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Compartmental shielding, using methods such as the conductive encapsulation of flexible polymer fibers, provides electrical pathways that are effective for electromagnetic interference (EMI) shielding in textile-based EMI shields. However, controlling the skin depth with electrically insulating polymer constituents remains challenging, particularly by requiring the high electrical conductivity of the encapsulants on the surface. Here, we demonstrate that the highly conductive single-walled carbon nanotube (SWCNT) polyelectrolytes provide a certain level of electrical conductivity (∼106 S/m) with effective percolation that reduces the skin depth to approximately 3 μm. This experimental skin depth was well-matched with the theoretical value of the skin depth. Sufficient charge accumulation in the SWCNT encapsulants with a hierarchical structure indicates the remarkable conductive features of the SWCNT polyelectrolytes and successfully demonstrates absorption-dominant EMI shielding. The macroscopic square mesh consisted of core/shell aramid/SWCNT fibers, exhibiting an ordered structure across multiple length scales, a modified hierarchy, and a superior EMI shielding effectiveness (SE), particularly in absorption. In particular, an EMI SE (i.e., 32 dB) of approximately 99.9% was achieved using a square mesh with an aperture width of 3 mm. The square meshes demonstrated excellent flexibility, thermal stability (Td > 500 °C), and mechanical robustness (σ = 2.26 ± 0.16 GPa, E = 79.0 ± 1.8 GPa, and ε = 2.99 ± 0.09%). [ABSTRACT FROM AUTHOR]

The size selectivity and catch pattern of Trichiurus lepturus in 40 mm diamond and square mesh codends were investigated in this study. A 34 m high opening trawl was used, which is a common design used by fishermen operating along the northwest coast of India, and the cover codend method was employed to determine codend selectivity. Along with the changes in the length at 50% retention rate for Trichiurus lepturus with the usage of the square and diamond mesh codends, indicators to understand the exploitation pattern of this species in the fishery were assessed based on the total number of individuals and on total weight of the catch. The mean selection length increased and discard fraction is reduced when 40 mm square mesh codends are used in place of diamond meshes, however, it is observed that individuals at commercial length are also lost. The results demonstrate that mandatory use of legal mesh sizes alone will be insufficient to aid in the sustainable harvest of this species, given its estimated length at first sexual maturity of 61.2 cm. This is the first study to compare the size selection of this species in 40 mm diamond and square mesh codends along Northwest coast of India. Results of the study will help as a baseline for gear-based regulations in the region.

When analyzing structures, there are several different methods that are used. The method most often used in analysis is the finite element method. The finite element method was also used in the elaboration of the problem herein, and it is related to displacement in plate structures. Numerical models will be approximated by finite triangular elements in the CYPE program and by finite square elements in the TOWER 3D Model Builder program. In the end, a comparison will be made of the results and of the influence of the type and density of the finite element mesh as well as the quality of the concrete on the result of the analysis.

The size selectivity and catch pattern of Trichiurus lepturus in 40 mm diamond and square mesh codends were investigated in this study. A 34 m high opening trawl was used, which is a common design used by fishermen operating along the northwest coast of India, and the cover codend method was employed to determine codend selectivity. Along with the changes in the length at 50% retention rate for Trichiurus lepturus with the usage of the square and diamond mesh codends, indicators to understand the exploitation pattern of this species in the fishery were assessed based on the total number of individuals and on total weight of the catch. The mean selection length increased and discard fraction is reduced when 40 mm square mesh codends are used in place of diamond meshes, however, it is observed that individuals at commercial length are also lost. The results demonstrate that mandatory use of legal mesh sizes alone will be insufficient to aid in the sustainable harvest of this species, given its estimated length at first sexual maturity of 61.2 cm. This is the first study to compare the size selection of this species in 40 mm diamond and square mesh codends along Northwest coast of India. Results of the study will help as a baseline for gear-based regulations in the region. [ABSTRACT FROM AUTHOR]

When analyzing structures, there are several different methods that are used. The method most often used in analysis is the finite element method. The finite element method was also used in the elaboration of the problem herein, and it is related to displacement in plate structures. Numerical models will be approximated by finite triangular elements in the CYPE program and by finite square elements in the TOWER 3D Model Builder program. In the end, a comparison will be made of the results and of the influence of the type and density of the finite element mesh as well as the quality of the concrete on the result of the analysis. [ABSTRACT FROM AUTHOR]

