Selectivity of diamond- and square-mesh codends in the deepwater crustacean trawl fishery off the Balearic Islands (western Mediterranean)

Guijarro, Beatríz; Massutí, Enric

doi:10.1016/j.icesjms.2005.08.011

Cited by 88 publications

(119 citation statements)

References 26 publications

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“…Our L 50 estimated for hake with the 20-mm sorting grid (ca 13.3 cm) is close to that (14.2 cm) estimated earlier by Sardà et al (2005) with a similar 20-mm grid. However, our estimates of selection range (3.1 and 2.4 cm) are substantially smaller than theirs (7.3 cm), suggesting that small changes in rigging of the grid may cause major changes in SR. Our selectivity parameters for hake with the 40-mm square mesh (L 50 =18.5 cm, SR= 5.1 cm) were higher than those reported in the Balearic Islands (L 50 = 15.4 cm, SR = 4.5) (Guijarro and Massuti, 2006), probably due to the use in the islands of a thinner knotted PA netting operating in deepwater (>500 m) and at a lower speed (2.5 knots). The 20-mm sorting grid also came out as an effective selection device for red mullet.…”

Section: Mullus Barbatuscontrasting

confidence: 73%

The use of a square mesh codend and sorting grids to reduce catches of young fish and improve sustainability in a multispecies bottom trawl fishery in the MediterraneanEl uso de copo de malla cuadrada y rejillas separadas para reducir las capturas de pece

Sardà¹,

Bahamón²,

Molı́³

et al. 2006

Sci. Mar.

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SUMMARY: In order to improve the capacity of bottom trawl fishing gears to reduce catches of young fish and discards in a highly exploited demersal trawl fisheries in the Mediterranean, the size-selection performance of a 36-mm square-mesh codend and two sorting grids with 20 and 15 mm bar spacing was assessed. Alternate hauls were used to assess the selectivity of 36-mm square-mesh codend. Selectivity of sorting grids was assessed using a double codend in which fish that escaped through the grid were captured in the lower codend while other fish were guided into the upper codend. The mean selection length (L 50 ) for European hake was 18.5 cm and that for the Atlantic horse mackerel was 14.0 cm with the 36-mm square-mesh codend . These values are close to their current minimum landing sizes (20 cm for hake and 12 cm for horse mackerel). The sorting grid with 20-mm bar spacing showed L 50 value of 13.3 cm for hake, suggesting that a larger grid-spacing would be needed to obtain sufficient sorting performance. Similarly, for Atlantic mackerel the estimated L 50 of 14.3 cm indicates that larger grid spacing is required to attain an L 50 that would be close to the current MLS (18 cm). For Atlantic horse mackerel and red mullet, the L 50 obtained with the sorting grid with 20-mm bar spacing was close to the MLS of these species (the MLS of red mullet is 11 cm). The selectivity of the sorting grid with 15-mm bar spacing was generally very poor. Size-selection performance of sorting grids was assessed for the first time in the local fisheries. In order to effectively improve size-selection, seasonal and depth-dependent differences between target and by-catch species must be taken into account, which is a good indicator of the difficulty of implementing a single mesh size or grid spacing in the Mediterranean demersal trawl fishery.Keywords: Mediterranean Sea, sorting grid, square mesh, selectivity, multispecies fishery, bottom trawl, European hake, Atlantic horse mackerel, Atlantic mackerel, red mullet. RESUMEN: EL USO DE COPO DE MALLA CUADRADA Y REJILLAS SEPARADORAS PARA REDUCIR LAS CAPTURAS DE PECES JUVENILES Y MEJORAR LA SOSTENIBILIDAD DE UNA PESQUERÍA MULTIESPECÍFICA DE ARRASTRE DE FONDO EN ELMEDITERRÁNEO. -Con el propó-sito de mejorar la capacidad de las redes de arrastre de fondo para reducir las capturas de peces juveniles y descartes en una pesquería multiespecífica altamente explotada en el Mar Mediterráneo, se evaluó la selectividad de las tallas de diversas especies demersales mediante el uso de una malla cuadrada de 36 mm y dos rejillas con separación entre barras de 20 y 15 mm. Se usó el método de lances alternativos para evaluar la selectividad del copo de malla cuadrada. La selectividad de las rejillas se evaluó mediante un doble copo. Los peces que escaparon de la rejilla se capturaron en el copo inferior y el resto del pescado se guió y capturó en el copo superior. Con el copo de malla cuadrada, la talla media de madurez (L 50 ) de la merluza y el jurel fue respectivamente de 18,5 cm y 14,0 cm. Estos v...

