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WOS: 000496712500011, A large part of the total whiting (Merlangius merlangus euxinus) fishing in the Black Sea is carried out with the traditional bottom trawl nets along the coast of Turkey. Diamond mesh shape with 40 mm mesh size (40D) has been used in the codends of these trawls. in this study, the traditional trawl codend (40D) and square-mesh codend with different size (36S and 40S) were compared for whiting size selectivity in August 2014. Selectivity data were collected by using a covered codend method and analysed taking between haul variations in to account. the selectivity parameters were estimated by using CC2000 software. Results showed that commercially used 40D trawl codend is not selective enough to release immature of whiting. However, the net change in square mesh (36S and 40S) instead of a diamond-shaped (40D) mesh significantly improved the mesh selectivity for whiting. the 40S trawl codend is even higher than the first maturity size (L-M50) with a length at fifty percent retention (L-50) of 15.74 cm. in conclusion all square mesh codends with different mesh size tested here supplied appropriate selection considering minimum landing size (MLS) of whiting., European Project "BENTHIS [EU-FP7-312008], This work was financed by the European Project "BENTHIS (EU-FP7-312008)". the authors would like to thanks and gratitude to the project leader Prof. Dr. Adrian RJINSDORP providing all kinds of support. Thanks are also due to all the project researchers for participating the sea trials.

Mediterranean trawl fisheries are characterized by a critical combination of high fishing effort and low size at first capture for most commercial species. In this study we tested the use of sorting grids installed on bottom trawl nets to minimize the catch of undersized deep-water rose shrimp (Parapenaeus longirostris, DPS) and European hake (Merluccius merluccius, HKE). The catch of a traditional trawl net was compared with that obtained with the same net equipped with ad hoc designed juveniles and trash excluder devices (JTEDs) during an experimental survey. Three different JTEDs were tested: the first (G1-SM40) was built with a net of 40-mm square mesh; the second (G2-ST20) and third (G3-ST25) with vertical steel bars spaced 20 and 25 mm, respectively. The probability of retaining DPS and HKE by length class in trawl nets with and without JTED was analysed using generalized additive mixed models. With G1-SM40, the reduction of undersized individuals in the cod-end was about 60% and 44% for DPS and HKE, respectively. With G2-ST20, a 34% catch decrease of HKE individuals smaller than 20 cm total length was observed. A loss of marketable fractions of DPS was recorded with G1-SM40 (–25%) and G2-ST20 (30%). Finally, JTD G3-ST25 was efficient at reducing the catch of undersized specimens of DPS and HKE, but showed a higher loss of marketable fractions than the other JTEDs. Although further fishing trials would be required to maximize the sorting efficiency of the grids, the results obtained clearly indicated that grids can substantially reduce unwanted catches of undersized DPS and HKE in Mediterranean bottom trawl fisheries., Las pesquerías de arrastre mediterráneas se caracterizan por una combinación crítica de un alto esfuerzo de pesca y un tamaño de captura por debajo de la talla legal para la mayoría de las especies comerciales. En este estudio, probamos el uso de rejillas separadoras instaladas en redes de arrastre de fondo para minimizar la captura de la gamba rosada (Parapenaeus longirostris; DPS) y la merluza (Merluccius merluccius; HKE). La captura obtenida con una red de arrastre tradicional se comparó con la obtenida con la misma red equipada con “Juveniles Trash Excluder Devices” (JTED) diseñados específicamente para cada caso durante un estudio experimental. Tres JTEDs diferentes se probaron: el primero (G1-SM40) se construyó con una res de 40 mm de malla cuadrada; el segundo (G2-ST20) y el tercero (G3-ST25) se fabricaron con barras verticales de acero separadas 20 y 25 mm, respectivamente. La probabilidad de retener DPS y HKE según clase de talla en redes de arrastre con y sin JTED se analizó utilizando Modelos Mixtos Aditivos Generalizados (GAMM). Usando G1-SM40, se consiguió una reducción de individuos de talla por debajo de la talla legal en el copo, de 60% y 40% para DPS y HKE respectivamente. Con respecto a HKE, utilizando G2-ST20 se observó una disminución en la captura del 34% de individuos de menos de 20 cm TL. Sin embargo, se registró una pérdida de fraccion comercializable de DPS usando G1-SM40 del –25% y usando G2-ST20 del 30%. Finalmente, el JTED G3-ST25 resultó eficaz para reducir la captura de especímenes de DPS y HKE de talla ilegal, pero se observó una mayor pérdida de fraccion comercializable que con los otros JTEDs. Aunque se necesitarían más ensayos de pesca para maximizar la eficiencia de las rejillas separadoras, los resultados obtenidos indicaron claramente que las rejillas pueden contribuir a reducir sustancialmente las capturas no deseadas de DPS y HKE de talla ilegal en las pesquerías de arrastre de fondo del Mediterráneo.

The reduction of juvenile catch and discards are important targets in fisheries policy. This work examines how selection models can predict the size structure (LFD) of discards and landings considering the effects of area, time period, gear and fisher behaviour. Additional exploitation indicators related to the gear used, fisher's selection pattern, and discards were also estimated. The approach is demonstrated in a study concerning hake in the Mediterranean trawl fishery, focusing on high (HRA) and low (LRA) recruitment areas in the Saronikos Gulf (Eastern Mediterranean) during two periods (June, September) using two codends (40 mm square-40S, 50 mm diamond-50D mesh). The predicted discards LFDs revealed generally higher percentages in the HRA in June when using the 50D. The predicted landings LFDs showed higher percentages in the LRA in September for both codends, but undersized hake were always included. LFDs and exploitation indicators indicated that both codends were inappropriate for sustainable fishing of hake in the HRA, where 50D performed worse than the 40S. Fishing with both codends in the LRA in September revealed the lowest discards rates and minimum sizes of landings close to MCRS (minimum conservation reference size). These results can provide information to fisheries management aiming to protect juveniles and reduce discards through spatio-temporal fishing closures.

Reduction of discards from the Basque mixed bottom trawl fishery is a challenge. To improve the selective properties of the gear used by the fleet and supplement codend size selection, a square mesh panel (SMP) installed in the upper panel of the trawl was introduced in 2006. However, recent studies have shown that the release efficiency of this SMP is low due to lack of contact between the fish and the SMP. In this study, we tested the release efficiency of the SMP for four different gear configurations. We tested the effect of adding LED lights at two different positions and altering panel size and panel position in the trawl. The analyses were focused on two species: hake (Merluccius merluccius) and blue whiting (Micromesistius poutassou). The results showed that the position of LED lights did not significantly affect the SMP’s release efficiency for any species. However, increasing panel size had a significant positive effect on the release efficiency of blue whiting, and placing the SMP in the lower panel improved the release efficiency of hake. These results highlight the challenge of simultaneously improving the selective properties of gear for species with different behaviour, especially in mixed demersal fisheries. La reducción de descartes en la pesquería de arrastre del País Vasco supone un problema importante. En 2006, se introdujo en la reglamentación la posibilidad de usar un Panel de Malla Cuadrada (SMP) en la zona anterior al copo para mejorar la selectividad de la red. Sin embargo, estudios recientes manifiestan que la eficiencia de escape de los peces es baja debido a la falta de contacto selectivo entre el pez y el panel. En este estudio, analizamos la eficiencia de diferentes configuraciones del SMP. Se analizó el efecto de luces LED colocadas en distintas posiciones, el efecto del tamaño del SMP y su localización. Estudiamos la merluza (Merluccius merluccius) y la bacaladilla (Micromesistius poutassou). La posición de las LED demostró no tener ningún efecto significativo sobre la eficiencia de escape del SMP para ninguna de las dos especies. Sin embargo, aumentar el área del panel tuvo un efecto significativo en la eficiencia de escape de la bacaladilla, mientras que el cambio de posición del SMP incrementó la eficiencia de escape de la merluza a través del SMP. Estos resultados muestran el reto que supone mejorar la selectividad de un arte de pesca simultáneamente para especies demersales con comportamientos diferentes.

