Theoretical study of the effect of round straps on the selectivity in a diamond mesh cod-end

Herrmann, Bent; Priour, Daniel; Krag, Ludvig Ahm

doi:10.1016/j.fishres.2006.04.018

Cited by 21 publications

(10 citation statements)

References 9 publications

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“…The design guides demonstrate the importance of mesh OAs during fishing. This effect of OA demonstrates that technical measures such as codend round-straps and lastridge ropes can affect L50 value because they restrict the codend meshes or help them open as the catch builds up during the fishing process (Herrmann et al 2006). For diamond mesh codends, the OA value is not completely fixed, as it can vary with location along the codend (Herrmann et al 2007) and is affected by the amount of catch (Herrmann 2005a,b).…”

Section: Discussionmentioning

confidence: 99%

The influence of mesh size and shape on the size selection of European hake (<em>Merluccius merluccius</em>) in demersal trawl codends: An investigation based on fish morphology and simulation of mesh geometry

et al. 2018

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European hake (Merluccius merluccius) is an important commercial species for several European bottom trawl fisheries. Therefore, understanding the influence of codend mesh size and shape on the size selection of European hake is critical for defining technical measures for fisheries targeting this species. Based on morphology data collected on European hake, the influence of mesh size and shape on bottom trawl codend size selectivity was investigated by simulation using the FISHSELECT methodology successfully applied previously for other species. The predicted size selection for European hake was found to agree well with previous experimental results for a wide range of mesh sizes if it was assumed that the codend meshes had a relatively small opening angle, between 20° and 40°, during trawling. This study enables detailed prediction of size selectivity for European hake and offers a potential explanation for previous experimental size selectivity results.

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Section: Discussionmentioning

confidence: 99%

The influence of mesh size and shape on the size selection of European hake (<em>Merluccius merluccius</em>) in demersal trawl codends: An investigation based on fish morphology and simulation of mesh geometry

et al. 2018

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“…Simulating the selective potential of the diamond-mesh cod end based on fish morphology.-Several studies have demonstrated that not only mesh size but also the openness of the meshes in diamond-mesh cod ends affects net selectivity (Herrmann 2005a(Herrmann , 2005bHerrmann and O'Neill 2005;Herrmann et al 2007;O'Neill and Herrmann 2007;Herrmann et al 2009). During trawling, the cod end meshes are stretched by hydrodynamic drag forces that act primarily on the accumulated catch in the aft end of the cod end (Herrmann 2005b;Herrmann et al 2006), where the mesh opening is unlikely to exceed 75 degrees. The same mesh state can be expected during the closing phase of the Danish seine fishing process, when the diamond-mesh netting is stretched and under tension due to pulling by the seine ropes.…”

Section: Methodsmentioning

confidence: 99%

Understanding and Predicting Size Selection in Diamond‐Mesh Cod Ends for Danish Seining: A Study Based on Sea Trials and Computer Simulations

et al. 2016

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Danish seining is an important fishing method used to harvest demersal species. Knowledge about the size selectivity of different demersal species with this type of fishing gear is therefore of importance for managing the exploitation of marine resources. However, there are only limited data on size selection in cod ends in this fishery. Sea trials were therefore carried out to collect size selectivity data for Atlantic Cod Gadus morhua, Haddock Melanogrammus aeglefinus, and Witch Flounder Glyptocephalus cynoglossus for a diamond‐mesh cod end. For all three species, the data were best described by a double logistic selection curve, implying that two different size selection processes occur in the cod end. The double selection process could be explained by an additional selection process occurring through slack meshes. The results imply that the escapement of 46% and 34% of the larger Atlantic Cod and Haddock (those above 48 cm), respectively, would be through wide‐open or slack meshes. Since these mesh states are only likely to be present in the latest stage of the fishing process (e.g., when the cod end is near the surface), a large fraction of the bigger fish probably escaped near the surface, which might influence their likelihood of survival. Furthermore, based on the models established for explaining the experimental size selection, we were able to predict the effect of changing the mesh size on cod end size selection in the Danish seine fishery. Received December 9, 2015; accepted February 18, 2016