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Section: Mullus Barbatuscontrasting

confidence: 73%

The use of a square mesh codend and sorting grids to reduce catches of young fish and improve sustainability in a multispecies bottom trawl fishery in the MediterraneanEl uso de copo de malla cuadrada y rejillas separadas para reducir las capturas de pece

Sardà¹,

Bahamón²,

Molı́³

et al. 2006

Sci. Mar.

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“…We accounted only for VMS signals from bottom trawlers, as these species are mainly caught with this type of gear in the study area. Only signals with speed between 1.5 and 5.0 knots were included, which correctly identify fishing activity (e.g., Guijarro and Massutí 2006). In order to account for the effect of fishing effort intensity on body condition, we averaged the sum of signals for each haul within a 3 km radius circle.…”

Section: Fishing Impactmentioning

confidence: 99%

Effect of intra‐specific competition, surface chlorophyll and fishing on spatial variation of gadoid's body condition

et al. 2015

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Abstract. Fish condition indices can be used as biological indicators of the health of individuals and are influenced by numerous external and internal drivers. Like most essential biological traits, they are very sensitive to the spatial heterogeneity occurring in marine ecosystems, which appears at many observational scales. This brings out different ecological processes that can only be revealed either regionally or locally. The scale-dependent spatial variability concerns not only environmental factors, but also anthropogenic activities such as fishing. Understanding these relationships is crucial for improving the spatial management of marine resources, because fish condition considerably affects the sustainability of populations. We explore the influence of density-dependent (intra-specific competition) and densityindependent variables (surface chlorophyll a concentration and fishing impact) on fish condition of three species of harvested gadoids (Merluccius merluccius, Phycis blennoides and Micromesistius poutassou) of the benthopelagic communities off the Balearic Islands (western Mediterranean). This area is characterized by high spatial heterogeneity in the environmental processes and fishing impact. Results show contrasting responses in body condition to the investigated covariates, with species-specific and ontogenetic differences sensitive to the spatial scale of analysis. Some of these responses occur at regional level, while others are more sensitive to local variation. Intra-specific competition shows a very clear effect, which depends on the ontogeny, identifying aggregation areas for recruits and limitation of resources for older individuals. Surface chlorophyll a has always a species-specific regional effect, despite gadoids have a more benthic behavior. Fishing effort displays a heterogeneous impact on fish condition. While spatially contrasting effects are observed at local scale, non-linear regional patterns occur, with positive effects of fishing pressure at intermediate levels. Models analyzing the influence of external drivers in essential fish biological traits such as body condition should consider the spatial variation in responses, especially in highly heterogeneous areas where anthropogenic activities occur. Failing to do so may hide local ecological processes that can be crucial for the persistence of fish populations, which is of paramount relevance for the regional assessment and spatial management of marine exploited resources.

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“…Therefore, many researchers have suggested increasing the mesh size and/or changing the mesh shape in the codend. Many studies outside the aegean sea have shown that an increase in mesh size and a change of mesh shape in the trawl codends reduce the number of juvenile P. longirostris caught (sobrino et al, 2000;guijarro and Massutí, 2006;Rinelli et al, 2005;Ragonese and bianchini, 2006). in addition, the general Fisheries Commission for the Mediterranean (gFCM) has encouraged studies aimed at improving selectivity and reducing the discards of this fleet (gFCM 2007).…”

mentioning

confidence: 99%

Selectivity of commercial, larger mesh and square mesh trawl codends for deep water rose shrimp <em>Parapenaeus longirostris</em> (Lucas, 1846) in the Aegean Sea

