Minimum Mesh Size Research Articles

Codend selectivity in the East China Sea of a trawl net with the legal minimum mesh size

Selectivity curves were obtained for 22 species of fish and squid from stock assessment research data for the East China Sea between 2001 and 2011, conducted using a cover net attached to the codend of a trawl net (Seikai National Fisheries Research Institute SS-RI-type trawl net). The trawl net codend was made of diamond mesh net with a legal minimum mesh opening size of 54 mm (mesh length of 66 mm). A cover net with a mesh opening of 18 mm (or 10.3 mm depending on the research year) was attached to the codend. For each of the 20 fish species and two squid species, we pooled data of hauls where body size for the whole catch was measured without subsampling to obtain the body size compositions of fish caught in both the codend and the cover net. The maximum likelihood method was performed for estimation of parameters in the logistic curve equation representing the codend selection curve. For 18 fish species (excluding Trichiurus japonicus and Muraenesox cinereus), we examined the relationship of the obtained selection parameters [length at 50% retention (l50) and selection range (SR) (= l75–l25)] to fish body shape. We demonstrated that, in fish species with a smaller ratio of body height/width to body size (i.e., more slender body type), there was a tendency for larger l50 and SR. Furthermore, by comparing the l50 of each fish species with reproductive parameters such as minimum length at maturity, we examined the sustainability of the resources based on the minimum mesh size regulation.

Quantifying the morphology of key species caught in the southern Brazilian penaeid trawl fishery as a precursor to improving selection

Penaeid trawls are poorly selective fishing gears; contributing towards approximately 27% of global marine fisheries discards. Various options are available for mitigating penaeid-trawl bycatch, including gear modifications such as ‘bycatch reduction devices’ (BRDs) or codend mesh-size regulations. A precursor to developing modifications is information about the key target and bycatch species in terms of their sizes and morphology. Here we describe the relationships between these characteristics for the southern Brazilian industrial penaeid-trawl fishery within a broader objective of proposing more selective trawl configurations. Catches were sampled during 37 tows. Fifty-two species were caught, including two loggerhead turtles, Caretta caretta , one green turtle, Chelonia mydas , as well as 61 individuals of seven ray species classified as Endangered or Critically Endangered. One penaeid ( Pleoticus muelleri ) and 11 teleosts were assessed for various morphological relationships. The data demonstrated that both the existing conventionally used 26 mm (stretched mesh opening; SMO) mesh and a legislated size of 30 mm SMO are too small. Using morphological relationships, we propose testing a minimum diamond-shaped mesh size of at least 35 mm and a square-mesh window in the top of the codend comprising at least 48 mm mesh. Such a configuration would probably retain penaeids and larger teleosts, but allow many small teleosts to escape. Anteriorly located grids are also required to reduce the bycatch of charismatic species like turtles and rays. Wide-scale use of such BRDs should considerably reduce bycatches and the ancillary impacts of regional penaeid-trawl fisheries.

Size selectivity of combined square and diamond mesh codends of shrimp beam trawl for banded scad Caranx ( Atule ) kalla in the northern South China Sea

The shrimp beam trawl fishery in the northern South China Sea is characterized by high by-catch and poor selectivity problems. Among by-catch species, banded scad ( Caranx ( Atule ) kalla ) is economically the most important one. The aim of this study is to improve the selective properties of codends for banded scad. Size selectivity of 2 traditional diamond mesh codends, with mesh size 25 and 30 mm (defined as D25 and D30, respectively), and 4 new combined square and diamond mesh codends, with 25 mm square-mesh and 25 mm diamond-mesh (S25+D25), 30 mm square-mesh and 25 mm diamondmesh (S30+D25), 35 mm square-mesh and 25 mm diamond-mesh (S35+D25), and 35 mm square-mesh and 18 mm diamond-mesh (S35+D18), were tested for banded scad in shrimp beam trawl fishery of the South China Sea. A total of 54 valid hauls were finished using the covered codend method, and 5750 banded scad were caught. Selective parameters were obtained using the logistic equation with the maximum likelihood method, by incorporating the between-haul variation. The results show that the present minimum mesh size for shrimp beam trawl in the South China Sea, 25-mm diamond mesh size, is insufficient to release immature banded scad. The S35+D25 codend is proved to be the most effective codend to release immature banded scad, and its 50% retention length ( L50 ) is larger than the minimum landing size (MLS=63.5 mm) of banded scad. However, the 95% confidence intervals of L50 overlap among the three combined mesh codends, the S25+D25, S30+D25 and S35+D25 codend. For a sustainable exploitation of banded scad, larger mesh sizes are suggested to be investigated for the combined mesh codends.