Commercial bycatch species and their exploitation pattern in the Mediterranean trawl fishery are little studied. The present work examines the overall size-selection pattern, both regarding the trawl in the sea and the fisher onboard the vessel, for seven commercial bycatch species using different codends. The applied selection model predicted the escape, discard, and landing probability for each species simultaneously, a useful method for providing information important for fisheries management under the ecosystem approach. Among the studied codends, the 40-mm diamond mesh codend, still in use in non-EU Mediterranean fleets, was found unsuitable for the stocks in all cases. The 40-mm square mesh codend (40S) was found appropriate for blue whiting (Micromesistius poutassou), comber (Serranus cabrilla), and bogue (Boops boops) sustainability. The 50-mm diamond mesh codend (50D) was more suitable than the square mesh codend only for the spotted flounder (Citharus linguatula). Both the 40S and the 50D codends were appropriate for picarel (Spicara smaris), whereas none ensured sustainable exploitation for the blackbelly rosefish (Helicolenus dactylopterus), and the streaked gurnard (Chelidonichthys lastoviza). The results are discussed in relation to juvenile protection, discard mitigation, and fisher selection behaviour, important factors for the sustainability of stocks and fisheries in the Common Fishery Policy for the Mediterranean Sea. [ABSTRACT FROM AUTHOR]

To explore the effect of the shape and size of the stow net cod-end mesh on the selectivity of Larimichthys polyactis, three different mesh openings were adopted as 30 mm, 40 mm, 50 mm for diamond-mesh cod-end, and 20 mm, 30 mm, 40 mm for square-mesh cod-end in this study, respectively. 12 at-sea trials were carried out in the Haizhou Bay of the Yellow Sea in autumn 2020, using the covered cod-end method. The Logistic selectivity model was applied in the study, based on the analysis of the composition of the catch and the escape rate of juveniles. The effects of mesh shape and mesh size on the selectivity of Larimichthys polyactis were analyzed. The results showed that:63 kinds of fish were caught in the experiment, the body length of Larimichthys polyactis ranged from 80 mm to 134 mm, and the average body length was 106 mm. The proportion of the catch in the diamond mesh and square mesh to the total catch was 41. 45% and 36. 83%, respectively. Under the same mesh size, the release effect of juvenile Larimichthys polyactis with square mesh is better than that of diamond mesh. When the mesh size is 40 mm, the number and mass escape rate of square mesh is 34. 53% and 34. 39 higher than those of diamond mesh, respectively. The 50% selection body length (L50) of the 30 mm and 40 mm square mesh was 5. 93% and 18. 84% higher than the corresponding diamond meshes. The juvenile proportion of Larimichthys polyactis is very high, more than 90%, and almost all of them are juvenile fish. Based on the above test results, considering the resource status and production efficiency of Larimichthys polyactis in Haizhou Bay, it is recommended to expand the mesh size of the cod-end net for fishing Larimichthys polyactis from the currently specified diamond mesh of 35 mm to 50 mm of diamond mesh, or square mesh with 40 mm, to achieve the purpose of effectively protecting the juvenile resources of Larimichthys polyactis. [ABSTRACT FROM AUTHOR]

In order to improve the capacity of bottom trawl fishing gear to reduce catches of young fish and discards in a highly exploited demersal trawl fisheries in the Arabian sea, the size-selection performance of a 35 mm square-mesh codend and two sorting grids with 20 and 15 mm bar spacing was assessed. Similarly, the 40 mm Diamond meshes in the trawl codend also assessed in the same region to know the catch composition of commercial fish species. Alternate hauls were used to assess the selectivity of 35 mm square-mesh codend with 40 mm diamond mesh along with cover codend to know the escaped fishes. Selectivity of sorting grids was assessed using a double codend in which the fishes that escaped through the grid were captured in the lower codend while other fishes were guided into the upper codend. The mean selection length (L50) for wt. of prawns, Wt. of total discarding by-catch, wt. of discarding non commercial by-catch, wt. of retained by catch, wt. Pink perch, wt. of Ribbon fish, wt. of Lizard fish, wt. of Anchovy, wt. of Bull’s eye fish, wt. of Cuttlefish and wt. of Mackerel were found in both the codend used during fishing were noted. It has also been observed that commercial fishes caught more in case of 35 mm Square mesh codend than that of 40 mm diamond mesh used with grids in the codend trawl net. [ABSTRACT FROM AUTHOR]

