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Determination of bar spacing of bycatch reduction devices (BRDs) should consider species composition and morphometric characteristics (particularly width) of target species krill and bycatch. This study conducted a scientific investigation of the finfish bycatch in the Antarctic krill (Euphausia superba) trawl fishery by the fishing vessel SHEN LAN in the waters surrounding the South Orkney Islands from December 24, 2022, to February 20, 2023. The results show that scientific observers sampled 676 individuals of finfish bycatch. Of these, 665 were identified to species (17 species from 8 families), while the remaining 11 specimen were juveniles of the Nototheniidae family that could not be identified to the species level. IRI (index of relative importance) calculations showed three dominant (IRI value greater than 1,000) finfish bycatch species (Champsocephalus gunnari, Pseudochaenichthys georgianus, and C. aceratus from the Channichthyidae family) and four important (IRI value between 1,000 and 100) finfish bycatch species (Electrona carlsbergi and Gymnoscopelus nicholsi fromthe Myctophidae family, Gobionotothen gibberifrons from the Nototheniidae family, and Notolepis coatsi from the Paralepididae family). Our study provides morphometric data (particularly body width) that is crucial to model the potential for bycatch reduction by use of bycatch reduction devices (BRDs) and to determine the appropriate candidate bar spacings for BRD sea trials. Predictions suggest that a 10 mm (the maximum body width of krill) bar spacing releases a significant amount of dominant and important bycatch species (93.94% of C. gunnari, 53.99% of P. georgianus, 76.25% of C. aceratus, and 100% of G. gibberifrons). Reduced fishing pressure would reduce the risks to dominant and important bycatch species to make the krill fishery sustainable. We recommend that future BRD sea trials should initially test a 10mmbar spacing. Ifmarked loss of krill is observed, wider spacings (e.g. 15 mm) must be tested. [ABSTRACT FROM AUTHOR]

The silver pomfret fish Pampus candidus (Previously known as Pampus argenteus Euphrasen) was collected from Iraqi marine waters in the northwest Persian Gulf between April and December 2021, using gillnet and demersal trawling. The lengths and weights of fish were recorded, along with data on the initial maturity length, sex ratio, gonadosomatic index (GSI), Dobriyal index, gonad maturation, development cycle, and absolute fecundity rate. The forked length of female individuals varied from 248 to 281mm, whereas that of male individuals ranged from 124 to 194mm. In July, young fish began to appear. Male individuals had a somehow shorter period of sexual maturity compared to female counterparts. Furthermore, it is noted that males tend to be generally less in size compared to females. The length at first maturity female and male was recorded as 203 and 115mm, respectively. The sex ratio tends to increase for males, and there were two peaks in the rise of the gonadosomatic index and Dobriyal's index, which indicate two periods of spawning activity during June and September. Six stages of fish maturity have been identified, with differences in the size of the eggs. They had a long and continuous breeding season that lasted from May to November, and they spawned by releasing eggs in batches. Notably, they have two distinct reproductive periods: The first during May and June and the second during October and November. The relationship of fecundity with weight was found to be more representative than with length. The document mentions that the silver pomfret spawning and nursery areas are adjacent to the Shatt al-Arab discharge area. [ABSTRACT FROM AUTHOR]

Deep-sea coral assemblages are marine biodiversity hot spots. Because of their life history traits, deep-sea corals are highly vulnerable to the impacts of human activities such as fishing. The critically endangered "bamboo coral" Isidella elongata is a key structuring species of deep muddy bottoms that is susceptible to habitat destruction, particularly from trawling. A shallow population of this species was recently discovered by a multibeam and ROV survey offshore of the Asinara Island marine protected area (MPA) (northwestern Sardinia, NW Mediterranean Sea). This vulnerable marine assemblage has been found under healthy conditions at depths ranging from 110 to 298 m. Isidella elongata occurs on a muddy seafloor locally characterised by boulders associated with black coral species (Parantipathes larix and Antipathes dichotoma). The lush colonies of I. elongata seem to be related to natural protection from bottom trawling activity; nevertheless, the presence of lost fishing artisanal nets has been observed in the study area. These structuring species are indicators of vulnerable marine ecosystems, and their conservation is essential for preserving marine biodiversity. Therefore, enlarging the perimeter of the Asinara Island MPA into its deeper western waters is suggested to ensure the protection of these valuable and vulnerable marine ecosystems. [ABSTRACT FROM AUTHOR]

