Behavior of different trawl codend concepts

Madsen, Niels; Hansen, Kurt; Madsen, Nina

doi:10.1016/j.oceaneng.2015.08.047

Cited by 24 publications

(16 citation statements)

References 23 publications

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“…The multiple small-volume objects mainly include waterfilled table tennis balls or small-volume water-filled bags. Madsen et al [18] used multiple small-volume water-filled bags to evaluate the effects of mesh types on the hydrodynamics and oscillations of the codend. Multiple small objects in the codend directly block the flow through the mesh, similar to the actual catch when investigating the flow field distribution.…”

Section: Effect Of Catch Substitutes On the Experimentsmentioning

confidence: 99%

“…However, these investigations explain the oscillation of the codend, but do not provide a method to minimize the oscillation amplitude or provide a model to fit the oscillation trend. Madsen et al [18] evaluated the behavior of six different codends at full scale in a flume tank of SINTEF and found that each codend oscillates considerably when loaded with fish, and the standard codend is the most stable of those six codends. Thus, he considered that adjusting the net type and combination mode of the codend can minimize its oscillation amplitude.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Cutting Ratio and Catch on Drag Characteristics and Fluttering Motions of Midwater Trawl Codend

Liu

Tang

You

et al. 2021

JMSE

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The codend of a trawl net is the rearmost and crucial part of the net for selective fish catch and juvenile escape. To ensure efficient and sustainable midwater trawl fisheries, it is essential to better understand the drag characteristics and fluttering motions of a midwater trawl codend. These are generally affected by catch, cutting ratio, mesh size, and twine diameter. In this study, six nylon codend models with different cutting ratios (no cutting, 6:1, 5:1, 4:1, 7:2, and 3:1) were designed and tested in a professional flume tank under two conditions (empty codends and codends with catch) and five current speeds to obtain the drag force, spatial geometry, and movement trend. As the cutting ratio of empty codends decreased, the drag force decreased, and the drag coefficient increased. The unfolding degree of codend netting and the height of empty codends were found to be directly proportional to the current speed and inversely proportional to the cutting ratio. The positional amplitude of codend with cutting ratio 4:1 was the smallest for catch. The drag force of codends with catch increased as the current speed increased, and first decreased and then increased as the cutting ratio decreased. To ensure the best stability and minimum drag force of the codend, it is recommended to use the 4:1 cutting ratio codend.

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Section: Effect Of Catch Substitutes On the Experimentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of Cutting Ratio and Catch on Drag Characteristics and Fluttering Motions of Midwater Trawl Codend

Liu

Tang

You

et al. 2021

JMSE

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“…Pope. 1975, Armstrong et al, 1990MacLennan, 1992;Wileman et al, 1996;Valdemarsen and Suuronen, 2001;Krag, 2009;Vasilakopoulos et al, 2011;Madsen et al, 2015;Stepputtis et al, 2015). The ecosystem approach to fisheries management, by incorporating both stock and ecosystem sustainability, triggered many discussions and debates on the need for more sophisticated management schemes and alternative selectivity concepts (Hall et al, 2000;Zhou et al, 2010;Rochet et al, 2011;Garcia et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

Modelling gear and fishers size selection for escapees, discards, and landings: a case study in Mediterranean trawl fisheries

Mytilineou

Herrmann

Mantopoulou-Palouka

et al. 2018

ICES Journal of Marine Science

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Gear selectivity and discards are important issues related to fisheries management but separately modelled. This work examines for the first time the overall size-selection pattern on the total amount of individuals of a species entering the trawl codend. An innovative approach was used based on modelling the escapement through the codend in the sea and the subsequently selection process by the fisher on the deck of the fishing vessel resulting into the discards and landings. Three different trawl codends and three species were investigated in the case study conducted. A dual sequential model accounting for both gear size-selectivity and the subsequent fisher-size-selectivity was applied, under the hypothesis that a fish entering the codend can follow a multinomial distribution with three probabilities, the escape, the discard and the landing probability, respectively. The model described the escape probability through the gear and the landing probability by the fisher as S-shaped curves leading to a bell-shaped curve for the discard probability affected by both gear and fisher selection. The model described well the experimental data in all cases. Sampling scheme of three compartments proved adequate. The model provides at the same time selectivity and discards parameters useful in fisheries management.

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“…Indeed, the codend hydrodynamics have as a non-negligible impact on its selection [1]. For instance, the codend fluttering motions lead to some changes in the codend mesh openings [2,3,4] and may have direct consequences on cleaner catches, knowing that the catch is correlated to the codend behavior [5,6,7]. The analysis of the high Reynolds turbulent flow around a moving codend remains a challenge for both experimental and numerical approaches.…”

Section: Introductionmentioning

confidence: 99%

Analysis of hydrodynamics of a moving trawl codend and its fluttering motions in flume tank

Druault

Germain

2016

European Journal of Mechanics - B/Fluids

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The coupled dynamics of the codend fluttering motion and its hydrodynamics behavior are investigated based on PIV measurements carried out around a 1/10 scaled model codend. The mean wake flow characteristics are firstly analyzed demonstrating the great effect of the codend motion. The differences in flow contour between fluttering motion and no-fluttering codend are highlighted by analyzing the classical mean characteristics of a body wake flow. In presence of fluttering motion, the classical results are recovered only if one considers the vertical extent of the codends oscillations as a reference length scale. Secondly, the frequency content of codend oscillations is analyzed and it is linked to the physical mechanisms. It is observed that the motion of the codend is mainly of a low-frequency activity and of another component related to the vortex shedding street. It is then demonstrated a complex fluidstructure interaction where the near wake hydrodynamics of the moving codend structure are an intricate interplay between the codend fluttering motion and the shear layer instabilities and large scale vortex shedding. The knowledge of such flow instabilities is of great importance to improve the understanding of the force acting on a trawl and for the implementation of some selected device to drive fish near the codend and then to reduce juvenile by-catch.

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Behavior of different trawl codend concepts

Cited by 24 publications

References 23 publications

Effect of Cutting Ratio and Catch on Drag Characteristics and Fluttering Motions of Midwater Trawl Codend

Effect of Cutting Ratio and Catch on Drag Characteristics and Fluttering Motions of Midwater Trawl Codend

Modelling gear and fishers size selection for escapees, discards, and landings: a case study in Mediterranean trawl fisheries

Analysis of hydrodynamics of a moving trawl codend and its fluttering motions in flume tank

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