Numerical investigation of the fluid lag during hydraulic fracturing

PurposeThe purpose of this paper is to systematically investigate the fluid lag phenomena and its influence in the hydraulic fracturing process, including all stages of fluid-lag evolution, the transition between different stages and their coupling with dynamic fracture propagation under common conditions.Design/methodology/approachA plane 2D model is developed to simulate the complex evolution of fluid lag during the propagation of a hydraulic fracture driven by an impressible Newtonian fluid. Based on the finite element method, a fully implicit solution scheme is proposed to solve the strongly coupled rock deformation, fluid flow and fracture propagation. Using the proposed model, comprehensive parametric studies are performed to examine the evolution of fluid lag in various geological and operational conditions.FindingsThe numerical simulations predict that the lag ratio is around 5% or even lower at the beginning stage of hydraulic fracture under practical geological conditions. With the fracture propagation, the lag ratio keeps decreasing and can be ignored in the late stage of hydraulic fracturing for typical parameter combinations. On the numerical aspect, whether the fluid lag can be ignored depends not only on the lag ratio but also on the minimum mesh size used for fluid flow. In addition, an overall mixed-mode fracture propagation factor is proposed to describe the relationship between diverse parameters and fracture curvature.Research limitations/implicationsIn this study, relatively simple physical models such as linear elasticity for solid, Newtonian model for fluid and linear elasticity fracture mechanics for fracture are used. The current model does not account for such effects like leak off, poroelasticity and softening of rock formations, which may also visibly affect the fluid lag depending on specific reservoir conditions.Originality/valueThis study helps to understand the effect of fluid lag during hydraulic fracturing processes and provides numerical experience in dealing with the fluid lag with finite element simulation.

Lüferin (Pomatomus saltatrix) morfolojisiyle galsama ağı seçiciliğinin tahmini

The dataset of the study consists of total length, fork length, head girth, maximum girth and weight measurements of 136 bluefish. The relationship between the total length and fork length of the product was TL=1.1348×FL - 0.8184; the relationship between the total length and weight was W =0.0103× L 2.97 . The relationships between the total length and head girth and between the total length and maximum girth of the sample were linear: the relationship of the total length and head girth was G gill =0.5092×TL - 0.0874; the relationship of the total length and maximum girth was G max =0.5989×TL - 0.8540. The statistical relationship between length and girth was used to obtain a theoretical gillnet selectivity equation for the species. In conclusion, a relationship of S ( l )=Φ[( C - G gill )/0.4952]×[1 - Φ(( C - G max )/0.4255)] was determined between the stretched size of the mesh used in bluefish fishing and the catch rate. Using this equation, and considering the legal length and length at first maturity, the minimum mesh size of the gillnet for sustainable fishery was determined.

Bioeconomic assessment of a change in fishing gear selectivity: the case of a single-species fleet affected by the landing obligation

The European Union Common Fisheries Policy has established a discard ban, which states that fish below a reference size cannot be sold directly for human consumption. In a fishing effort-regulated fishery, the discard ban can result in extra handling, storing and landing costs. In an output-regulated fishery, this policy might also limit the effort levels as all the catches count against the quota. In both cases, this regulation can reduce the economic performance of the companies, even in single-species fisheries. A possible solution is to increase the mesh size, thus retaining fewer small individuals. To study this option, a bioeconomic simulation of a change in the gear selectivity from 100- to 120-mm minimum mesh size (MMS) was performed. The results show that the private perspective (profits) does not change. Furthermore, due to the lower retention of 120 mm MMS, the efficiency of a fishing day was reduced by 5% and 2.5%, from the point of view of capital and labour productivity, respectively. In contrast, gross revenues increased by 1.5% and crew compensation by 2%. Given a societal benefit of this change in the mesh size, this gain could be re-distributed to provide an incentive for selectivity improvements.

Fisheries Management in the Black Sea—Pros and Cons

In Black Sea the term ”management” usually is interpreted as series of regulatory measures introduction in the fishery practice with no doubt, positive influence on the general condition of marine living resources. On the other hand, similar restrictions could not lead conceptually to the “management policy” if they are not systematized with clearly formulated aims and prerogatives. In the presence of introduced “closed area”, ”closed season”, ”minimum mesh size” and other regulations, altogether all of these measures could not serve as restrictions over the yield capacity, i.e. could not influence the fishing effort. The main priority in such a conception is a precautionary approach and responsible fishery practice in force. It could “work” properly with quota principle implementation, together with more effective system control. It is hard for the any single country to follow these regulations and it is harder for all Black Sea countries to do so, because they are exploiting resources from shared fish stocks. In order to have an effective management on these stocks, joint stock assessments are needed. On this basis, the allocation of the catches for the separate Black Sea country could be established. Unfortunately, due to the different reasons, for the time being this is impossible. Hence, it could be assumed that management of the marine living resources shall be fulfilled in its incomplete form, under the national jurisdiction prescript, as they are.

