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

2021 ◽  
Vol 9 (3) ◽  
pp. 256
Author(s):  
Wei Liu ◽  
Hao Tang ◽  
Xinxing You ◽  
Shuchuang Dong ◽  
Liuxiong Xu ◽  
...  
Keyword(s):  
Drag Force ◽  
Mesh Size ◽  
Current Speed ◽  
Midwater Trawl ◽  
Minimum Drag ◽  
Fish Catch ◽  
Spatial Geometry ◽  
By Catch ◽  
Trawl Fisheries ◽  
Crucial Part

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.

The Effect on Juvenile Haddock By-catch of Changing Cod-end Twine Thickness in EU Trawl Fisheries

1999 ◽  
Vol 33 (2) ◽  
pp. 61-72 ◽  
Author(s):  
Robert J. Kynoch ◽  
Grietje Zuur
Keyword(s):  
European Commission ◽  
North Sea ◽  
Mesh Size ◽  
Melanogrammus Aeglefinus ◽  
Sea State ◽  
Significant Difference ◽  
By Catch ◽  
Trawl Fisheries ◽  
Haddock Melanogrammus Aeglefinus

The selectivity of North Sea haddock (Melanogrammus aeglefinus) was measured for 100 mm mesh trawl cod-ends made of three different twines: 4 mm double twine used commercially until the introduction of thicker twines during the 1990’s; 6 mm double twine and 8 mm single twine proposed by the European Commission as maximum thicknesses starting in January 2000. A significant difference in selectivity was found between the 4 mm double twine and the two thicker, stiffer twines. The 50% retention length was increased by almost 4 cm when using the thinner twine. Models of the selectivity of these cod-ends have been developed, taking into account small mesh size differences and using catch size as a variable and sea state and twine size as categorical variables.The benefits of using a thinner twine cod-end are illustrated by showing the effect on the catch of juvenile and marketable fish from a typical North Sea population of haddock. The potential increases in survival of the 2 + and 3 + year classes of such a haddock stock are estimated to be 17% and 12% respectively.

Effects of an increase in mesh size on the catches of fish trawls off New South Wales, Australia

1995 ◽  
Vol 46 (4) ◽  
pp. 745 ◽  
Author(s):  
MK Broadhurst ◽  
SJ Kennelly
Keyword(s):  
New South ◽  
New South Wales ◽  
Mesh Size ◽  
The Body ◽  
South Wales ◽  
Large Numbers ◽  
By Catch ◽  
Species Specific ◽  
Trawl Fisheries ◽  
Future Management

In response to claims that fish trawls off New South Wales, Australia, caught excessive quantities of under-size fish, the catches of finfish by a conventional fish trawl (constructed of 90-mm mesh in the body) were compared with those by a fish trawl constructed of 100-mm mesh in the body. Catches by the 100-mm trawl showed a 27% reduction in all by-catch and a 28% reduction in the numbers of retained tiger flathead, compared with catches by the conventional trawl. The 100-mm trawl also showed a 48% and 47% reduction in the numbers and weights respectively of discarded tiger flathead and a 57% and 63% reduction in the numbers and weights respectively of discarded rubberlip morwong. For john dory, however, at a particular locality where large numbers occurred, the 100-mm trawl caught significantly more fish than did the conventional trawl (a mean increase in weight of 66%). There is a need to determine species-specific mesh selectivities and to study the behaviour of fish in trawls. The importance of the results for the future management and operational efficiency of trawl fisheries is discussed.

Flow Field Inside and Around a Square Fish Cage Considering Fish School Swimming Pattern

2021 ◽  
Author(s):  
Shuchuang Dong ◽  
Sang-gyu Park ◽  
Jinxin Zhou ◽  
Qiao Li ◽  
Takero Yoshida ◽  
...  
Keyword(s):  
Flow Field ◽  
Drag Force ◽  
Current Speed ◽  
Swimming Behavior ◽  
School Structure ◽  
Fish Swimming ◽  
Farmed Fish ◽  
Fish Schools ◽  
Fish School ◽  
Swimming Pattern