Creative Commons Attribution Non-Commercial Share Alike License 3.0 CC BY-NC-ND 3.0. The current legal codends used in Mediterranean bottom trawl fisheries are at high risk of retaining undersized individuals of several commercial fish species. This entails that codends alone are unable to provide the desired exploitation pattern. A simple technological measure that potentially can provide higher release efficiency of undersized fish are Square-Mesh Panels (SMPs). SMPs are often applied in the upper section of the trawl belly, just ahead the codend. However, recent studies in the Mediterranean have demonstrated that SMPs mounted in this position provided limited release efficiency, because very few fish came into contact with their meshes. In attempt to improve SMPs efficiency in the Mediterranean bottom trawl fisheries, we applied them on the lateral sides of the last tapered section of the trawl belly, just ahead of the codend, and fitted two guiding panels in the trawl belly to enhance fish-SMP contact. We compared the catch performance of a standard commercial trawl with a 52 mm diamond-mesh codend and of a similar trawl fitted with lateral SMPs (70 mm mesh size) in the belly using a twin trawl. The study focused on red mullet (Mullus barbatus), a commercially important species, but data for gurnard (Chelidonichthys lucerna and Chelidonichthys cuculus) were also obtained and analysed. In contrast to previous research on SMPs mounted in the top panel of the trawl, in this study SMPs induced a significant effect on catch performance for red mullet, demonstrating that their lateral position involved greater fish-SMP contact. However, since the test trawl lost a significant amount of legal-sized red mullet compared with the standard trawl, the effect was not wholly positive, possibly due to an excessively large mesh size. Therefore, future studies should be encouraged to test lateral SMPs with smaller mesh sizes.

This is a pre-copyedited, author-produced version of an article accepted for publication in ICES Journal of Marine Science following peer review. The version of record Cuende, E., Arregi, L., Herrmann, B., Sistiaga, M. & Aboitiz, X. (2020). Prediction of square mesh panel and codend size selectivity of blue whiting based on fish morphology. ICES Journal of Marine Science is available online at: https://doi.org/10.1093/icesjms/fsaa156 Square mesh panels (SMPs) are selective devices used extensively to supplement codend size selectivity in trawl fisheries. Therefore, predictions of the effect of mesh size in both SMPs and codends on size selectivity are valuable. Here, we established a framework to predict the size selection of blue whiting through different SMPs and diamond mesh codends based on the morphological characteristics of this species. We hypothesized that size selection for an SMP is determined by different fish contact angles, whereas different mesh opening angles determine size selection for the codend. Based on these hypotheses, we first developed a model that enabled us to predict which sizes of blue whiting are able to pass through meshes of different sizes and shapes. We then tested whether the selectivity for blue whiting of the SMP, the codend, and the combination of both could be explained by the models. Finally, we predicted the size selectivity of multiple combinations of SMPs and diamond mesh codends. The method presented here can potentially be applied to make predictions for species other than blue whiting.

Bottom-trawl fishing for crustaceans off the Portuguese south and southwest coasts is a very important segment of the Portuguese fishing fleet, where annual rates of discarding have ranged from approximately 38% to as much as 70% of the total catch. Past experiments to address this problem encompassed the testing of different codend mesh sizes and configurations, square mesh windows and rigid grids to enhance species and size-selectivity. While the use of a Nordmore grid has proved quite efficient in separating out blue whiting (Micromesistius poutassou), it also led to some losses of the two main crustacean target species, Norway lobster (Nephrops norvegicus) and rose shrimp (Parapenaeus longirostris). The present study addresses that limitation by using a modified grid with 20 mm bar spacing and two open sections, designed with the purpose of separating fish and crustacean species into upper and lower codends. Good separation was achieved, with about 80% of the blue whiting (in number) directed towards the upper trawl section and caught in the upper codend, while a similar percentage of Norway lobster was caught in the lower codend. The grid bars had 50% retention for Norway lobster at 34.1 mm carapace length. The results herein will enable this gear configuration to be finetuned with regard to codend mesh sizes and bar spacing, so as to optimize both retention of Norway lobster and exclusion of blue whiting. For example, compared to using the minimum 70 mm diamond mesh size, using an 80 nun diamond mesh upper codend would reduce Norway lobster catch weight by just 1.6% but reduce the number of blue whiting caught by 42%. [22-05-01-FDR-00014]

WOS: 000438656900006 Background. the beam trawl fisheries of veined rapa whelk, Rapana venosa (Valenciennes, 1846), cause small benthic organisms to be captured and also damage the other species living on the seafloor. To solve this problem, a proper modification that minimise the by-catch should be designed and put into practice. This study aims to compare 72 mm commercial diamond-mesh codend with 72 mm square-mesh codend to reduce the benthic bycatch in this fishery. Materials and methods. Totally 15 hauls were carried out in south-eastern Black Sea Region within 10-14 August 2017. A commercial diamond-mesh and square-mesh beam trawls were towed simultaneously behind a commercial fishing vessel to compare the by-catch compositions. Paired t-test was used to compare the catch amount of two codends based on species. GLMM (Generalised Linear Mixed Models) was used to compare the length of captured veined rapa whelk, mussel, and crab species. Results. There was a 77-percentage-point reduction in the mean number of the captured individuals as by-catch in square-mesh codend when compared with commercial diamond-mesh codend and this difference was found statistically significant (P < 0.05). A total of 17 species was captured as by-catch in both codends. Comparing to diamond-mesh codend, the catch amount of the 13 by-catch species had decreased in square-mesh codend. Conclusions. in conclusion, the square-mesh codend was found successful in decreasing the by-catch amount of many benthic species except for flatfish species and large crabs. in addition to this, the veined rapa whelk amount fell by half and this means a 25-percentage-point profit decrease for fishermen. Recep Tayyip Erdogan University Research Project FundRecep Tayyip Erdogan University [FBA-2017-781] I would like to thank the captains and crews of the FV Piryoz 53. Thanks are also extended to Dr Goktug Dalgic and Yusuf Ceylan for their help in the sea trials. This study was financed by the Recep Tayyip Erdogan University Research Project Fund (Project No: FBA-2017-781).

We tested the ability of stimulators to improve the release efficiency of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) through the meshes of a square mesh section installed in a trawl. The section was tested in three different configurations: without any stimulation device, with a mechanical stimulation device, and with LED light stimulation devices. We analysed and compared the behaviour of cod and haddock in all three configurations based on release results and underwater recordings. Parallel to the fishing trials, we carried out fall-through tests to determine the upper physical size limits for cod and haddock to be able to escape through the square meshes in the section. This enabled us to infer whether lack of release efficiency was due to fish behaviour or release potential of the square meshes in the section. The results showed that the escape behaviour of haddock can be triggered by mechanical stimulation. In contrast, cod did not react significantly to the presence of mechanical stimulators. LED light stimulation had some effect on the behaviour of haddock, but not on cod.

