Istituto di Scienze Marine     
Sala A., Lucchetti A., Perdichizzi A., Herrmann B., Rinelli P. Is square-mesh better selective than larger mesh? A perspective onthe management for Mediterranean trawl fisheries. In: Fisheries Research, vol. 161 pp. 182 - 190. Elsevier B.V, 2015.
Relatively little scientific work has been done to assess the selectivity of square-mesh codends in thehighly variable multi-species conditions in the Italian trawl fisheries. Therefore this study was initiatedto investigate the effect of using square-mesh and larger diamond-mesh codends on size selectivity ofdeepwater red shrimp (Aristaeomorpha foliacea) and red mullet (Mullus barbatus), with possible impli-cation in future management measures. Four different codends were used in the sea trials. When sizeselection estimates are applied for management issues it is not sufficient only to consider the mean sizeselection parameters. It also needs to consider the effect of between-haul variations in the selection pro-cess. In the current study, potential consequences of the between-haul variation on the selection curveshave been considered by applying a pooled curve with a double bootstrap approach. The results attainedin the present study indicate that the use of 40 mm square-mesh codend results in a 50% retention length(L50) similar to that of the 50 mm diamond-mesh codend, but with a steeper selection range (SR). For redmullet, both 50 mm diamond-mesh and 40 mm square-mesh codends lead to an L50 that is higher thanthe minimum landing size (MLS, 11 cm). Deepwater red shrimp is not subject to any MLS and may alwaysbe landed legally. However, large amounts of juveniles of deepwater red shrimp have been retained in allcodends. Council Regulation (EC) No. 1967/2006 called for a discard reduction policy in waters under thejurisdiction of the European Union. As demonstrated in the current paper, to simultaneously improve thesize selectivity of fish and shrimp species can be difficult due to large differences in their morphologicalcharacteristics, therefore it may question whether more sophisticated alternative of selective devices,such as grids or square-mesh panels, could be implemented in some Mediterranean fisheries.
URL: http://dx.doi.org/10.1016/j.fishres.2014.07.011
Subject selectivity
trawl fishery
Aristaeomorpha foliacea
Mullus barbatus

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