In this study, the selectivities of commercial 44 mm nominal polyethylene (PE) diamond mesh (PE44DM) and square mesh (PE44SM) codends for red mullet Mullus barbatus fisheries in Antalya Bay, Eastern Mediterranean, were compared and modelled. For this purpose, a conventional bottom trawl of 600 meshes was operated onboard R/V “Akdeniz Su” during night time at 25-50 m depths for a total of 21 hauls. Data were collected using the covered codend technique, and analysed using a logistic equation with maximum likelihood by SELNET software. The PE44DM codend had a higher catch rate (89.6%) and 32.5% of M. barbatus were below the minimum landing size whereas catch rates decreased to 42.1% and 9.9%, respectively, in the PE44SM codend. Changing from the diamond mesh to square mesh codend increased the mean L50 and SA values from 8.2 to 13.2 cm and from 2.11 to 2.87 cm, respectively. Both L50 and SA values obtained in the present study show a statistically significant increase (no overlap in 95% confidence limits) with a change in the same mesh size codends from diamond to square for M. barbatus. The use of the PE44SM codend resulted in a significant improvement in the selectivity of M. barbatus compared to the currently used PE44DM codend with a very low escape ratio (10%).

An experimental study was carried out to know the square mesh codend in trawl net by using different bridle lengths viz. 15 m and 20 m bridle length at a depth of 20 m. The study was carried out once in the month for a period of five months. The catch found was 8.7 kg and 13.5 kg for cover codend of 0day to the 15 m and 20 m bridle length respectively. As far as the 30th days are concerned, the catch obtained were 10.02 kg and 20.60 kg for 15 m and 20 m bridle length respectively. During the 60th day, the catch obtained was 12.02 kg and 30.50 kg for 15 m and 20 m bridle length respectively. At a depth of 20 m, the catch obtained for 90th day was 15.7 kg and 27.6 kg for the square mesh codend used with 15 m and 20 m bridle length respectively. Similarly for 120th day, the catch obtained was 14 kg and 25.5 kg for 15 m and 20 m bridle length respectively. During the study period, it was also observed that the diamond mesh was used as cover codend for the square mesh codend trawl net to know the escapement of fishes with 8.70 kg, 13.52 kg, 8.50 kg, 13.10 kg, 10.19 kg, 12.00 kg, 10.70 kg and 12.50 was observed for 0, 30th, 60th, 90th and 120th days respectively for the square mesh codend trawl net with a bridle length of 15 m and 20 m respectively. It was noticed that at a depth of 20 m, for a 20 m bridle length was found suitable for carrying the trawl net fishing operation commercially. [ABSTRACT FROM AUTHOR]

The study was carried out by using trawl fishing gear along Mangaluru coast off Karnataka. This mid water was carried out from stern trawling. The study was carried out once in fortnight for a period of four months. The wing trawl type gear was the trawl net that was used more than that of any other type of trawl net. In survey studies, wing trawl is attached with 35 mm square mesh codend. The square mesh codend is attached to trawl net. The diamond mesh was used as a cover codend for setting up on the square mesh codend to calculate the escapement of fish catches in percentage. With this escapement percentage, the retention percentage is also calculated. The escapement percentages have been helped to find out the amount of catch escaped and retention catch percentage, which would enable to calculate profit of that particular trip. [ABSTRACT FROM AUTHOR]