Demersal seining is an important fishing method to harvest cod (Gadus morhua) in Norwegian fisheries. Knowledge about size selectivity of cod in this type of fishing gear is therefore of importance for managing the exploitation of cod resources. However, limited data exist on the size selection of cod in the square mesh codends mostly applied in this fishery. By using knowledge of fish morphology and the computer-based simulation method FISHSELECT, we investigated the potential for size selection of cod in square mesh codends for demersal seining. We were able to explain and understand existing experimental selectivity results and predict the effect of design changes in the codend. The results showed that the currently applied codend designs are adequate to ensure low catches of cod below the minimum size for this fishery, but they also indicated that a considerable part of the size selection may occur through slack meshes. Thus, it is likely that part of the codend mesh selection may occur when the gear is at the surface.

We used fish body depth to predict trap center-to-center mesh sizes that would optimize size selection of black sea bass Centropristis striata for both current and proposed minimum size limits for this species. We fished trap types of five different square mesh sizes/configurations: (1) 38.1 mm mesh, (2) 38.1 mm mesh on five sides and 50.8 mm mesh on one side (back panel trap), (3) 50.8 mm mesh, (4) 57.2 mm mesh, and (5) 63.5 mm mesh. The 38.1 mm mesh trap was the control trap type. Back panel traps are the minimally legal mesh configuration in this region while 50.8 mm mesh traps are commonly used in this fishery to further reduce culling of sub-legal black sea bass by fishers. Two previously untested mesh sizes, 57.2 and 63.5 mm, were evaluated because a previously published morphometric relationship between black sea bass body depth and total length (TL) predicted that the diagonal openings of these two respective mesh sizes would retain black sea bass close to the current (279 mm) and proposed minimum TL limits (305 mm). We estimated size selection of each experimental trap type by comparing catches of control and experimental traps. All but the back panel trap displayed relatively steep selection around the fish length at which 50% of individuals were selected ( l 50 ). Initial size at retention ( l 10 ) by the 57.2 and 63.5 mm trap types were nearly identical to current and proposed minimum fish sizes, respectively. Predictions from the body depth: TL relationship were very similar to estimates of l 10 and l 50 , based on uncompressed body depth and compression to 93%. The 57.2 mm mesh and 63.5 mm mesh trap types maintained catches of legal fish but reduced catches of sub-legal fish compared to the back panel and 50.8 mm mesh trap types. Relative to back panel and 50.8 mm mesh traps, use of 57.2 mm mesh traps would reduce rates of discard and discard mortality given current size limits in this fishery.

The blue crab Callinectes sapidus is a commercially important crustacean species fished along the Atlantic and Gulf of Mexico coastlines. Cull rings on traps are required to allow for egress of sublegal blue crabs in commercial and recreational fisheries in this region. We undertook a study to estimate contact selectivity (retention probability) of traps with different cull-ring sizes fished for male crabs. We estimated retention probability using logistic models and catch data from 38.1-mm square mesh traps, each affixed with one size of cull rings (58.7, 60.3, or 61.9 mm internal diameter), and fished along with control traps (no cull rings). Each experimental trap type displayed relatively steep retention around its l50, the carapace width at which 50% of individuals are selected. The l50 for traps with 58.7-mm cull rings was less than the minimum legal crab size in North Carolina (127 mm carapace width) while the l50 for traps with 60.3-mm or 61.9-mm cull rings was greater than the minimum leg...

Survival estimates were obtained for the Norway lobster, Nephrops norvegicus, retained and escaping from a standard 70 mm mesh size diamond and a modified 55 mm square mesh codend, on board a commercial vessel in fishing grounds off the Portuguese south coast. Ten hauls were carried out, five with each experimental codend, plus three creel sets for the capture of a control group in an adjacent non-trawled area. A total of 571 lobsters were sampled upon arrival on vessel deck, either captured in the codend or retained in the codend cover. In addition, a total of 25 individuals were caught with creels. They were assessed for physical damage and vitality and subsequently placed in cages which were deployed in the same adjacent area for 48 h. Average survival rates were 0.18 and 0.17 for retained individuals and 0.17 and 0.30, for individuals escaping through diamond and square meshes, respectively, and 0.84 for creeled individuals. A discussion is carried out stressing the difficulty in disentangling the influence of the different factors contributing to condition and mortality of individual lobsters.

Unaccounted fishing mortality is recognized as an important determinant in the management of bycatch, and discard survival studies have been conducted in commercial and recreational fisheries around the world. A range of environmental, operational and biological factors affect survival of discarded fish and should be considered when presenting survival estimates. The present study compared discard survival of plaice in the bottom otter trawl mixed fisheries in Skagerrak between (a) seasons, (b) target species and (c) codend designs. In the latter, a horizontally divided codend designed to reduce interactions between spiny Norway lobsters ( Nephrops norvegicus ) and fish during the fishing process was investigated for its capacity to reduce catch damages and improve fish survival. (a) In winter, survival was significantly higher (75%, Confidence Interval (CI): 61–78%) than in summer (44%, CI: 34–61%). (b) When targeting plaice, survival was significantly higher (73%, CI: 63–83%) than when targeting Nephrops (40%, CI: 14–59%) in winter. (c) Using the divided codend, an improvement in discard survival of undersized plaice was possible when targeting Nephrops , but without a significant difference from the 90 mm diamond mesh standard codend (37%, CI: 14–54%) when fish were caught in the 60 mm square mesh lower compartment (61%, CI: 48–73%). In the 120 mm square mesh upper compartment, survival was significantly higher (94% with CI: 81–100%), but few undersized individuals were caught. When targeting plaice, survival rates did not differ between codends.

The growing seal populations of the Baltic have led to more frequent interactions with coastal fisheries. The motivation for seals to interact with fishing gear is high. It provides high densities of fish. A successful means of mitigating the conflict is the pontoon trap. Seal visits here have been frequent. Seals have access to most parts of the trap system including the middle chamber, which is an overhead environment. Concerns have been raised about seals possible entanglement in this specific part of the trap. As a means of keeping seals from entering the middle chamber, two different Seal Exclusion Devices (SEDs) were tested. A diamond mesh SED and a square mesh SED, which was rotated 45°. The aim was to compare the functionality of the different SEDs with respect to seal deterrent abilities and catch composition. The hypothesis tested were (i) that seals would not be able to enter the middle chamber, (ii) that the catch would increase and (iii) that the SED would deter larger fish from swimming into the middle chamber. Catch data and underwater film were collected. Larger salmons were caught in traps equipped with SEDs. The SEDs did not affect the number of caught fish or the total catch per soak day.