Abstract The interaction between fluid and fish cage with stocked fish is extremely complex, including fluid and structure, as well as fluid and fish swimming behavior. The on-current swimming pattern of fish schools was found toward the incoming flow in the previous laboratory studies, which is different from the circular swimming pattern commonly observed in the farming site. In this study, a pseudo fish school structure model (PFS) was proposed to reproduce the five circular swimming patterns of farmed yellowtail, and to investigate the influence of fish school behaviors on the flow field inside and around a model square fish cage in laboratory experiments. The results showed that the drag force acting on the square fish cage increased with the increase of the current speed for all fish school swimming patterns, but no clear difference was observed between the fish school swimming behavior patterns. Overall, the drag force of the square fish cage considering the farmed fish behavior decreased by 11.8%, compared to the drag force of the fish cage without PFS. The current speeds inside and downstream of the fish cage increased almost linearly with increasing current velocities. Compared with the case of the fish cage without PFS, the current speed inside the cage under motionless closely PFS (C0), revolving closely PFS (CR), motionless loosely PFS (L0) and revolving loosely PFS (LR) conditions changed by 10.8%, 9.4%, 65.8% and 39.7%, respectively. In addition, compared to the case of the fish cage without PFS, the current speeds under C0, CR, L0 and LR conditions decreased by 89.8%, 16.3%, 58.2%, and 31.9%, respectively, at 16.0cm downstream from the fish cage, and decreased by 69.2%, 19.4%, 62.7% and 26.3%, respectively, at 63.6cm downstream from the fish cage. Furthermore, the current speed distribution and relative horizontal turbulence intensity distribution inside and around the fish cage under different fish school swimming pattern was discussed. In the future, we will use live fish to conduct experiments to evaluate fish school models.

Variations in sex, length and age compositions of commercial catches of Platycephalus fuscus (Pisces : Platycephalidae) in New South Wales, Australia

2002 ◽  
Vol 53 (7) ◽  
pp. 1091 ◽  
Author(s):  
C. A. Gray ◽  
V. J. Gale ◽  
S. L. Stringfellow ◽  
L. P. Raines
Keyword(s):  
Average Length ◽  
New South ◽  
New South Wales ◽  
Total Mortality ◽  
Mesh Size ◽  
Growth Zone ◽  
Male Fish ◽  
Age Composition ◽  
South Wales ◽  
By Catch

Commercial landings of dusky flathead (Platycephalus fuscus) from four estuaries in New South Wales (NSW), Australia, were sampled for data on sex, length and age composition between February and July each year for 2–3 years between 1995 and 1997. Landings primarily contained female fish, ranging from 55% to 93% by number for different estuaries. Flathead sampled in commercial catches ranged from 30 cm to 96 cm total length (TL), but the majority were 33–50 cm TL. Fish >40 cm TL were primarily female and male fish >45 cm TL were uncommon. The length composition of catches differed between gillnets of different mesh sizes, with the average length of fish being least in the smallest allowed mesh size of 70 mm. Fish were aged by otolith interpretation and the analysis of marginal increments indicated that one opaque and one translucent growth zone was formed each year; the opaque zone being deposited in June–August (winter) and first observed in September–October (spring). Commercial landings included fish aged 2–11+ years, but fish aged 2–4+ years dominated landings in all estuaries. The total mortality of dusky flathead in each estuary was estimated by catch curve analysis and was relatively high, ranging from 0.45 to 1.64. The data indicate that dusky flathead may be heavily exploited in NSW.

Experimental Study on the Effect of Reynolds Number Variation on Drag Force for Various Cut Angle on D-Type Cylinders

2014 ◽  
Vol 493 ◽  
pp. 140-144
Author(s):  
Astu Pudjanarsa ◽  
Ardian Ardawalika
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Drag Force ◽  
Free Stream ◽  
Force Balance ◽  
Stream Velocity ◽  
Turning Angle ◽  
Subsonic Wind Tunnel ◽  
Minimum Drag ◽  
Number Variation

Experimental study on the effect of Reynolds number variation on drag force for various cut angles on D-type cylinders was performed. Five different cut angles on different cylinders were applied including: 35o, 45o, 53o, 60o, and 65o. The free stream velocity was varied so the Reynolds number also varied.The experiment was carried out at a subsonic wind tunnel. Drag force for a cut D-type cylinder (for example 35o) was measured using a force balance and wind speed was varied so that corresponding Reynolds number of 2.4×104÷5.3×104 were achieved. Wind turning angle was kept at 0o (without turning angle). This experiment repeated for other D-type cylinders.Experiment results show that, for all D-type cylinders, drag force decreased as the Reynolds number increased, then it was increased after attain minimum drag force. For all D-type cylinders and all variations of Reynolds number the drag minimum is attained at cut angle of 53o. This value is appropriate with previous experiment results.

scholarly journals Modelling of Drag Force Reduction for a Waterjet Propulsion System

2021 ◽  
Vol 58 (5) ◽  
pp. 3-14
Author(s):  
M. Cerpinska ◽  
M. Irbe ◽  
A. Pupurs ◽  
K. Burbeckis
Keyword(s):  
Drag Coefficient ◽  
Drag Force ◽  
Velocity Ratio ◽  
The Body ◽  
Inlet Velocity ◽  
Minimum Drag ◽  
Simulation Results ◽  
Force Reduction ◽  
Design Options ◽  
Coefficient Reduction