To understand the spatial temporal distribution characteristics of Illex argentinus caught by trawl fishing vessels in the Southwestern Atlantic Ocean and their relationship with key marine environmental factors, this study analyzed the temporal and spatial changes in the fishing ground center of trawl vessels at the ten-day scale from December 2019 to May 2022, combining Chinese trawl fishing log data marine environmental data with satellite remote sensing marine environmental data. Utilizing the Maxent model, ten-day intervals were used as the temporal scale, and ten marine environmental factors, including sea surface temperature, sea surface height, sea surface salinity, chlorophyll concentration, temperature at 50 m and 100 m depth, and the meridional and zonal velocities of ocean currents were quantitatively analyzed to explore the correlation between the spatial distribution of catch and environmental factors. The study reveals that the trawl fishing grounds for Illex argentinus are divided into southern and northern grounds. The southern grounds first appear near 45°20′ S in December, gradually moving southeastward in February and March. The northern grounds do not appear until April, near 42° S in the high seas. On the ten-day time scale, the central fishing grounds of Illex argentinus show significant spatial variability but minor interannual differences. The Maxent model results indicate that sea surface temperature and chlorophyll a concentration are the key environmental factors influencing the spatial and temporal variability of the high seas trawl fishing grounds for most of the time, with high environmental contribution rates during the fishing season. While the range of suitable habitats with an HSI > 0.6 identified by the Maxent model varies significantly between years, a pattern is observed where the range expands at the start and end of the fishing season and contracts during the peak fishing season. This suggests that a more concentrated range of suitable habitats is conducive to accurate predictions of trawl fishing grounds, enabling efficient fishing operations. [ABSTRACT FROM AUTHOR]

Introduction: This study focused on a Chinese Antarctic krill vessel utilising continuous pumping fishing technology. The resistance characteristics of Antarctic krill ships trawling in floating ice areas is of great significance for the navigation and fishing of krill ships in ice areas. Methods: Firstly, MATLAB programming using discrete elements combined with genetic algorithms was used to construct a normal distribution ice flow model. Secondly, a fluid-structure coupling interface is created through the contact between the fluid and the trawl grid, and the displacement and resistance of the trawl grid are evaluated on the shared interface. Finally, the effects of ice density and ship sailing speed on ice resistance were studied. Results and discussion: The results of the calculations results show that ice resistance is positively related to the concentration and speed of floating ice, moreover, there is a special speed point where ice resistance increases rapidly. As the speed increases, the proportion of trawl resistance to the total resistance continues to increase, while the proportion of ice resistance continues to decrease. This paper provides a reference for the navigation and fishing resistance assessment of Antarctic krill ships in floating ice areas. [ABSTRACT FROM AUTHOR]

The sea star Hymenodiscus coronata is the only Mediterranean representative of the deep-sea order Brisingida. In the North-eastern Atlantic Ocean, this species is known to create dense aggregations, while, in the Mediterranean basin, it is generally reported as scattered individuals. Through the analysis of the video footage obtained from an extensive ROV campaign carried out in the northern Strait of Sicily in 2021, over 2850 specimens were counted. The specimens, observed between 310 m and 714 m depth, showed a large variability in size and number of arms. It was noted that 17% of the specimens displayed the peculiar "sail position", with all the arms extended vertically in the water column, possibly increasing the filtration rate. Almost the totality of the individuals was noted on soft bottoms, in accordance with the ecological preferences of the species. The density of H. coronata in each site varied between 0.01 and 0.81 individuals m−2, with the highest densities reported in sites characterized by large muddy areas among rocky outcrops and turbulent hydrodynamic conditions. Although the trawling areas exploited in 2021 did not seem to interfere with the presence of H. coronata in the study area, a precautionary approach should be assumed to protect the largest ever reported Mediterranean aggregation of this poorly known species. [ABSTRACT FROM AUTHOR]