Accepted manuscript version, licensed CC BY-NC-ND 4.0. Published version available at https://doi.org/10.1016/j.fishres.2018.03.020. In the laboratory, we investigated which sizes of Nephrops (Nephrops norvegicus) could pass through the meshes of different size and shape to establish a predictive model for the creels size selectivity. Predictions agreed well with the results from experimental fishing, demonstrating the reliability of this simple method. Nephrops minimum target size is 20 mm carapace length in the Mediterranean creel fishery, with some areas having restrictions on the mesh size, minimum being 36 or 40 mm. The model predicts that Nephrops below 28 and 32 mm carapace length would escape from creels with respectively 36 and 40 mm mesh size, implying a suboptimal exploitation pattern. Our method provides easy and quick identification of optimal mesh size and shape without the exhaustive sea trials with various creel designs. It was predicted that a square mesh of 30 mm would better match the desired exploitation pattern. The method could easily be adopted to other species and different creel fisheries, helping to determine optimal mesh matching a prescribed exploitation pattern.

Accepted manuscript version. Published version available at https://doi.org/10.1139/cjfas-2017-0461. Copyright NRC Research Press. Size selectivity of a new sorting section combining a sorting grid and a square mesh panel was tested for haddock (Melanogrammus aeglefinus) in the Barents Sea demersal trawl fishery. Sampling data for a wide size range enabled investigating the selection process for this species in detail, both for the grid and the square mesh panel. Contrary to earlier studies modelling size selectivity for grids and square mesh panels, which assume that the escape behaviour of all sizes of fish is equal, we applied a model that accounted for that haddock of different sizes can show different escape behaviour. Our results demonstrated that this model could describe the experimental data collected better than existing models. Specifically, our results showed that the likelihood for smaller haddock to seek escape through the grid and the square mesh panel was higher than for bigger haddock that still would manage to escape through the devices if they attempted. The new modelling approach presented in this study may be applicable to other species, selection devices and fisheries.

WOS: 000452121100005, The striped red mullet (Mullus surmuletus) is a commercially important demersal species caught by mixed trawl fishing in the Mediterranean Sea. Although it is not among the target species of bottom trawl operations, the striped red mullet is an important species due to its high commercial value in trawl catch composition. The primary target is to catch adult individuals while allowing the immature and juvenile fish to escape for sustainable fisheries using selective fishing gears. Various selectivity studies regarding trawl codends aimed at improving selectivity have been carried out in the past two decades. However, the selectivity sea trials generally require a great deal of work, time, and labor on the deck and are also expensive. Therefore, instead of experimental-based selectivity studies, simulation-based studies (i.e., the FISHSELECT methodology) were recently started to predict the size selectivity of species in bottom trawl fisheries. In this study, sampled individuals of the striped red mullet were used in morphological measurements, fall-through experiments, and simulation phases. Diamond mesh sizes of 40, 44, and 50 mm and a square mesh size of 40 mm of bottom trawl codends were simulated, and the L50 values were calculated as 9.87, 10.75, 12.19, and 12.3 cm for the aforementioned mesh sizes, respectively. Design guides were then created for various mesh sizes and opening angles. The study results were compared with those of previous studies on the red mullet (M. barbatus) that were conducted using the FISHSELECT methodology, and the selectivity results of these two species were found to be similar., Scientific Research Commission of Ege University [16-SUF-008], The research documented in this paper was conducted as part of the Ege University Scientific Research Project No: 16-SUF-008 supported by the The Scientific Research Commission of Ege University and it is also part of MSc thesis of Enis Noyan Kostak. This study was awarded 'Best oral presentation' in the 19th National Fisheries Symposium of Turkey which was organized by Sinop University between 12-15 September 2017.

Many fishing methods result in significant catches of non-target species or individuals that are too small to be retained for economic values or within quota regulations. In the Baltic Sea trap fishery, the major problem is the bycatch of juvenile and non-marketable whitefish (Coregonus maraena) which constitutes a threat to the sustainability of the fishery and a time-consuming problem for the fishers. This study evaluates the effectiveness of a modified fish trap in reducing such bycatch. An encircling selection panel consisting of 50 × 50 mm square mesh netting was installed in a pontoon fish chamber of a salmon/whitefish trap. Comparative fishing was conducted against a control trap without selection panel in the inshore waters of the Bothnian Sea. Comparisons of catch compositions between the traps showed that there was a 72% reduction in juvenile whitefish catch in the experimental trap. The length at 50% retention (30.1 cm) corresponded well to the minimum market size (>30 cm) of whitefish that are desired for the local market. Fishers are advised to use a netting panel of 50 × 50 mm square mesh for their traps to reduce undersized whitefish. The results are important for the sustainability of whitefish stocks in the Baltic Sea.

Many jurisdictions have introduced management regimes prohibiting or limiting discarding, and a key objective of the European Union Common Fisheries Policy is the gradual elimination of discards. One way of reducing the catch of unwanted fish is to use more size-selective gears. Gear-based management options can best be explored using models that predict size selection across a wide range of variables related to gear design. Such a model is developed for haddock (Melanogrammus aeglefinus) through a meta-analysis of 21 trials of codend selection and 19 trials of the combined selection of the codend and a square mesh panel. Individual-haul estimates of the 50% retention length (l50) and the selection range (SR) are related to a set of explanatory variables through a structural model that describes the dual process of panel and codend selection. Codend l50 and SR are positively related to codend mesh size and negatively related to the codend twine diameter. Codend l50 is also negatively related to the number of open meshes around the codend circumference. Panel l50 increases with panel mesh size. The panel contributes more to gear selection as it is moved closer to the codline. The panel is most effective between November and January and least between May and July, periods which broadly coincide with peak and poor haddock condition. The results are illustrated for a typical trawler targeting haddock in the Scottish whitefish sector, and the utility of the model for gear design and legislation is discussed.

WOS: 000413432700005, This study was done on the use of 40 mm square mesh codend in otter trawl, the minimum measure in Mediterranean deep trout fishing in Eastern Mediterranean in accordance with European Union (EU) regulations. Brushtooth lizardfish Saurida undosquamis (Richardson, 1848) is an important catch component in this region. The lumen of the square mesh being always open, makes it easy for the fish to escape. However, the fish can sometimes get stuck in the mesh while trying to escape, which can lead to economical loss in commercial fishing. Effect of shortening the length of codend on the rate of entangling of brushtooth lizardfish was assessed. The 8 m long and 40 mm square mesh codend was shortened to a length of 4 m. It was observed that shortening the net had no negative impact on the selectivity of the gear and in both cases there was an equal amount of loss and dissatisfaction for the fishermen due to the damage caused while taking out the fish that got entangled in the codend meshes., BAP Foundation of Mustafa Kemal University, Authors thank BAP Foundation of Mustafa Kemal University for their financial support.

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 (

This is a pre-copyedited, author-produced version of an article accepted for publication in ICES Journal of Marine Science following peer review. The version of record Sistiaga, M.B., Herrmann, B., Grimaldo, E., Larsen, R.B., Olsen, L., Brinkhof, J. & Tatone, I. (2017). Combination of a sorting grid and a square mesh panel to optimize size selection in the North-East Arctic cod (Gadus morhua) and redfish (Sebastes spp.) trawl fisheries. ICES Journal of Marine Science. 75(3), 1105-1116 is available online at: https://doi.org/10.1093/icesjms/fsx231 Sorting grids and square mesh panels are the two most-applied technical devices to supplement codend size- and species-selection in demer- sal trawls. In the Barents Sea gadoid fishery, the compulsory size-selectivity system comprises a mesh section with a sorting grid followed by a diamond mesh codend. We tested the size-selective performance of a new sorting section that comprised a sorting grid combined with a square mesh panel as a potential alternative for the grid sections currently in use. The new sorting section was shorter and therefore more maneuverable than the existing sorting grid sections. The investigation was carried out on cod and the bycatch species redfish. The grid was found to contribute to the largest proportion of fish release, and the release through the square mesh panel was low. But, the results showed that the grid was successful at guiding fish not escaping through the grid to a second selection process in the panel. However, the square mesh panel did not result on the intended release efficiency except for the smallest sizes of fish, most likely because the guiding angle of the grid and the square meshes in the panel used did not provide a suitable escape path for the desired size range of fish. Therefore, optimizing the mesh size/shape in the panel and/or the guiding angle for the grid potentially could lead to the desired selectivity pattern in the new sort- ing section.

