window. This result could be explained as a “saturation effect”, i.e. the probability of cod entering the pot is likely to be negatively dependent on cod density in the pot. The high species selectivity and the low catch rate of undersized fish have consolidated the floating pots position as a highly benign fishing method and the foremost alternative gear for the future coastal cod fishery in the Baltic Sea. |
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