Trammel net size-selectivity for Hipposcarus harid (Forsskål, 1775) and Lethrinus harak (Forsskål, 1775) in coral reef fisheries of Jeddah, Saudi Arabia

The present study estimated the size-selectivity of Hipposcarus harid and Lethrinus harak caught in monofilament trammel nets of 50, 56, and 62mm inner-panel mesh sizes. Fishing was carried out in the coral reef fisheries of Jeddah during the period from June 2013 to March 2014. The selectivity parameters were calculated using the SELECT method implemented in Pasgear 2 software. The normal location, normal scale, log-normal, gamma and bi-modal selectivity models were fitted to the data to estimate the selectivity curves. Results indicated that the log-normal model provided the best fit based on the lowest deviance value. Modal lengths estimated from the log-normal selectivity curves are: 19.73, 22.10, and 24.46cm for H. harid, 18.41, 20.62, and 22.83cm for L. harak caught with 50, 56 and 62mm inner-panel mesh sizes, respectively. The length–girth relationship was estimated and described by the linear equation: G=0.480+0.70L (r2=0.95) for H. harid, and G=0.73L−0.65 (r2=0.96) for L. harak. For proper management of H. harid and L. harak, the minimum inner-panel mesh size should be 62mm to catch fish sizes larger than the length at maturity for both species.

ANALYSIS OF DEBRIS FLOW DISASTER DUE TO HEAVY RAIN BY X-BAND MP RADAR DATA

On August 20 of 2014, Hiroshima City (Japan) was struck by local heavy rain from an autumnal rain front. The resultant debris flow disaster claimed 75 victims and destroyed many buildings. From 1:30 am to 4:30 am on August 20, the accumulated rainfall in Hiroshima City exceeded 200 mm. Serious damage occurred in the Asakita and Asaminami wards of Hiroshima City. As a disaster prevention measure, local heavy rain (localized torrential rains) is usually observed by the Automated Meteorological Data Acquisition System (AMeDAS) operated by the Japan Meteorological Agency (JMA) and by the C-band radar operated by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) of Japan, with spatial resolutions of 2.5 km and 1 km, respectively. The new X-band MP radar system enables more detailed rainfall observations than the C-band radar. In fact, this radar can observe local rainfall throughout Japan in near-real time over a minimum mesh size of 250 m. A fine-scale accumulated rainfall monitoring system is crucial for disaster prevention, and potential disasters can be alerted by the hazard levels of the accumulated rainfall.

ANALYSIS OF DEBRIS FLOW DISASTER DUE TO HEAVY RAIN BY X-BAND MP RADAR DATA

Abstract. On August 20 of 2014, Hiroshima City (Japan) was struck by local heavy rain from an autumnal rain front. The resultant debris flow disaster claimed 75 victims and destroyed many buildings. From 1:30 am to 4:30 am on August 20, the accumulated rainfall in Hiroshima City exceeded 200 mm. Serious damage occurred in the Asakita and Asaminami wards of Hiroshima City. As a disaster prevention measure, local heavy rain (localized torrential rains) is usually observed by the Automated Meteorological Data Acquisition System (AMeDAS) operated by the Japan Meteorological Agency (JMA) and by the C-band radar operated by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) of Japan, with spatial resolutions of 2.5 km and 1 km, respectively. The new X-band MP radar system enables more detailed rainfall observations than the C-band radar. In fact, this radar can observe local rainfall throughout Japan in near-real time over a minimum mesh size of 250 m. A fine-scale accumulated rainfall monitoring system is crucial for disaster prevention, and potential disasters can be alerted by the hazard levels of the accumulated rainfall.