This paper quantifies the effects of a square mesh codend bycatch reduction device (BRD) and turtle excluder device (TED) in the deepwater eastern king prawn (Melicertus plebejus) fishery on the southeast Queensland coast, based upon on a 10-day research charter. The bycatch comprised 224 taxa, mainly gurnards, flatheads, sandpaper fish, hermit and charybdid crabs, mantis shrimps, sand dollars (i.e. sea urchins), dragonets, snipefish, carids and lizardfish. The total mean bycatch rate was comparatively low (1114.0 g ha−1 from the standard diamond mesh codend), mainly because of the relatively deep waters associated with the fishery. When the TED and square mesh codend BRD were used together the total mean bycatch rate was significantly reduced by 29% (796.0 g ha−1) compared to the standard codend, with no significant effect on the prawn catch rate or size frequency distribution. Several bycatch species experienced very large reductions in mean catch rate, due to the square mesh codend, including Graham's conger Gnathophis grahamii (98.2% reduction), dumpling squid Euprymna tasmanica (95.9%), shortsnout threadsail Aulopus curtirostris (90.6%) and sandpaper fish Aulotrachichthys sp. (90.0%). Multidimensional scaling indicated that bycatch assemblages were more affected by latitude and depth than codend type. Based on the results, we recommend that the 47.6 mm square mesh codend be made mandatory in the deepwater eastern king prawn fishery as a highly effective BRD.

Based on size selectivity data for more than 25 000 cod (Gadus morhua) collected during experimental trawl fishing with six different codends, all of which included a square mesh panel, we investigated the effect on cod-release efficiency based on the size of the square mesh panel area, position of the square mesh panel, and stimulation of the escape response. Based on the results, we were able to explain why the BACOMA codend, applied in the Baltic Sea cod directed trawl fishery, releases juvenile cod efficiently, whereas other designs, including a square mesh panel with similar mesh size, are less efficient. Our main findings reveal that the release efficiency of the square mesh panel in the BACOMA codend depends largely on the overlap of the square mesh panel and the catch-accumulation zone in the codend, where cod do not have the option of just drifting further back in the trawl when proximate to the panel. On the contrary, the reduction in panel size by 50% did not significantly affect the release efficiency when the panel overlapped with the catch-accumulation zone. It was possible to stimulate an escape response for cod to achieve a release through a square mesh panel positioned away from the catch-accumulation zone. Our findings demonstrated that this release was as efficient as for a panel mounted in the catch-accumulation zone of the codend. Devices that stimulate behaviour may improve the release efficiency of cod through square mesh panels in other fisheries where this is a problem.

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 109 mm double twine to 129 mm single twine and increasing the mesh size in the upper square mesh panel from 132 to 147 mm, 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 (38 cm) and plaice (25 cm) 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 6.7 cm for cod, and 24.7 and 2.1 cm for plaice. The selection parameters for the most effective modified Bacoma codend were 41.1 and 8.3 cm for cod and 25.2 and 3.9 cm for plaice

Implementing gear-based solutions to reduce bycatch in trawl fisheries can be difficult owing to fishers’ concerns over the fleet-wide applicability of results from discrete, highly controlled experiments associated with the development of such innovations. In New South Wales, Australia, a codend comprising a posterior section made from 35-mm square-shaped mesh (i.e. hung on the bar) was developed and subsequently recommended for partial implementation in a multi-species demersal trawl fishery (i.e. for use when eastern king prawn – Melicertus plebejus – is the primary target species). However, industry concerns over this design have to date prevented its implementation. Here, using direct twin-tow comparisons onboard a subset of the fleet, we quantitatively assessed the performance of the square-mesh codend, relative to the range of diamond-mesh codend designs currently being used, in terms of reductions in bycatch rates and shortfalls in catch rates of retained animals. Generalised linear mixed-effects modelling across all vessels showed that when eastern king prawn was the target species, the square-mesh codend significantly reduced bycatch rates (by ∼48%), but with an accompanying significant shortfall in catch rates of eastern king prawn (∼7%) and a substantial (though not statistically significant) shortfall in catch rates of an important component of the retained byproduct (whiting, Sillago spp., ∼36%). Partitioning of data by vessel revealed that such shortfalls in retained catch were evident for only some vessels, while the square-mesh codend performed as intended for the others. When school prawn (Metapenaeus macleayi) was the target species, substantial shortfalls in catches of school prawn (∼54%) in the 35-mm square-mesh codend confirmed that a codend of a smaller square mesh might be a more appropriate design under those circumstances. Potential strategies to address intra-vessel inconsistencies in performance of the square-mesh codend and thereby facilitate implementation of square-mesh codends in the fishery are discussed.

Link to publishers version: 10.1371/journal.pone.0160354 It is well established that increasing mesh number in the circumference of a diamond-mesh trawl codend can reduce size selection for round fish, whereas selection for flat fish species is unaffected. This effect has also been documented in Mediterranean trawl fisheries. In contrast, no information is available with regard to the effect of increasing mesh number in the circumference of square-mesh codends on the size selection of round fish and flat fish species. A field study was devised to bridge this gap and formulate proposals aimed at improving trawl fishery management. Size selection data were collected for a round fish species, red mullet (Mullus barbatus), and two flat fish species, Mediterranean scaldfish (Arnoglossus laterna) and solenette (Buglossidium luteum). Fishing trials were conducted in the Adriatic Sea (Central Mediterranean) using three square-mesh codends that differed only in mesh number around the circumference. Results demonstrated that increasing the number of meshes from 107 to 213 reduced the 50% retention length (L50) for red mullet by 2.5 cm but did not affect size selection for the two flat fish species. In some fisheries, regulatory provisions regarding the number of meshes in the circumference should therefore be carefully considered both for diamond- and square-mesh codends.

Summary The size selectivity of alternative codends for nylon shrimp and yellow squat lobster was studied off the Chilean coast using the covered codend technique. Various mesh sizes (47 and 63 mm mesh opening) and shapes (diamond and square) in the codends were used. For both species, substituting the DM47 codend with the DM63 codend significantly increased 50% retention length (l50). The change of diamond (DM47) to square mesh (SM47) had a positive effect in size selectivity for nylon shrimp. For yellow squat lobster, no significant effect was observed when changing the diamond (DM63) to square mesh (SM63). Selectivity data were modeled by considering explanatory variables such as ‘codend catch weight’ and ‘vessel’. Increases in the catch significantly reduced the l50 for both species whereas the vessel factor was not significant. Finally, using the length at first maturity as a reference value, the authors concluded that the DM47 codend failed to protect the immature portion of either stock, thus the DM63 codend is recommended.