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In the English Channel and Southern Bight, French demersal trawlers target a mix of demersal species including whiting ( Merlangius merlangus ). The discard ban to be implemented in January 2016 motivated fishermen to look for technical measures to reduce unwanted catches of undersized individuals (<27 cm). From 2008–2014, 18 different gear configurations were tested for bycatch reduction on board fleets of vessels of 16–20 m and 20–24 m. Selective devices tested included grids, square mesh panels (SMP), square mesh cylinders (SMC), various combinations of these devices and large mesh trawls. Using the catch comparison method, our results focus on six devices that proved efficient to reduce catches of undersized whiting, equally divided between the two vessel size groups. Large mesh trawls are not adequate to improve whiting size selectivity with losses of commercial size fish. The mandatory 80-mm SMP was efficient at letting undersized whiting escape from the trawl for both vessel length classes. Its efficiency was enhanced when it was positioned 6–9 m ahead of the codline compared with that placed at 12–15 m. The most appropriate bar spacing for whiting size-selectivity was found in a flexigrid with 23 mm bar spacing, but this required a large portion of square mesh netting to be installed ahead of it (SMP and SMC) to limit catches of undersized individuals. The most promising device tested was an 80 mm SMC, either 2 m long and used alone or 1 m long and used in association with the mandatory SMP; these setups allowed significant escapes of fish up to 25 cm in length. For both SMP and SMC, a mesh size equal to or larger than 100 mm led to losses of commercial size whiting. [ABSTRACT FROM AUTHOR]

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 L50 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 L50 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 L50 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).

A traditional codend (40 mm diamond mesh) and an experimental codend (40 mm square mesh) made of 2.6 mm diameter knotless PA netting were tested on a commercial trawl net on a sandy-muddy bottom (~70 m depth) of the Adriatic sea in order to assess the size selectivity of European hake (Merluccius merluccius) and the reduction of the discards in a demersal multi-species trawl fishery. The catch was sorted as target species and bycatch and the selectivity with respect to European hake was investigated using the covered codend method. The square-mesh codend allowed a reduction of about 37% of the fraction discarded at sea. The mean catch obtained with the experimental codend was lower than that obtained with the traditional codend (about 14 kg per haul) but the short-term economic losses were low (~12%). The square-mesh codend was also more selective than the traditional codend, giving the juveniles of European hake a good chance of escape: the mean selection length (L50) was 7.60 cm in DM and 12.98 cm in SM. Moreover, the mesh configuration did not affect the gear’s performance. Thus, the square-mesh codend could be an easy, inexpensive and useful solution for a more sustainable management of the resources in Adriatic multi-species fishery.

La evaluación de paneles de escape de malla cuadrada en redes de arrastre de fondo usadas en la pesquería de merluza común se realizó empleando dos metodologías complementarias: lances con sobrecopo y lances alternados. Los lances con sobrecopo permitieron cuantificar la fracción de la captura que escapa a través de los paneles de escape, y determinar la estructura de tallas y pesos medios, estimando longitudes de retención y rangos de selección. Se determinó la fracción bajo 30 y 36 cm de longitud total presentes en el copo y en el sobrecopo, ambos como indicadores del efecto selectivo que éstas producen. Los lances alternados permitieron verificar la disminución de los rendimientos de captura, tanto en número como en peso, aumentando los pesos medios de los ejemplares retenidos y disminuyendo la proporción de ejemplares bajo tallas de referencia, lo que indica la existencia de un efecto de escape en la fracción juvenil del stock.The evaluation of square mesh escape panels in bottom trawl nets used in the common hake fishery was carried out employing two complementary methodologies: top cover and alternated hauls. The top cover hauls were used to quantify the fraction of the catch that escapes through the panels and to determine the size structure and mean weight of the catch, estimating the retention sizes and selection ranges. The fractions under 30 and 36 cm of total length present in the codend and in the top cover were determined as proxies for the selective effect produced by the escape panels. The alternated hauls were used to verify the decrease in the catch rate, both in number and in weight, increasing the mean weight of the retained catch and decreasing the proportion under the reference length, for which we concluded that an escape effect does occur on the young fraction of the stock.

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 (L50) 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 L50 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 L50 of 14.3 cm indicates that larger grid spacing is required to attain an L50 that would be close to the current MLS (18 cm). For Atlantic horse mackerel and red mullet, the L50 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.