North Spanish fisheries: discards, causes and reduction measures

North Spanish fisheries: discards, causes and reduction measures

Finite Element Analysis of Porous Medical Grade Cobalt Chromium Alloy Structures Produced by Selective Laser Melting

The recent introduction of selective laser melting (SLM) for the processing of medical grade cobalt chromium (CoCr) alloy has led to a complex shape fabrication of porous custom CoCr alloy implants with controlled porosity to meet the requirements of the anatomy and functions at the region of implantation. This paper discusses finite element (FE) analysis and mechanical characterization of porous medical grade CoCr alloy in cubical structures with volume based porosity ranging between 60% and 80% produced using SLM rapid manufacturing process. Analysis by FE is considered beneficial to predict the effective mechanical properties of the porous structures manufactured by SLM due to minimization of the need for expensive and time consuming physical testing. Cellular structures modelling for fabrication with Direct Metal Laser Sintering machine were designed to vary between 60% and 80% to study the effect of structural variation on mechanical properties of the cellular porous structure. ANSYS 14.0 FE modelling software was used to predict the effective elastic modulus of the samples and comparisons were made with the experimental data. FE results show that with the material properties in the functions of porosities, minimum mesh size of 0.2 mm for triangular shape mesh and boundary as well as load conditions as applied in this study, agreement in equivalent stress, strain and deformation with the experimental results can be achieved to some extent. The technique for FE in this study can be used to investigate stress distribution in three dimensional model of real bone.

Minimum mesh size of bird net entered by Eurasian Tree Sparrow, Passer montanus and digging behaviour

Minimum mesh size of bird net entered by Eurasian Tree Sparrow, Passer montanus and digging behaviour

The effect of mesh division of a volume source on calculated radiation flux distribution

A sensitivity analysis of a point kernel code was performed to investigate the effect of mesh division of a volume source on the radiation flux at points of interest. The QAD-CGGP, known as a representative point kernel code, was employed for a series of calculations and these calculation results compared with the reference data obtained from the MCNP5-1.60 code. The spherical volume source widely used in radiation shielding was also considered in this work and the mesh division along the radius was performed in two ways (regular and irregular). In addition, an approximate equation was defined to correct the significant error that occurs as an outcome of the point source assumption. As a result, in the case of a regular mesh division, a minimum mesh size of 1 cm is required to produce accurate results in comparison to the MCNP ones, while in the other instance, a half-level mesh division is sufficient to obtain the same result from the standpoint of the level of accuracy. In addition, by introducing the approximate equation presented in this paper, a significant error resulting from the point source assumption is exponentially reduced from a maximum of ~30% to a maximum of ~11%. Therefore, it is to be expected that the appropriate level of mesh division is required so as to increase the accuracy of the calculation using a point kernel method.

Tailoring codend mesh size to improve the size selectivity of undifferentiated trawl species

AbstractTiger flathead, Neoplatycephalus richardsoni (Castelnau), and sand flathead, Platycephalus bassensis Cuvier, are undifferentiated and managed with a common legal minimum length (LML). The Commonwealth Trawl Sector (CTS) and the Tasmanian Danish‐seine fishery (TDSF) use a minimum codend mesh sizes of 90 and 70 mm, respectively. The codend mesh size should be tailored to the LML, which is based on the length of first maturity of females (M50). This study found the length–girth relationship of N. richardsoni and P. bassensis was not significantly different. Using the covered codend method, these two species had 50% retention lengths (L50) of 294 ± 2 and 307 ± 3 mm, in 70‐mm and 90‐mm codends, respectively. L50 estimates for mesh sizes from this study and others produced a curvilinear relationship: y = 120 ln(x) − 214, with an r2 of 0.8504. The size at maturity (M50) for female N. richardsoni was 337 mm, which is larger than the estimate for female P. bassensis (247 mm). There is a mismatch between the estimates of L50, the estimates of M50 and the LMLs in each fishery, leading to suboptimal exploitation of female Platycephalus. The model produced in this paper recommends a codend mesh size of 98 mm for both fisheries to exploit Platycephalus species sustainably.

Preliminary evaluation of landings and discards of the Turkish bottom trawl fishery in the northeastern Aegean Sea (eastern Mediterranean)

Summary: This short-term study on commercial discards was carried out in fishing grounds around Gokceada Island in the northeastern Aegean Sea, a geographic area where fisheries information is rather limited. A total of 28 bottom trawls were performed between 70 and 410 m depth from December 2009 to February 2010. All the samples were collected on board a commercial trawler under commercial fishing conditions. A total of 3143 kg of biomass was caught in 28 valid hauls. Landings accounted for about 67% of the total catch while the remaining 33% was discarded. Fish species comprised 85% of the total catch and their composition could be divided into four main groups related to depth: shallow shelf (70 to 88 m), deep shelf (155 to 180 m), shelf break (196 to 276 m), and upper slope (307 to 410 m). Fish dominated the abundance and biomass of both landings and discards in all bathymetric strata. Echinoderms also accounted for a large proportion of the discards. Mean total catches varied between 78.4 kg/h on the shallow shelf and 38.1 kg/h on the shelf break with no differences in the landing biomass between groups, but with slightly higher discards over the shallow shelf. Taking into account the preliminary nature of the findings, based on a short-term analysis, the minimum mesh size and minimum landing size currently applied in the Turkish bottom trawl fishery are not sufficient to reduce discards and to protect juveniles of commercially important species in the northeastern Aegean Sea.