Summary Differences in size selectivity of commercial (40 mm diamond mesh, 40D), larger mesh (48 mm diamond mesh, 48D), and square mesh codends (40 mm square mesh, 40S) for hake (Merluccius merluccius), greater forkbeard (Phycis blennoides), blackbelly rosefish (Helicolenus dactylopterus dactylopterus) and four-spot megrim (Lepidorhombus boscii) were investigated in the Aegean Sea. The study was conducted using the covered codend method. Data were analysed taking between-haul variations into account. Results showed that changing from a 40D to 48D codend significantly improved mean L50 values, with increases of about 22% for hake, 8% for greater forkbeard, 20% for blackbelly rosefish, and 11% for four-spot megrim (P = 0.000). A change from diamond to square mesh configuration with the same 40 mm netting also significantly increased the mean L50 values, with 45% for hake, 36% for greater forkbeard, and 25% for blackbelly rosefish (P = 0.000). For four-spot megrim the mean L50 value was about 10% lower, but this difference was statistically insignificant (P > 0.05). Despite the increases in L50 values, this study concludes that the selectivity of the 48D and 40S codends is still not sufficient to release fish smaller than length at first maturity for these four species.

In the past, experimental fishing with square mesh codends was conducted with the expectation that this would lead to a better defined size selection indicated by a smaller selection range (SR) of haddock ( Melanogrammus aeglefinus ) and other gadoid species compared to that provided by traditional diamond mesh codends. However, experimental results demonstrated considerable between-haul variations in the selection parameters (L50 and SR). It was speculated that these results could be linked to differences in morphology of individual haddock of the same length. In the present study we assessed which measures of haddock morphology are important for size selection through meshes. We quantified between-individual variation in morphology and used simulation techniques to estimate that this variation can account for less than 28% (range 15–28%) of the SR values found during experimental fishing. By including a realistic range of mesh openings when simulating the fishing process of a square mesh codend, we were able to explain most of the experimental results. Additionally, we used our method to better understand the seasonal variation in size selectivity reported in the literature and to predict the basic selective properties for haddock for other mesh shapes. Finally, we found that the conditions of our model, which describes mesh penetration for haddock based on assessment of morphology, is very similar to the conditions previously applied in the literature to study size selection of haddock in diamond mesh codends.

Codend selectivity for the jack mackerel Trachurus japonicus and the whitefin jack Kaiwarinus equula were evaluated based on data from trouser trawl experiments carried out in the East China Sea, using a test codend of 60 mm diamond mesh and a control codend made of minnow net with a square mesh of 9 mm bar length. Between-haul variations in parameters and the mean selection curves were tested with the catch data in the SELECT approach, and then the model of between-haul variation in the split parameter with the mean selection curve was chosen as the best fit using Akaike’s information criterion model selection. The 50% retention lengths and the selection ranges were 11.4 and 3.36 cm for jack mackerel and 8.83 and 0.93 cm for whitefin jack, respectively. The selection curve for whitefin jack was sharp, whereas that for jack mackerel was relatively wide. As the estimated split parameters indicated, about 80% of the whitefin jack entered the control codend, but 85 and 90% of the jack mackerel entered the control codend in the second and third hauls, respectively. The inequality in the split parameter is discussed from the viewpoint of the animal’s swimming behavior and water movement based on underwater video observations.

The selectivity characteristics of 4 juvenile fish escape panel designs and their utility for the regulation of a multi-species demersal trap fishery were evaluated using a suite of objective socio-economic and biological criteria. The panel designs consisted of a control (type A) which had a hexagonal mesh size which was the same as that of the body of the trap (3.5 cm), a rectangular mesh (type B) which was representative of the current regulation (5.0 x 7.6 cm) and 2 escape panels with square meshes of 7.5 x 7.5 cm (type C) and 10.0 x 10.0 cm (type D). The results demonstrated that there was only a limited reduction in the proportion of juvenile fish and by-catch retained for the existing juvenile escape panel design (type B). Furthermore, as the selectivity characteristics for the key species (Epinephelus coioides and Diagramma pictum) were similar to the control type, the predicted increases in yields, revenues and spawning stock biomass were small by comparison. The escape panel with the largest mesh size (type D) retained the least un-utilized and discarded by-catch. Whilst simulations predicted the highest spawner biomass per recruit, long term yields and revenues for the key species, its use was associated with a dramatic short-term decline in revenues which were 23.3% of the value of the control type. Traps fitted with the type C which had a square mesh of 7.5 x 7.5 cm had the lowest juvenile retention and the highest overall score for all the assessment criteria combined. The study provides an empirical basis for gear regulations for the demersal trap fishery of the Emirate of Abu Dhabi and the wider Arabian Gulf region.

Two sets of trials were conducted, on the west and east coasts of Scotland, to estimate the selectivity of an 80 mm diamond mesh codend fitted with (i) a 35 mm Swedish grid, (ii) a 120 mm square mesh panel (SMP) at 6–9 m from the codline and (iii) a 120 mm SMP at 12–15 m from the codline. The main results can be summarised as follows: • the Swedish grid gear retained all Nephrops • the SMP gears retained between 70 and 88% of Nephrops below about 37 mm and all Nephrops ≥ 40 mm; • the grid gear retained fewer whitefish than the SMP gears. No cod > 34 cm, haddock > 35 cm, whiting > 38 cm and hake > 41 cm were retained by the grid gear; • and the position of the SMP had no significant effect on the retention of Nephrops, cod, haddock, or whiting.

This study was predicated by a recent management proposal to mandate square-mesh codends in an Australian estuarine squid trawl fishery, based on their improvements to the selectivity of penaeid trawls deployed across comparable temporal and spatial scales. The assumption of no impacts of a codend cover on the performance of a squid trawl was validated before it was used to quantify the size and species selection of a conventional codend made from 41-mm diamond-shaped mesh and two new designs made from 29- and 32-mm mesh hung on the bar (i.e. square shaped). Compared to the 41-diamond codend, both square-mesh designs incrementally and significantly reduced the catches of a small legally retained teleost (whitebait Hyperlophus vittatus), but had no significant effect on discarded catches (termed ‘bycatch’). The 32-square codend also significantly increased the sizes at 50% probability of retention for the targeted squid (Luminous Bay squid Loliolus noctiluca and broad squid Photololigo etheridgei), across narrow selection ranges and, because all sizes are retained, consequently reduced their total landed catches. The results support the utility of square-mesh for consistently improving and maintaining lateral openings in codends, but the management of this fishery means that such configurations would result in economic loss, and for the 29- and 32-square codends, no concomitant reduction in bycatch. This study reiterates the need for bycatch issues to be clearly identified and defined on a fishery-specific basis, and prior to the implementation of mitigation measures.

The survival of fish discarded after being caught can be improved by simple gear-based technical measures aimed at reducing discards. We look at the effects of three different codends on the initial health and short-term survival of trawl-caught skate (Rajidae), using a control codend (80 mm diamond mesh used as standard in the fishery) and two experimental codends (100 mm diamond mesh and 100 mm diamond mesh turned on the square). Both experimental nets reduced discarded numbers of fish by ~70%, with no commercial loss. This reduction in discards had an effect in reducing the total weight of the experimental codends by as much as 80%. We also placed 278 skate in onboard holding tanks for 48 h and evaluated the survival rates of fish caught in the different codends. Visual inspection of "health" at time zero was a good indicator of survival, because 86% of skate with a good health score survived (p < 0.01). From a further 1539 skate assessed for health, we show that fish caught in the control codend have the lowest proportional good health score (25%), followed by the 100 mm diamond mesh codend (34%) and the 100 mm square mesh codend (47%). The health of the fish caught is related to codend weight (p = 0.01). We conclude that technical measures aimed at reducing discards have an additional benefit; they indirectly increase discard survival, and the benefits of mitigating discards through by-catch reduction devices may be a more powerful tool in fisheries management than previously thought.