The bamboo-coral Isidella elongata is a key habitat-forming species in the deep Mediterranean Sea. This alcyonacean is listed as an indicator of Vulnerable Marine Ecosystems (VMEs) and as Critically Endangered due to bottom trawling impacts. In this work, a modeling approach was used to predict and map the habitat suitability of I. elongata in the Mediterranean Sea under current environmental conditions. Occurrence data were modeled as a function of environmental parameters. Using climate change scenarios and fishing effort data, the risk of climate change and fisheries impacts on habitat suitability were estimated, and climate refugia were identified. A drastic loss of habitat is predicted, and climate change scenarios suggest a loss of 60% of suitable habitats by 2100. In the central Mediterranean, climate refugia overlapped with active fishing grounds. This study represents the first attempt to identify hot spots for the protection of soft bottom Vulnerable Marine Ecosystems for the entire Mediterranean Sea, and highlights areas most at risk from trawling. This work is relevant to the objectives of the EU Marine Strategy Framework and Maritime Spatial Planning Directives, the Biodiversity Strategy for 2030 regarding priority areas for conservation. [ABSTRACT FROM AUTHOR]

In an attempt to improve the selectivity of Australian fish trawls targeting tiger flathead, Platycephalus richardsoni (≥28 cm total length), the utility of four-seam codends with shortened lastridge ropes and comprising 71-mm meshes turned 90° (T90) hung at the narrowest and widest coherent circumferences was compared against a traditional 91-mm diamond-mesh (T0) codend. Significant effects of codend configuration were limited to an increase in the catches of another commercially important species, latchet, Pterygotrigla polyommata, by both T90 codends, and greater escape of some small tiger flathead from the wide 71-mm T90 codend than from the 91-mm T0 codend. Notwithstanding a need to investigate slightly larger T90 mesh sizes for the fishery, the data imply that unlike most codend configurations, circumference does not negatively affect selection in the stated designs and might not require future regulation. [ABSTRACT FROM AUTHOR]

The overall objective of the study presented in this paper was to evaluate the selectivity properties of three innovative codends in Baltic cod fishing: (1) an ultracross codend of 120 mm square mesh, (2) an ultracross codend with additional devices reducing the speed of water flow—one tarpaulin diffuser and one net confusor of 120 mm mesh, and (3) an ultracross codend with two tarpaulin diffusers and two net confusors of 120 mm mesh. These codends were firstly tested at sea by single trawls and compared to T90 and herring codend trawls, allowing assessment of caught fish mass and dimensions. Additionally, a special divided small-mesh coat for the innovative codends enabled determination of the amount as well as the length and mass of cod escaping from the codend both while the trawling gear was towed and while it was hauled. Further validation of codend selectivity was carried out by a double (twin) bottom trawl set deployed from one cutter in various variants of innovative codends compared to standard ones. The results of the study indicate that the use of an innovative ultracross codend and innovative devices reducing the water flow speed (tarpaulin diffusers and 120 mm net confusors) significantly reduces the number of undersized cod (<35 cm), even down to 1.3%, in the haul and contributes to a reduction in invisible mortal discard. [ABSTRACT FROM AUTHOR]

Trawling the seafloor can disturb carbon that took millennia to accumulate, but the fate of that carbon and its impact on climate and ecosystems remains unknown. Using satellite-inferred fishing events and carbon cycle models, we find that 55-60% of trawling-induced aqueous CO2 is released to the atmosphere over 7-9 years. Using recent estimates of bottom trawling's impact on sedimentary carbon, we found that between 1996-2020 trawling could have released, at the global scale, up to 0.34-0.37 Pg CO2 yr-1 to the atmosphere, and locally altered water pH in some semi-enclosed and heavy trawled seas. Our results suggest that the management of bottom-trawling efforts could be an important climate solution. [ABSTRACT FROM AUTHOR]

The beam trawl is one of the primary operational trawls for Antarctic krill, and its beam provides horizontal expansion support for the trawl net. The hydrodynamic performance of the beam significantly affects the vertical expansion and sinking performance of the trawl, as well as impacts the energy consumption of the fishing vessel. In this study, the beam of the Antarctic krill trawl used on the "Shen Lan" fishing vessel served as a prototype. Three types of beams, cylindrical, airfoil, and elliptical, were designed. The hydrodynamic performances of beams with different shapes at different angles of attack were studied using numerical simulation, and the accuracy of the numerical simulation was validated through the flume test. The results show that the cylindrical beam has a higher drag coefficient and a lower lift coefficient, compared to the airfoil beam and the elliptical beam. Under different angles of attack, the cylindrical beam's drag coefficient is, on average, 49.54% higher than that of the airfoil beam and 59.74% higher than that of the elliptical beam. Its lift coefficient is 87.79% lower than that of the airfoil beam and 85.06% lower than that of the elliptical beam, respectively. At different angles of attack, the hydrodynamic coefficients of the airfoil beam and the elliptical beam are similar, and their trends, with respect to the angle of attack, are generally consistent. The drag coefficients increase with an increasing angle of attack, while the lift coefficients show a trend of initially increasing and then decreasing with an increasing angle of attack. The absolute values of the lift coefficients for the airfoil beam and the elliptical beam both reach their maximum values at an angle of attack of 45°, with values of 0.703 and 0.473, respectively. Compared to the cylindrical beam, the hydrodynamic performances of the airfoil beam and elliptical beam are superior. [ABSTRACT FROM AUTHOR]