Effect of Mesh Size on Calculation of Strain Non-uniformity Index in Drawn Sheet Metal Parts

The spatial variation of the true major, minor and thickness strains is the combined outcome of a number of material, tool, geometric and deformation variables (many of which cannot be measured) and their complex interactions over various levels.When one calculates the strain nonuniformity index from an FEM simulation, the mesh size can be expected to influence the value of the strain nonuniformity index leading to a wrong prediction of failure. This is similar to the effect of grid circle size and circle spacing in experimentally measured strain distribution. The present paper attempts to bring out a minimum mesh size for the critical strain nonuniformity index to remain unaffected by the meshing effects. This will enable the user to set an adequate level of mesh refinement during adaptive meshing without an excessive increase in the computational cost. Comparatively, the ‘constraint factor’, which denotes the ratio of the difference between the minor strains at the peak and the pole to that between the major strains at these two locations, is likely to be much less affected by the mesh size. strain nonuniformity index reaching a critical value is accompanied by the constraint factor moving towards zero.

Discrete Equation Method (DEM) for the simulation of viscous, compressible, two-phase flows

A numerical approximation of a five equations model for the simulation of two-phase flows, including viscous effects is illustrated. A DEM approach is developed obtaining a clear formulation of viscous fluxes and an accurate resolution method for all terms. Starting from a system composed by the Navier–Stokes equations for each phase, a final 1D semi-discrete equation for the discretization of pressure and velocity equilibrium model is obtained.First, the influence of viscous terms is studied comparing viscous and inviscid solutions in two-phase configurations. This analysis allows to identify the thermodynamic quantities, such as pressure, velocity, phase densities and volume fraction that are influenced by the viscous effects. Then, several gas/liquid mixtures, obtained modifying the gas/liquid viscosity ratio, are compared in order to study the influence of viscous effects in terms of phase volume fraction, density and entropy. Finally, the influence of mesh on the viscosity, in terms of minimum mesh size needed to evaluate the viscous effects in the simulation, is shown.

An overview of marine fisheries management in China

China is the world's largest country in terms of fish production, yet its fisheries management is comparatively unknown outside the country. This article gives an overview of the current management system and highlights some of its challenges. In the past 30 years, the Department of Fishery Administration has formulated and organized a series of conservation and management regimes and measures. The most important tools are minimum mesh size regulation and a range of input control measures, including seasonal closures and attempts to control fishing capacity through licensing and limiting total engine power. However, fisheries output is only controlled through a nation-wide total catch limit. Certain progress has been achieved, but there are still problems as the resource situation is poor. While the existing measures could, in principle, improve sustainability, their enforcement is insufficient, and they do not limit fishing effort in a way that would allow recovery.

Medidas de conservación y ordenación pesquera del jurel Trachurus murphyien el Perú

The Peruvian fisheries exploit renewable natural resources and as such are regulated by a legal framework aiming at ensuring their conservation and sustainable use. The General Fisheries Act, DL N°. 25977, points out that fisheries management systems shall be established for each type of fishery taking into account to the state of exploitation of the fishery resources, reconciling the principles of sustainability and long-term conservation with those aiming at the attainment of the maximum possible economic and social benefits. According to the provisions of the Fisheries Management Regulations approved by SD N°. 011-2007-PRODUCE, the management of the Jack mackerel Trachurus murphyifisheries includes among others, a fishing access regime that regulates the fleet size and the allocation of fishing licenses, which can only be granted to vessels fishing only for direct human consumption. The obligation to allocate the resources sardine Sardinops sagax, Jack mackerel T. murphyi, and mackerel Scomber japonicus, for direct human consumption has been in force since September 2002, following the ruling established by SD N°. 001-2002-PRODUCE. Other measures currently in force include those establish a minimum mesh size, the ban to catch or land specimens under 31 cm total length limit, the opening and closing of the fishing seasons, and catch limits or annual quotas. These provisions are supplemented by measures for monitoring, control and surveillance, and for the effective conservation and sustainable use of the fishery resources.