日本海西部海域の沖合底曳網で，現在の菱目網（目合内径 33 mm）コッドエンドと，その前半部の両脇部か天井部あるいは両方に角目網（目合内径 72 あるいは 81 mm）を装着した選別式コッドエンド，菱目網（目合内径 79 mm）コッドエンドを用いて，カバーネット操業実験を行った。標本抽出率を考慮した SELECT 解析によりアカムツとマアナゴに対する選択性曲線を推定した。選択性曲線における曳網間の変動は大きいが，平均的な選択性曲線を比較すると，アカムツは天井部から，またマアナゴは両脇部から抜け出やすい傾向がある。

This study illuminates a range of technological options relevant to present legislation for regulating fish by-catch in a small-meshed Nephrops fishery. The selection of cod, haddock, hake, lemon sole, Nephrops , plaice, saithe, witch, and whiting were evaluated using the twin-trawl technique for: (i) a 90 mm diamond mesh codend (standard codend); (ii) a standard codend with a 120 mm square mesh panel (SMP); and (iii) a standard codend with a 35/80 mm grid mounted in the extension piece to hinder access to the codend for large individuals. We used selection models to estimate selection parameters by species and confidence bands to compare the selective properties of different gear types. For cod, haddock, hake, Nephrops , plaice, and whiting we obtained estimates for all three gear variants, whereas we obtained estimates for lemon sole and witch only with the standard and the SMP codends and for saithe only for the SMP codend. The SMP significantly ( p Nephrops .

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 120 mm mesh cod-ends with (i) 100, 80 and 60 meshes in circumference; (ii) a 35 mm ‘flexi-grid’ mounted in the extension; (iii) a 110 mm ‘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.

Discarding of fish species in the Kattegat-Skagerrak Nephrops directed fisheries remains at high levels. In this work we have tested four sets of codends pair-wise with the catch comparison technique under full commercial conditions to assess their potential in reducing the catch of undersized commercial species, in particular cod. We investigate the position of a 90 mm square-mesh panel (SMP), the effect of increasing the mesh size from 90 to 120 mm in the SMP, the effect of inserting a 90 mm SMP in an 80 mm codend and the effect of increasing the codend mesh size from 90 to 120 mm in a total of 89 hauls. Inserting the SMP 3–6 m from the codline compared to 6–9 m from the codline, reduced catches of cod above the minimum landing size (MLS) and Nephrops above and below the MLS. Increasing the mesh size in the SMP from 90 to 120 mm increased the catch of cod above the MLS in weight with an overall increase of 12% in the revenue. The effect of installing a 90 mm SMP 6–9 m from the codline in a nominal 80 mm codend had no effect on the catch of cod. Increasing the nominal codend mesh size from 90 to 120 mm reduced the catch of all species below the MLS, except monkfish. Catches of Nephrops above the MLS were, however, reduced by approximately one third and the total loss in revenue was 21%.

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.

Rotherham, D., Broadhurst, M. K., Gray, C. A., and Johnson, D. D. 2008. Developing a beam trawl for sampling estuarine fish and crustaceans: assessment of a codend cover and effects of different sizes of mesh in the body and codend. – ICES Journal of Marine Science, 65: 687–696. An experiment was carried out in the Clarence River (New South Wales, Australia) to test the hypotheses that fish and crustacean catches in an experimental beam trawl were affected by a codend cover and the sizes of mesh in the body and codend. The cover had no obvious effects on the catches retained in the codend. Similarly, in comparisons between trawl bodies made from 26- and 41-mm diamond-shaped mesh, there were no differences in the assemblages of fish caught, or in the mean numbers entering the codends. For one species of fish (Acanthopagrus australis), however, there were differences in the proportions caught between the trawl bodies across different size classes. There was also some evidence to suggest that mesh size in the body of the trawl influenced the size selection of school prawns (Metapenaeus macleayi). For most finfish, there were no differences in catches between codends made from 20-mm and from 29-mm mesh hung on the bar (i.e. square-shaped mesh). In contrast, mesh size in the codend was important for the size selectivity of school prawns, with smaller carapace lengths at 50% retention in the 20-mm codend. We conclude that use of a 41-mm mesh in the body and a 20-mm square mesh in the codend of the beam trawl would be appropriate for future sampling with this gear in estuaries of New South Wales. A similar experimental approach to ours is needed in adapting the beam trawl to estuaries in other parts of the world, or in developing other types of research trawl.

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 (L50 ± S.E.: between 7.90 ± 0.97 and 13.76 ± 0.23 mm) and selection ranges (SR: between 2.70 ± 0.18 and 6.71 ± 1.72 mm) 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.

In the continuing drive to reduce discards of juvenile gadoids (whiting, cod, haddock) in the Farn Deeps Nephrops directed fishery in the North Sea, we examine the efficacy of the square-mesh panels (SMP) which are currently fitted to the trawls in that fishery. We find that discards can be further reduced by around 40% through simple modification to these square-mesh panels. While some basic measures to improve their efficacy have been identified, we have not yet described the ‘optimal square-mesh panel’ and thus we indicate areas for further research in this field which may yield further dividends in discard reduction.