The Mediterranean fishery has experienced a decline in catches over the past 20 years due to an excessive increase in effort caused by both increased trawler engine power and rapid technological advances in fishing technology and fish location. This has led to overexploitation, in which immature individuals support an increasing portion of the catches. The present study was undertaken to test a sorting grid and square-mesh-panel as juvenile exclusion systems. Our experience was a pilot study of such a system in the western Mediterranean. The purpose of these exclusion systems was to help juvenile hake escape from the net. The results demonstrate that the use of sorting grids for small fish in trawl gears in the Mediterranean is an efficient and practical means of avoiding the capture and discarding of unwanted individuals, with escape rates of over 50% (ranging between 50 and 90%). The grids were efficient and useful for excluding hake (Merluccius merluccius) on bottoms located at depths between 50 and 300 m, where hake are found all year round. A bar spacing of 20 mm yielded escape rates of L50 at 18.8 cm TL (L25 = 16.8 cm and L75 = 20.9 cm). Panels made of square meshes achieved poorer results than the grids. The grid system was effective for most of the species caught in the study area.

Poor selectivity of demersal trawls targeting fish, crustaceans and cephalopods in Mersin Bay, Turkey, (and more broadly for most Mediterranean demersal trawlers) is a significant concern. The majority of the boats working in the Mersin Bay trawl fishery use traditional gears with 44 mm mesh size hand-woven slack knotted codends in which approximately 50% of the catch by weight and 70% by numbers are discarded. The present study compares size selectivity of a commonly used hand-woven codend and three alternative machine woven codends (40 mm square mesh; 44 mm and 50 mm diamond mesh) for seven commercial species: red mullet ( Mullus barbatus ); brushtooth lizardfish ( Saurida undosquamis ); common pandora ( Pagellus erythrinus ); goldband goatfish ( Upeneus moluccensis ); Randall's threadfin bream ( Nemipterus randalli ); green tiger prawn ( Penaeus semisulcatus ); and speckled shrimp ( Metapenaeus monoceros ). A total of 87 hauls were conducted using a covered codend method in 2011. Short term commercial loss for 31 marketed species resulting from switching from the commercial codend to each alternative codend, was estimated. Results show that size selectivity of the commercial codend is rather poor for almost all the marketed species. The 40 mm square mesh codend is the best alternative for the majority of the marketed species in terms of releasing juveniles. We estimate a commercial loss of 17% in landing values if this codend is used. [ABSTRACT FROM AUTHOR]

Abstract: Five modified trawl codends were assessed for their utility in simultaneously improving the size selectivity of cod (Gadus morhua) and plaice (Pleuronectes platessa) in the Baltic Sea. The modifications included refining the selective performance of the current Bacoma codend by increasing the mesh size of the lower panel from 109mm double twine to 129mm single twine and increasing the mesh size in the upper square mesh panel from 132 to 147mm, and also making the lower panel the same design as the upper panel; i.e. a full square mesh codend. These three experimental designs were tested in conjunction with the currently legislated codends; Bacoma and T90. The most favourable selective properties with regard to simultaneously improving the selectivity for round and flatfish, considering the current minimum landing sizes (MLS) for cod (38cm) and plaice (25cm) in the Baltic Sea and the fish population size structures during the sea trials, were found to be the T90 codend and the Bacoma codend with a modified lower panel. For the T90 codend, the selection parameters (L50 and SR) were 43.4 and 6.7cm for cod, and 24.7 and 2.1cm for plaice. The selection parameters for the most effective modified Bacoma codend were 41.1 and 8.3cm for cod and 25.2 and 3.9cm for plaice [Copyright &y& Elsevier]

Abstract: We investigated the survival of red mullet (Mullus barbatus), annular seabream (Diplodus annularis), and blotched picarel (Spicara maena) escaping from 40mm square and 40mm diamond mesh codends in the Aegean Sea. A low mortality for red mullet and blotched picarel was observed, and annular seabream had no mortality for two different codends. Red mullet mortality for diamond mesh codends was greater than square mesh codends. The estimate of the mean survival rate of square mesh codends for red mullet was 95.1%, while diamond mesh codends were 81.2%. For blotched picarel, the mean proportion surviving in the 3 square mesh codends was 96.5%, whereas it was 91.2% for diamond mesh codends. Mean survival percentages of brown comber (Serranus hepatus) were 96.7 and 94.6 for square and diamond mesh codends, respectively. Mortalities of scaldfish (Arnoglossus laterna) and survival rates of common pandora (Pagellus erythrinus) were 100.0% for all the cages. [Copyright &y& Elsevier]

