This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

17Discards of regulated species in the Basque mixed trawl fishery are a challenge. In 2006, a square mesh 18 panel (SMP) was introduced in the fishery to increase the release efficiency of undersized fish. However, 19 studies have shown that the selectivity in this fishery is based on codend selectivity and the release 20 through the SMP is inefficient due to low contact between fish and the SMP. In order to improve contact, 21we tested four different gear configurations that use different stimulators to lead fish to the panel: without 22 stimulation, with stimulation based on ropes, with stimulation based on ropes and floats, and with 23 stimulation based on LED lights. The experiment was carried out on three of the potential choke species 24 for the fishery: hake (Merluccius merluccius), horse mackerel (Trachurus trachurus), and blue whiting 25 (Micromesistius poutassou). The results showed that stimulators did not significantly improve the release 26 efficiency of hake and horse mackerel through the panel. For blue whiting, stimulation with floats had a 27 significant positive effect on release efficiency, whereas LED light-based stimulation had the opposite 28 effect. In general, the contribution of the SMP to the overall release efficiency of the selective system 29 (SMP+codend) was low. Underwater recordings confirmed that the stimulators generally were not able to 30 lead fish towards the SMP. 31 Keywords: Square mesh panel (SMP); Basque bottom otter trawl; Release efficiency; Contact probability 32 33 *Manuscript including abstract Click here to view linked References et al. (2014) analyzed available data from observer discard monitoring, catch landings, and/or 53 nominal fishing effort from 2011 to 2013 and found that the total discard of the Spanish fleet 54 operating in ICES VIIIabd was around 60-65% of the total catch. Thus, unwanted catches and 55 discards constitute a substantial waste that negatively affects the sustainable exploitation of 56 marine resources (Kelleher, 2005). This perception has motivated the establishment of the 57 Landing Obligation (LO) under the provisions of Article 15 of the 2013 reform (EU, 2013). Its 58 main objective is to eliminate discards of commercially exploited stocks. By 2019, all EU 59fisheries are obliged to land the catches of regulated species to be counted against the quota. 60In recent decades, several fishing regulations have been implemented specifically to 61 stimulate the recovery of hake (ECminimum codend mesh size for trawlers fishing the northern stock of European hake in the Bay 63 of Biscay was changed from 70 mm to 100 mm diamond mesh. In 2006 (EC, 2006), fishermen 64 were given the alternative of using a 70 mm diamond mesh codend combined with a square 65 mesh panel (SMP) (2 m long, 1 m wide, 100 mm mesh size) inserted in the upper panel of the 66 extension piece of the trawl instead of a 100 mm diamond mesh codend. Currently, the gear 67 composed of the SMP with a 70 mm diamond mesh codend is the one most used by the fleet. 68Several studies have ...

Square mesh panels (SMPs) are selective devices used extensively to supplement codend size selectivity in trawl fisheries. Therefore, predictions of the effect of mesh size in both SMPs and codends on size selectivity are valuable. Here, we established a framework to predict the size selection of blue whiting through different SMPs and diamond mesh codends based on the morphological characteristics of this species. We hypothesized that size selection for an SMP is determined by different fish contact angles, whereas different mesh opening angles determine size selection for the codend. Based on these hypotheses, we first developed a model that enabled us to predict which sizes of blue whiting are able to pass through meshes of different sizes and shapes. We then tested whether the selectivity for blue whiting of the SMP, the codend, and the combination of both could be explained by the models. Finally, we predicted the size selectivity of multiple combinations of SMPs and diamond mesh codends. The method presented here can potentially be applied to make predictions for species other than blue whiting.

Reduction of discards from the Basque mixed bottom trawl fishery is a challenge. To improve the selective properties of the gear used by the fleet and supplement codend size selection, a square mesh panel (SMP) installed in the upper panel of the trawl was introduced in 2006. However, recent studies have shown that the release efficiency of this SMP is low due to lack of contact between the fish and the SMP. In this study, we tested the release efficiency of the SMP for four different gear configurations. We tested the effect of adding LED lights at two different positions and altering panel size and panel position in the trawl. The analyses were focused on two species: hake (Merluccius merluccius) and blue whiting (Micromesistius poutassou). The results showed that the position of LED lights did not significantly affect the SMP's release efficiency for any species. However, increasing panel size had a significant positive effect on the release efficiency of blue whiting, and placing the SMP in the lower panel improved the release efficiency of hake. These results highlight the challenge of simultaneously improving the selective properties of gear for species with different behaviour, especially in mixed demersal fisheries. Eficiencia de escape y selectividad de cuatro configuraciones diferentes aplicadas a un panel de malla cuadrada en la pesquería multiespecífica de arrastre del País VascoResumen: La reducción de descartes en la pesquería de arrastre del País Vasco supone un problema importante. En 2006, se introdujo en la reglamentación la posibilidad de usar un Panel de Malla Cuadrada (SMP) en la zona anterior al copo para mejorar la selectividad de la red. Sin embargo, estudios recientes manifiestan que la eficiencia de escape de los peces es baja debido a la falta de contacto selectivo entre el pez y el panel. En este estudio, analizamos la eficiencia de diferentes configuraciones del SMP. Se analizó el efecto de luces LED colocadas en distintas posiciones, el efecto del tamaño del SMP y su localización. Estudiamos la merluza (Merluccius merluccius) y la bacaladilla (Micromesistius poutassou). La posición de las LED demostró no tener ningún efecto significativo sobre la eficiencia de escape del SMP para ninguna de las dos especies. Sin embargo, aumentar el área del panel tuvo un efecto significativo en la eficiencia de escape de la bacaladilla, mientras que el cambio de posición del SMP incrementó la eficiencia de escape de la merluza a través del SMP. Estos resultados muestran el reto que supone mejorar la selectividad de un arte de pesca simultáneamente para especies demersales con comportamientos diferentes.Palabras clave: panel de malla cuadrada; luces LED; pesca de arrastre; eficiencia de escape; merluza; bacaladilla. Citation/Como citar este artículo: Cuende E., Arregi L., Herrmann B., Sistiaga M., Basterretxea M. 2020. Release efficiency and selectivity of four different square mesh panel configurations in the Basque mixed bottom trawl fishery. Sci. Mar. 84(1): 39-47. https://doi.org/10.3989/scimar.0...