[This study investigates the effects of square mesh barriers of various mesh size on escape success of the blue crab, Callinectes sapidus , under laboratory conditions. A total of 743 crabs was caught by beach seine and held in a shore-based aquarium, in circular tanks (O 4 m × 0.9 m) with 0.3 m water depth. Using barriers constructed with square mesh of known size (35, 40, and 45 mm bar length), the proportion of crabs escaping through each mesh size was measured for each half centimetre carapace width (CW) class. A logistic model was fitted to the size frequency data of the retained and escaped blue crabs for each mesh size in the experiment. L 50 for the 35, 40, and 45 mm (bar length) square meshes tested in this study was 8.09 (s.e. 0.117), 9.32 (s.e. 0.088), and 10.56 (s.e. 0.114), respectively. This paper provides the first results for blue crab square mesh selectivity, which could be used as a reference point to indicate the most appropriate mesh sizes to be tested in crab traps during more comprehensive sea trials. Cette etude porte sur l'effet barriere de differentes tailles de maille de filets sur le succes de l'echappement du crabe bleu, Callinectes sapidus , en conditions de laboratoire. Un total de 743 crabes a ete capture a l'aide d'une seine de plage et maintenus dans un aquarium sur la plage, dans des reservoirs circulaires (O 4 m × 0,9 m) de 0,30 m de profondeur d'eau. En utilisant des barrieres construites avec des filets de vides de mailles connues (35, 40, et 45 mm), le pourcentage de crabes s'echappant a travers chaque taille de maille a ete mesure pour chaque classe de largeur de carapace (CW) variant de 0,5 cm. Un modele mathematique a ete ajuste aux donnees de frequence de taille des crabes echappes et non echappes pour chaque vide de maille de l'experimentation. La L 50 pour les mailles de 35, 40 et 45 mm testees au cours de cette etude etait 8,09 (e.s. 0,117), 9,32 (e.s. 0,088), et 10,56 (e.s. 0,114) respectivement. Cette etude fournit les premiers resultats quant a la selectivite des crabes par rapport a la taille de la maille; ils pourraient etre utilises comme reference pour indiquer les tailles de mailles les plus appropriees pour etre testees dans les pieges a crabes au cours d'essais plus pousses en mer. Cette etude porte sur l'effet barriere de differentes tailles de maille de filets sur le succes de l'echappement du crabe bleu, Callinectes sapidus , en conditions de laboratoire. Un total de 743 crabes a ete capture a l'aide d'une seine de plage et maintenus dans un aquarium sur la plage, dans des reservoirs circulaires (O 4 m × 0,9 m) de 0,30 m de profondeur d'eau. En utilisant des barrieres construites avec des filets de vides de mailles connues (35, 40, et 45 mm), le pourcentage de crabes s'echappant a travers chaque taille de maille a ete mesure pour chaque classe de largeur de carapace (CW) variant de 0,5 cm. Un modele mathematique a ete ajuste aux donnees de frequence de taille des crabes echappes et non echappes pour chaque vide de maille de l'experimentation. La L 50 pour les mailles de 35, 40 et 45 mm testees au cours de cette etude etait 8,09 (e.s. 0,117), 9,32 (e.s. 0,088), et 10,56 (e.s. 0,114) respectivement. Cette etude fournit les premiers resultats quant a la selectivite des crabes par rapport a la taille de la maille; ils pourraient etre utilises comme reference pour indiquer les tailles de mailles les plus appropriees pour etre testees dans les pieges a crabes au cours d'essais plus pousses en mer. , This study investigates the effects of square mesh barriers of various mesh size on escape success of the blue crab, Callinectes sapidus , under laboratory conditions. A total of 743 crabs was caught by beach seine and held in a shore-based aquarium, in circular tanks (O 4 m × 0.9 m) with 0.3 m water depth. Using barriers constructed with square mesh of known size (35, 40, and 45 mm bar length), the proportion of crabs escaping through each mesh size was measured for each half centimetre carapace width (CW) class. A logistic model was fitted to the size frequency data of the retained and escaped blue crabs for each mesh size in the experiment. L 50 for the 35, 40, and 45 mm (bar length) square meshes tested in this study was 8.09 (s.e. 0.117), 9.32 (s.e. 0.088), and 10.56 (s.e. 0.114), respectively. This paper provides the first results for blue crab square mesh selectivity, which could be used as a reference point to indicate the most appropriate mesh sizes to be tested in crab traps during more comprehensive sea trials. Cette etude porte sur l'effet barriere de differentes tailles de maille de filets sur le succes de l'echappement du crabe bleu, Callinectes sapidus , en conditions de laboratoire. Un total de 743 crabes a ete capture a l'aide d'une seine de plage et maintenus dans un aquarium sur la plage, dans des reservoirs circulaires (O 4 m × 0,9 m) de 0,30 m de profondeur d'eau. En utilisant des barrieres construites avec des filets de vides de mailles connues (35, 40, et 45 mm), le pourcentage de crabes s'echappant a travers chaque taille de maille a ete mesure pour chaque classe de largeur de carapace (CW) variant de 0,5 cm. Un modele mathematique a ete ajuste aux donnees de frequence de taille des crabes echappes et non echappes pour chaque vide de maille de l'experimentation. La L 50 pour les mailles de 35, 40 et 45 mm testees au cours de cette etude etait 8,09 (e.s. 0,117), 9,32 (e.s. 0,088), et 10,56 (e.s. 0,114) respectivement. Cette etude fournit les premiers resultats quant a la selectivite des crabes par rapport a la taille de la maille; ils pourraient etre utilises comme reference pour indiquer les tailles de mailles les plus appropriees pour etre testees dans les pieges a crabes au cours d'essais plus pousses en mer. Cette etude porte sur l'effet barriere de differentes tailles de maille de filets sur le succes de l'echappement du crabe bleu, Callinectes sapidus , en conditions de laboratoire. Un total de 743 crabes a ete capture a l'aide d'une seine de plage et maintenus dans un aquarium sur la plage, dans des reservoirs circulaires (O 4 m × 0,9 m) de 0,30 m de profondeur d'eau. En utilisant des barrieres construites avec des filets de vides de mailles connues (35, 40, et 45 mm), le pourcentage de crabes s'echappant a travers chaque taille de maille a ete mesure pour chaque classe de largeur de carapace (CW) variant de 0,5 cm. Un modele mathematique a ete ajuste aux donnees de frequence de taille des crabes echappes et non echappes pour chaque vide de maille de l'experimentation. La L 50 pour les mailles de 35, 40 et 45 mm testees au cours de cette etude etait 8,09 (e.s. 0,117), 9,32 (e.s. 0,088), et 10,56 (e.s. 0,114) respectivement. Cette etude fournit les premiers resultats quant a la selectivite des crabes par rapport a la taille de la maille; ils pourraient etre utilises comme reference pour indiquer les tailles de mailles les plus appropriees pour etre testees dans les pieges a crabes au cours d'essais plus pousses en mer. ]

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 100 mm cod-end fitted with a 90 mm mesh square mesh panel between 6.3 and 9.3 m 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

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. © 2014. 109O684 We would like to thank the captain and crew of the commercial trawler “Azim”. Thanks are also extended to students from Faculty of Fisheries in Mersin University for their help during the sea trials. We are also grateful to Michael Pol (Chair of the ICES-FAO Working Group on Fishing Technology and Fish Behaviour) for helpful revision of the manuscript. This study was financed by the Scientific and Technological Research Council of Turkey ( TUBITAK 109O684 ).

Relatively little scientific work has been done to assess the selectivity of square-mesh codends in the highly variable multi-species conditions in the Italian trawl fisheries. Therefore this study was initiated to investigate the effect of using square-mesh and larger diamond-mesh codends on size selectivity of deepwater red shrimp (Aristaeomorpha foliacea) and red mullet (Mullus barbatus), with possible implication in future management measures. Four different codends were used in the sea trials. When size selection estimates are applied for management issues it is not sufficient only to consider the mean size selection parameters. It also needs to consider the effect of between-haul variations in the selection process. In the current study, potential consequences of the between-haul variation on the selection curves have been considered by applying a pooled curve with a double bootstrap approach. The results attained in the present study indicate that the use of 40. mm square-mesh codend results in a 50% retention length (L50) similar to that of the 50. mm diamond-mesh codend, but with a steeper selection range (SR). For red mullet, both 50. mm diamond-mesh and 40. mm square-mesh codends lead to an L50 that is higher than the minimum landing size (MLS, 11. cm). Deepwater red shrimp is not subject to any MLS and may always be landed legally. However, large amounts of juveniles of deepwater red shrimp have been retained in all codends. Council Regulation (EC) No. 1967/2006 called for a discard reduction policy in waters under the jurisdiction of the European Union. As demonstrated in the current paper, to simultaneously improve the size selectivity of fish and shrimp species can be difficult due to large differences in their morphological characteristics, therefore it may question whether more sophisticated alternative of selective devices, such as grids or square-mesh panels, could be implemented in some Mediterranean fisheries. © 2014 Elsevier B.V.