Abstract: We describe how discarding can be significantly reduced by incorporating some simple gear modifications to a beam trawl. These modifications were developed by the fishing industry in response to public concerns on the relatively high levels of discards in their fishery (ca. 70% discard rate). A national competition specifically created to facilitate the engagement of industry successfully resulted in the development of these gear-based discard solutions. The modifications produced discard reductions of around 60% (by number) and have been used on a continuous commercial basis for more than a year by the competition winner. All beam trawls used in the UK beam trawl fleet are similar in design, but we demonstrate that the modifications outlined here may not be universally acceptable across the whole beam trawl fleet, primarily because of the diversity in species targeted. This supports the idea that vessel-based discard mitigation targets might be a more effective tool than prescriptive gear technology legislation in the management of discard reduction. [Copyright &y& Elsevier]

Abstract: A comprehensive set of experiments using the twin trawl technique were conducted in the North Sea to assess the selectivity of haddock (Melanogrammus aeglefinus), cod (Gadus morhua) and saithe (Pollachius virens) in 120mm mesh cod-ends with (i) 100, 80 and 60 meshes in circumference; (ii) a 35mm ‘flexi-grid’ mounted in the extension; (iii) a 110mm ‘Bacoma’ style square mesh panel. For haddock, cod-end type and catch size had a significant impact on 50% retention length (L50) and only cod-end type influenced selection range. Reducing the number of meshes in circumference from 100 to both 80 and 60 increased the L50 of haddock. The Bacoma panel gave a similar selection for haddock to the 60 mesh round cod-end, while no difference was found between the ‘standard’ 100 meshes round cod-end and the trawl with the flexi-grid fitted. For saithe, the cod-end with 60 meshes in circumference was significantly more selective than the cod-end with 100 meshes around. The cod-end with 80 meshes in circumference had an estimated selectivity between that of the cod-ends with 60 and 100 meshes in circumference, although it did not differ significantly from either. Catch size was not found to influence the selectivity of any of these three cod-ends. Insufficient data were obtained to estimate either the selectivity of saithe in the cod-end with a Bacoma panel or grid. A stock predictive model was used to illustrate the possible long-term effects of improving gear selectivity on the biomass, yield and discarding of haddock in the North Sea. [Copyright &y& Elsevier]

The evaluation of square mesh escape panels in bottom trawl nets used in the common hake fishery was carried out employing two complementary methodologies: top cover and alternated hauls. The top cover hauls were used to quantify the fraction of the catch that escapes through the panels and to determine the size structure and mean weight of the catch, estimating the retention sizes and selection ranges. The fractions under 30 and 36 cm of total length present in the codend and in the top cover were determined as proxies for the selective effect produced by the escape panels. The alternated hauls were used to verify the decrease in the catch rate, both in number and in weight, increasing the mean weight of the retained catch and decreasing the proportion under the reference length, for which we concluded that an escape effect does occur on the young fraction of the stock. [ABSTRACT FROM AUTHOR]

The demersal multispecies trawl fishery in the western Mediterranean Sea has a poor selectivity; large numbers of juvenile fish are caught when using the legislated 40-mm diamond mesh cod end. The selectivity of a flexible sorting grid with 20-mm bar spacing (BS20) installed in front the conventional trawl cod end was investigated. The standard covered cod end method was used. Data was adequate for analyzing the selectivity of European hake Merluccius merluccius, poor cod Trisopterus minutus, greater forkbeard Phycis blennoides and Norway lobster Nephrops norvegicus. The selectivity of the 20-mm sorting grid was compared with the performance of 40-mm diamond (DM40) and square mesh (SM40) cod ends. The effect of a guiding funnel on the performance of the grid (BS20-f) was also explored. Finally, the potential changes in yield per recruit (Y/R) and biomass per recruit (B/R) after implementing a sorting grid were explored. An overall improvement in the 50% selection length ( L 50) with all four species was substantial when comparing the BS20 to the DM40. Higher improvement in L 50s was achieved when the grid was equipped with the guiding funnel. When comparing the performance of the BS20-f to the SM40, there was no marked difference in L 50s. The Y/R and B/R, however, are substantially higher with BS20-f for poor cod and about the same for European hake. BS20 compared to SM40 achieved lower Y/R and B/R for all four species; the smallest difference was observed for Norway lobster. Further development is required if the sorting grid is to be introduced into commercial fisheries. [ABSTRACT FROM AUTHOR]