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“…Roundstraps are known to affect selectivity of codends (Herrmann et al 2006). Because the codends were used in commercial activity, both codends had 24 mm diameter Danline round straps of ca.…”

Section: Sea Trialsmentioning

confidence: 99%

Estimating the selectivity of unpaired trawl data: a case study with a pelagic gear

et al. 2016

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Summary:Most selectivity experiments employ either the covered codend or paired gear methods. It is not always possible, however, to use these methods. Owing to operational, biological and/or environmental considerations, there may be no obvious way or it may be inappropriate to pair the test and control data. Hence, it will not be possible to estimate the selectivity of the gear and its uncertainty using standard statistical methods. This study presents a methodology for analysing the selectivity of fishing gears from unpaired test and control data. The uncertainty in the control and test population structures is accounted for by using a double bootstrapping procedure that takes into account both between-haul and within-haul variation. This bootstrapping approach is used to assess the selectivity of two different devices, a 139.5 mm T90 codend and a 135.9 mm codend with 140.9 mm lateral exit windows, in the Barents Sea pelagic cod trawl fishery. The purpose of the experiment was to test and compare the performance of the two devices in pelagic trawl fisheries, where high densities of fish can be encountered. Significant differences were detected between the T90 codend and the codend with the exit windows but only for sizes of cod between 55 and 76 cm.Keywords: trawl selectivity; pelagic fisheries; unpaired data; cod.Estimando la selectividad en redes de arrastre con lances no pareados: un caso de estudio con una red pelágica Resumen: La mayoría de los experimentos de selectividad emplean el método de copo cubierto o el de lances pareados. Sin embargo, la utilización de estos métodos no es siempre posible. En ocasiones, no se puede encontrar una manera lógica de emparejar los datos provenientes de lances de prueba y lances control, o esta puede ser inapropiada debido a consideraciones de tipo operacional, biológico o medioambientales. Por lo tanto, no sería posible estimar la selectividad de la red y la incertidumbre de los resultados obtenidos utilizando métodos estadísticos estandarizados. Este estudio presenta una metodología que facilita el análisis de la selectividad en artes de pesca en los que los datos provienen de lances no pareados. La incertidumbre en las estructuras poblacionales capturadas en los lances prueba y control se tiene en cuenta utilizando un método de doble "bootstrapping" que considera la variabilidad en cada lance y entre lances. Utilizamos este método de "bootstrapping" para estimar la selectividad de dos dispositivos diferentes en la pesca pelágica de bacalao del mar de Barents: un copo T90 con mallas de 139,5 mm y un copo con mallas romboidales de 135,9 mm con ventanas laterales de 140,9 mm. El propósito del experimento fue comparar el comportamiento de ambos dispositivos en la pesca de arrastre pelágico de bacalao, donde se pueden encontrar altas densidades de pescado. Se detectaron diferencias significativas entre el copo T90 y el copo con las ventanas pero solo para tallas de bacalao comprendidas entre 55 y 76 cm.

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Theoretical study of the effect of round straps on the selectivity in a diamond mesh cod-end

Cited by 21 publications

References 9 publications

The influence of mesh size and shape on the size selection of European hake (<em>Merluccius merluccius</em>) in demersal trawl codends: An investigation based on fish morphology and simulation of mesh geometry

The influence of mesh size and shape on the size selection of European hake (<em>Merluccius merluccius</em>) in demersal trawl codends: An investigation based on fish morphology and simulation of mesh geometry

Understanding and Predicting Size Selection in Diamond‐Mesh Cod Ends for Danish Seining: A Study Based on Sea Trials and Computer Simulations

Estimating the selectivity of unpaired trawl data: a case study with a pelagic gear

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