Selectivity of grid separator with horizontal bars for beam trawl fishery in Tokyo Bay [Japna]
2008
Ohata, S.(Chiba-ken. Fisheries Research Center, Futtsu (Japan). Tokyo Bay Fisheries Lab.) | Ikegami, N. | Nakamura, F. | Fujita, K. | Matsushita, Y.
Selectivity of a grid separator for marbled flounder Pleuronectes yokohamae and white-spotted conger Conger myriaster was estimated to reduce bycatch of juvenile marbled flounder while retaining commercial sizes of whitespotted conger. Four different grids made of horizontal bars (13, 15, 20 and 24 mm bar spaces) fixed on the belly of the codend were tested at sea from 2002 to 2004 to develop a measure for reducing bycatch. An external covernet was attached behind the grid to catch all fish that escaped through the grid. We used three different models (logistic, Richards, and contact-logistic models) to describe grid selectivity. The contact-logistic model was chosen as the best-fit model for marbled flounder and white-spotted conger. Grid selectivity was expressed as the ratio of vertical size of the fish body to bar space for both species. Under the test conditions, we considered that a grid of 15 mm bar space reduced juvenile discards of marbled flounder by 40% and caught most of the white-spotted conger.
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