Abstract: A covered-codend experiment was done to assess the size selectivity of a codend made from 27-mm mesh hung on the bar (i.e. square mesh) for school prawns (Metapenaeus macleayi) across 10 vessels within the New South Wales (NSW) estuarine penaeid-trawl fishery. Prior to starting the experiment, a codend cover (18-mm diamond-shaped mesh) was tested and demonstrated to have no effect on the catching efficiency of a typical estuarine trawl, thereby validating its use for assessing size selectivity. There was substantial variability in the estimated carapace lengths at 50% probability of retention (L 50 ±S.E.: between 7.90±0.97 and 13.76±0.23mm) and selection ranges (SR: between 2.70±0.18 and 6.71±1.72mm) of the 27-mm square-mesh codend among trawlers and estuaries. Multi-level, generalised linear mixed-effects modelling demonstrated that this variation was explained by: (i) the catch weight of school prawns; (ii) the particular estuary being fished; and (iii) random between-tow and -trawler variability. The results are discussed in terms of the various operational, biological and environmental factors unique to each fishing operation. Despite the variability in the performance of the 27-mm square-mesh codend, an overall improvement in size selectivity compared to conventional diamond-mesh designs, combined with a high survival rate of escapees, justifies its adoption and legislation throughout the NSW estuarine penaeid-trawl fishery as a means for mitigating unwanted fishing mortalities. We also conclude that similar codends may have application in other penaeid-trawl fisheries around the world. [Copyright &y& Elsevier]

Abstract: Trials were carried out to evaluate the effects of a square mesh panel on the catches of a demersal trawl during normal commercial fishing operations over a period of 1 year. A 100mm cod-end fitted with a 90mm mesh square mesh panel between 6.3 and 9.3m from the cod-line was compared with an identical cod-end with no panel, attached to the same net, using the alternate haul method. The square mesh panel significantly reduced the catch of undersized whiting (by an estimated 34%; p <0.001) and of whiting greater than the minimum landing size up to lengths of about 32cm (p <0.05). However, the square mesh panel had no significant effect on the catches of haddock, cod or monkfish. Hauls with a small-mesh cod-end showed that large numbers of small haddock were present in the areas where the trials were carried out. Few of these fish were retained by the normal cod-end, either with or without the square-mesh panel, suggesting that fitting the square mesh panel did not appreciably improve the selectivity of the cod-end design used in these trials. [Copyright &y& Elsevier]

Abstract: Selectivity properties of five codend types were evaluated using the covered codend method. The codends tested were 152, 165 and 178mm diamond mesh codends, and 165 and 178mm square mesh codends. A new hydrodynamic codend cover, which was expanded by 12 water-borne kites, was developed, tested and used during the codend mesh selectivity studies. Eighty-six successful tows were completed for the five codends. This paper describes results for two species of roundfish – Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) and four species of flounders – American plaice (Hippoglossoides platessoides), yellowtail flounder (Limanda ferruginea), witch flounder (Glyptocephalus cynoglossus) and winter flounder (Pseudopleuronectes americanus). The results indicate that larger codend mesh sizes retained larger fish for all species for both diamond and square mesh codends. The mesh shape (diamond or square) has no significant effect on the 50% retention length (L 50) for roundfish (P >0.1) while the square mesh codends have significantly smaller L 50s for flounders (P <0.001). The square mesh codend has a narrower selection range (SR) than the corresponding diamond mesh codend for both cod and haddock. [Copyright &y& Elsevier]

