Release efficiency and selectivity of four different square mesh panel configurations in the Basque mixed bottom trawl fishery

Abstract

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...

Optimizing size selectivity and catch patterns for hake (Merluccius merluccius) and blue whiting (Micromesistius poutassou) by combining square mesh panel and codend designs

“…From experimental designs (i) and (ii), selectivity data for the SMP BS , SMP BL and CD D were obtained, whereas selectivity data for the CD S was obtained from design (iii). The selectivity data of SMP TS and SMP TL for hake and blue whiting was obtained from the sea trials conducted by Cuende et al [ 23 ] and Cuende et al [ 24 ], respectively. These two studies were carried out in 2017 and 2018 respectively, during same fishing period and similar fishing ground and depth.…”

“…These two studies were carried out in 2017 and 2018 respectively, during same fishing period and similar fishing ground and depth. Using information from the experimental sea trials in Cuende et al [ 23 , 24 ], the selectivity of all ten gear combinations was subsequently modeled.…”

“…The sea trials in the current and previous studies [ 23 , 24 ] included here were carried out on board the research vessel Emma Bardan (29 m length overall; 900 kW). The gear used in all experiments was a four-panel bottom trawl of the type GOC73 [ 53 ].…”

“…The release of fish through SMPs can be more problematic than through sorting grids or codend meshes because SMPs function by relying on fishes’ swimming ability and active contact with the SMP [ 21 – 24 ]. Some gear has been designed with the aim of improving fish contact with the SMP (e.g.…”

“…Contact probability can vary between species depending on SMP size and position in the trawl [ 21 , 26 ]. Cuende et al [ 24 ] showed that the release efficiency of hake through an SMP placed in the bottom panel of the extension piece was significantly higher than that of a larger SMP placed in the top panel of the extension piece, while for blue whiting ( Micromesistius poutassou ) the opposite result was achieved.…”