Experimental and theoretical study of red mullet(Mullus barbatus)selectivity in codends of Mediterranean bottom trawls

Abstract

The objective of this study was to investigate the effect on Mullus barbatus (red mullet) codend selectivity by increasing the codend mesh size or reducing the number of meshes in the codend circumference. This was performed through experimental sea trials and computer simulations. The sea trials were carried out in the Adriatic Sea using a polyamide codend in order to assess its selectivity, to record morphological (height, width and length) and population size structure parameters of red mullet (Mullus barbatus). The selectivity process in the codend was also simulated with an individual-based model (PRESEMO) and a finite element model (FEMNET) to calculate the codend shapes. By adjusting the behavioural description of red mullet in the simulation, the model results reached an agreement with the experimental results. Next these, behavioural parameters were used in the simulation model to predict the effect of changing mesh size and number of meshes around in new codend designs. The predicted effect and the benefit of enforcing these designs on catch efficiency below and above minimum landing size (MLS) were investigated. The results confirm that the reduction of number of meshes in the codend circumference will be more beneficial than increasing the mesh size.

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“…Results clearly show that selectivity of previously used commercial codend is rather poor for mentioned species, and the narrow codend is significantly more selective. This finding is consistent with the results of the other studies conducted in the Mediterranean waters (Lök et al, 1997;Özbilgin et al, 2005;Sala et al, 2006;Kaykaç, 2007;Sala and Luchetti, 2010;. The only common species between the present and the other studies (Lök et al, 1997;Sala et al, 2006;Kaykaç, 2007;Sala and Luchetti, 2011) is the red mullet for which all the investigations clearly conclude that the narrow codend has higher L 50 values.…”

“…This finding is consistent with the results of the other studies conducted in the Mediterranean waters (Lök et al, 1997;Özbilgin et al, 2005;Sala et al, 2006;Kaykaç, 2007;Sala and Luchetti, 2010;. The only common species between the present and the other studies (Lök et al, 1997;Sala et al, 2006;Kaykaç, 2007;Sala and Luchetti, 2011) is the red mullet for which all the investigations clearly conclude that the narrow codend has higher L 50 values. However, because of the differences in the mesh material, mesh size, mesh diameter, presence and types of knots, number of meshes around the codend and tunnel, towing duration and populations fished, the results of the present study and the other investigations on the effect of codend circumference on selectivity are not directly comparable in terms of selection parameters.…”

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“…It was due to the number of meshes around codend circumference as in 40T1 and 44T2. Findings from narrow codends provide higher L50 values like for some other species given by different study conducted in the Mediterranean waters (Lök, Tokaç, Tosunoğlu, Metin, & Ferro, 1997;Özbilgin, Tosunoğlu, Aydin, Kaykaç, & Tokaç, 2005;Sala, Priour, & Herrmann, 2006;Kaykaç, 2007;Luchetti, 2010 and. On the other hand, 40T1 and 44T1 showed to come close to the length at first capture value of L50 12.7 and 13.2 cm, considering the size at LFM (13 cm) of bogue.…”

Towards the Introduction of Sustainable Fishery Products: The Bid of a Major Italian Retailer

“…In this multi-species fishery, even though all target species are subject to the same fishing effort, the less abundant and more vulnerable species may take a long time to recover from intense trawling activity. In addition, it has recently been documented that multi-species bottom trawl fisheries are characterized by high discard rates of undersized commercial species (i.e., juveniles, [39][40][41]) and accidental catches of non-target species with low or no market value, such as sharks, sea turtles, and marine mammals [42]. Thus, marine organisms at risk of decline may be caught together with species whose populations can withstand their fishing effort.…”