Abstract: Commercial fishing trials with 40mm diamond (DM40) and square (SM40) mesh codends made of 5mm diameter knotted PE-netting were conducted in July 2005 on the continental shelf (∼100m) and upper slope (∼400m) of the Catalan Sea (NW Mediterranean) to assess the size selectivity of European hake (Merluccius merluccius), Norway lobster (Nephrops norvegicus), poor cod (Trisopterus minutus) and greater forkbeard (Phycis blennoides) in the demersal multi-species trawl fishery. In total, 28 tows were done using the standard covered codend method. For all four species, the SM40 showed a significantly higher mean selection length (L 50) than the DM40. For hake the L 50 was 16.0cm in SM40 and 10.1cm in DM40; the corresponding figures were 13.0cm versus 9.2cm for poor cod and 14.9cm versus 9.8cm for greater forkbeard. For Norway lobster, DM40 did not show any size-selectivity whereas SM40 produced a L 50 of 22mm. The selection range (SR) between DM40 and SM40 was not significantly (p >0.05) different for any of the three fish species. Our trials indicate that substantial improvement in size-selectivity for these commercially important species is achieved by switching from the conventional 40mm diamond mesh codend to a 40mm square mesh codend. Our analysis also suggests that by using a 40mm square mesh codend the short-term economic losses of commercial species, compared to the losses of 40mm diamond mesh codend, will be low in the slope fishery (less than ∼5% of the total catch value), whereas in the continental shelf losses could be up to ∼30% of the total catch value. [Copyright &y& Elsevier]

Selectivity experiments of diamond and square mesh codends with different mesh size (30, 35, 40 and 45 mm) for hairfin anchovy Setipinna taty were carried out using the covered codend method in Chinese stow net fisheries. In the present study, 5151 specimens were subsampled and asymmetric and symmetric selectivity curves (Richards and Logistic curves) were fitted to the catch data, using the maximum likelihood method according to the SELECT model. The results show that the Richards curve gives a better fit to the selectivity curve for diamond mesh codends with 30, 35 and 40-mm mesh sizes, whereas the logistic curve gives a better fit for the diamond mesh codend with 45 mm mesh size and square mesh codends with 30, 35, 40 and 45-mm mesh size. With the exception of 45-mm mesh size codends, the L50 of diamond mesh codends were insignificantly larger than those of square mesh codends. However, the selectivity curves of square mesh codends were steeper than those of diamond mesh codends, except the 30-mm mesh size codends. As for diamond mesh codends, according to the linear relationship between the L50 and mesh size, 36.5-mm mesh size codends could release 50% juvenile hairfin anchovy (below 1-year old). However, diamond mesh codends with such a mesh size are not selective for other species. [ABSTRACT FROM AUTHOR]

Poor selectivity of conventional trawl codends has recently been a serious concern in Turkish fisheries. Modification of the codends to reduce the capture of juvenile fish has been one of the management tools for sustainable fisheries. This study investigates effect of square mesh escape window installation on selectivity of bottom trawl codends for red mullet (Mullus barbatus), annular sea bream (Diplodus annularis) and common pandora (Pagellus erythrinus) in the Aegean Sea. Codend mesh selectivity experiments were carried out using 40 mm nominal diamond mesh PE codend with a square mesh escape window inserted in the forward part of the top panel. The experiments were carried out in Ýzmir Bay in the eastern Aegean Sea between 24th June and 31st July 2002 on board R/V "Egesüf". A total of 9 valid hauls were made by using hooped covered codend method. Selectivity parameters were obtained by using logistic equation with the maximum likelihood method. Mean L50s and selection ranges of the window installed codend were found as 12.55 (se 0.18) and 2.27 (se 0.06) cm for red mullet, 9.49 (se. 0.27) and 1.26 (se. 0.05) cm for annular sea bream and 12.18 (se 0.31) and 2.00 (se 0.07) cm for common pandora, respectively. Comparison of the results with those obtained in other studies carried out in the same area by using conventional codends show that the use of square mesh escape window in the forward part of the top panel increases the escape of juvenile red mullet, annular sea bream and common pandora. [ABSTRACT FROM AUTHOR]

Twin-trawl experiments were conducted to assess how the position of a 90 mm square mesh panel affects haddock and whiting selectivity. The panel was 3 m long and was placed 9–12, 6–9 and 3–6 m from the cod-line, the rearmost part of the cod-end. A net with no panel was also used for comparison. Inserting the panel 3–6 m from the cod-line had the greatest effect, increasing the L50 of both haddock and whiting by ∼4.5 cm. Inserting the panel 6–9 or 9–12 m from the cod-line increased the L50 of both species by 1–2 cm, although the increases were only statistically significant for haddock. [Copyright &y& Elsevier]