Abstract The paper provides simulation results for SUP (Stand Up Paddle) board appendage resistance. Additional propulsion is added to the SUP board. It is equipped with a waterjet. The waterjet is attached to the board rudder. This increases the drag coefficient for rudder five times. To reduce the drag variable, design options for the waterjet duct were proposed. The simulation tests were performed using SolidWorks Flow software using two types of simulations, namely, the pressure on the body and the flow around the body. The objective was to streamline the bluff duct of the waterjet and thus to create the appendage design with minimum drag force from fluid flow and possibly greater Inlet Velocity Ratio. Calculations showed that rounding-off the edges of waterjet duct resulted in 35 % of drag coefficient reduction, while further streamlining reduced it by additional 10 %.

scholarly journals STATUS KEBERLANJUTAN PERIKANAN BAGAN PERAHU BERBASIS BIO-EKONOMI DI DESA TONIKU KABUPATEN HALMAHERA BARAT

2019 ◽  
Vol 11 (1) ◽  
pp. 181-190
Author(s):  
Irwan Abdu Kadir ◽  
Adi Noman Susanto ◽  
Amirul Karman ◽  
Iinpuspita Ode Ane
Keyword(s):  
Fish Larvae ◽  
Economic Value ◽  
Survey Method ◽  
Fishing Gear ◽  
Economic Aspects ◽  
Study Objective ◽  
Study Results ◽  
Fish Catch ◽  
Business Profit ◽  
By Catch

ABSTRAKNelayan di Desa Toniku Kabupaten Halmahera Barat, awalnya menggunakan bagan perahu untuk menangkap ikan teri Stolephorus sp. sebagai umpan perikanan pole and line, akan tetapi pada saat ini banyak tertangkap selain teri yaitu juvenil dan larva ikan, ini permasalahan yang perlu dikaji komposisi tangkapan dari bagan perahu. Tujuan penelitian  adalah  menganalisis komposisi tangkapan, by-cacth, discard, dan aspek ekonomi. Penelitian  dilaksanakan di perairan desa Toniku Kabupaten Halmahera Barat, dari tanggal 1 sampai 9 Juni 2018. Metode penelitian adalah metode survei. Obyek penelitian yaitu ikan hasil tangkapan bagan perahu. Hasil penelitian menunjukkan bahwa tangkapan bagan perahu didominasi oleh ikan target tangkap, yaitu; ikan teri (Stolephorus sp) sebesar 86,295%, tangkapan sampingan  12,335% dan tangkapan yang dibuang 1,370%. Tangkapan sampingan didominasi ikan  peperek (Leiognatus sp) yaitu 5,575%. Nilai keuntungan Usaha bagan perahu sebesar Rp 93.047.200,00/tahun dengan B/C ratio 2,96. Berdasarkan perbandingan antara target tangkap dengan by-catch dan discard, bagan perahu di Desa Toniku Kabupaten Halmahera Barat dikategorikan alat tangkap ramah lingkungan dan secara finansial menguntungkan dan layak dikembangkan (berkelanjutan). Walaupun discard rate pada bagan perahu rendah namun usaha-usaha untuk meminimumkan tetap perlu dilakukan. Salah satu usaha yang bisa dilakukan adalah sortir, dan hasil tangkapan yang tidak memiliki nilai ekonomis dibuang ke laut dalam keadaan masih hidup. ABSTRACTFishermen in Toniku Village, West Halmahera Regency, initially used a boat lift net to catch anchovy Stolephorus sp. As bait for pole and line fisheries, but at this time many were caught besides anchovy, namely juvenile and fish larvae, these are problems that need to be studied from the boat lift net. The study objective was to analyze the composition of catchs, by-catch, discard, and economic aspects. The research was carried out in the waters of Toniku village, West Halmahera Regency, from June 1 to 9, 2018. The study method is the survey method. The object of the research is the fish catch by the boat lift net. The study results show the catch of the boat's lift net was dominated by main catch, namely; anchovy (Stolephorus sp) is 86.295%, by-catch 12.335% and discard 1.370%. The bay-catch  is dominated by peperek (Leiognatus sp) which is 5.575%. Value of the boat lift net business profit of Rp. 93,047,200.00/year with B/C ratio 2.96. Based on the comparison between catch targets and by-catch and discard, the boat lift net in Toniku Village, West Halmahera Regency is categorized as environmentally friendly and financially profitable and feasible (sustainable) fishing gear. Although the discard rate on the boat chart is low, efforts to minimize it still need to be done. One effort that can be done is sorting, and catches that have no economic value are dumped into the sea while still alive.

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