2009

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sUMMaRy: We investigated the differences between size selectivity of a commercial codend (40 mm diamond mesh -40d), a larger mesh codend (48 mm diamond mesh -48d), and a square mesh codend (40 mm square mesh -40s) for Parapenaeus longirostris in international waters of the aegean sea. selectivity data were collected by using a covered codend method and analysed taking between-haul variation into account. The results indicate significant increases in l 50 values in relation to an increase in mesh size and when the square mesh is used in the commercial trawl codend. The results demonstrate that the commercially used codend (40d) is not selective enough for P. longirostris in terms of length at first maturity. Changing from a 40d to a 48d codend significantly improves selection, with an increase of about 15% in the l 50 values (carapace length 14.5 mm for 40d and 16.6 mm for 48d). similarly, 40 mm square mesh, which has recently been legislated for eU Mediterranean waters, showed a 12.4% higher mean l 50 value (16.3 mm) than 40 mm diamond mesh for this species. However, despite these improvements, the 48d and 40s codends still need further improvements to obtain higher selectivity closer to the length at first maturity (20 mm carapace length).Keywords: Parapenaeus longirostris, mesh size, mesh shape, diamond mesh, square mesh.ResUMen: Selectividad para malla más grande y malla cuadrada de los copos comerciales en la pesca de la gamba blanca ParaPenaeus longirostris (Lucas, 1846) en el mar Egeo. -se estudian las diferencias entre la selectividad de los copos comerciales (40 mm de malla de diamante -40d); copos de malla más grande (48 mm de malla de diamante -48d), y copos de malla cuadrada (40 mm -40s), en la pesquería de Parapenaeus longirostris en aguas internacionales del mar egeo. Para su estudio se utilizó el método del sobrecopo, y para su análisis, se tuvo en cuenta la variación intra-lances. los resultados indican un incremento de los valores de l 50 cuando se incrementa el tamaño de malla, y también con el uso de la malla cuadrada. los resultados demuestran que el copo comercial actual (40d), no es suficientemente selectivo para P. longirostris en relación a la talla de primera madurez. el cambio, la malla de 48d, produce una mejora significativa en la selectividad cercana al 15% de incremento en los valores de la l 50 (longitud del caparazón de 14.5 mm para 40d y 16.6 mm para 48d). igualmente, la malla 40s, la cual ha sido legislada recientemente por la Ue en aguas del Mediterráneo, muestra un incremento de la selectividad aproximadamente de un 12% en los valores de la l 50 (16.3 mm) respecto a la de 40d. no obstante, a pesar de estas mejoras, los copos de 48d y 40s, todavía deberían ser ampliados para obtener selectividades más elevadas y acercarse a la talla de primera madurez (20 mm de caparazón).Palabras clave: Parapenaeus longirostris, tamaño de malla, forma del malla, rombo, malla cuadrada. , 597-604, barcelona (spain) issn: 0214-8358 Scientia Marina73(3) september 2009

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Selectivity of diamond- and square-mesh codends in the deepwater crustacean trawl fishery off the Balearic Islands (western Mediterranean)

Cited by 88 publications

References 26 publications

The use of a square mesh codend and sorting grids to reduce catches of young fish and improve sustainability in a multispecies bottom trawl fishery in the MediterraneanEl uso de copo de malla cuadrada y rejillas separadas para reducir las capturas de pece

The use of a square mesh codend and sorting grids to reduce catches of young fish and improve sustainability in a multispecies bottom trawl fishery in the MediterraneanEl uso de copo de malla cuadrada y rejillas separadas para reducir las capturas de pece

Effect of intra‐specific competition, surface chlorophyll and fishing on spatial variation of gadoid's body condition

Selectivity of commercial, larger mesh and square mesh trawl codends for deep water rose shrimp <em>Parapenaeus longirostris</em> (Lucas, 1846) in the Aegean Sea

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