Fisheries-independent surveys are a critical tool for monitoring marine populations and communities. However, considerations must be made to account for variable-size-based catchability. The size-specific catchability function is therefore key for estimating size distributions, but often requires extensive data sets or specialized field experiments to determine. We develop a Bayesian model capable of simultaneously estimating both a size-based catchability curve and species-specific size spectrum parameters from trawl data by assuming that individual species size spectra follow a theoretically derived parametric size spectrum model. The resulting model provides a means of estimating catchability and size spectra within an adaptive framework capable of accommodating confounding factors such as vessel power and fish density, potentially allowing for improved biomass and productivity estimates. We demonstrate the application of this model using 15 years of Greenland Halibut (Reinhardtius hippoglossoides) survey data from Nunavut to determine size-specific catchabilities and assess whether the size spectrum of Greenland Halibut has changed across the time series. While size spectrum parameters for this stock were not found to vary, we did find evidence of time-varying catchability parameters across the study period. [ABSTRACT FROM AUTHOR]

Methods for jointly estimating both the size-specific relative retention and absolute retention (retention probability) of two experimental trawl gears are considered. One approach would be to undertake comparative fishing of both gears, from which their comparative catchability can be estimated directly. If comparative catchability can be corrected for differing sampling effort and fishing efficiency of the two gears, then relative retention can be estimated. Furthermore, if a suitable functional form of the absolute retention curve is assumed, then estimates of absolute retention can potentially be obtained. However, these estimated retention curves are seen to have extremely large statistical variability and will not be useful in practice. On the other hand, if the gears are each fished with a non-selective control, then absolute retention can be directly estimated, from which estimates of relative retention can immediately be obtained. However, these estimates of relative retention have greater variability than would be obtained by comparative fishing with the same level of sampling effort. It is shown that a hybrid selectivity design that includes both comparative fishing of the experimental trawls and fishing with a non-selective control provides a more balanced approach. An extensive simulation study is conducted using scenarios based on recently published work on selectivity experiments targeting cod (Gadus Morhua) and hoki/blue grenadier (Macruronus novaezelandiae). [ABSTRACT FROM AUTHOR]

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Measuring the distribution of the fishing effort of trawlers is of great significance for describing marine fishery activities, quantifying fishing systems in terms of marine ecological pressure, and revising the regulations of fishing. The purpose of this paper is to develop an efficient learning algorithm to detect the fishing behavior of trawlers to analyze the distribution of fishing effort. The vessel-monitoring system data of more than 4600 trawlers from September 2019 to April 2023 were used for feature extraction. According to the spatiotemporal information provided by the vessel position data, 11-dimensional features were extracted to form the feature vectors. A Slime Mould Algorithm-optimized Light Gradient-Boosting Machine (SMA-LightGBM) algorithm was proposed to classify the feature vectors to recognize fishing behavior. The presented method showed a remarkable generalization ability and high accuracy, sensitivity, specificity, and Matthews correlation coefficient in the test results, with scores of 98.23%, 98.75%, 97.75%, and 0.9646, respectively. Subsequently, the trained model was used to identify the fishing behavior of trawlers belonging to the coastal provinces of the Bohai Sea and the Yellow Sea in the sea area of 117 °   E ~ 132 °   E , 26 °   N ~ 41 °   N . The fishing effort was calculated and evaluated according to the fishing behavior recognition results. The mean absolute error was 0.3031 kW·h, and the coefficient of determination score was 0.9772. The thermal map of the fishing effort of the trawler was mapped, and the spatiotemporal characteristics were estimated in the region of interest from 2019 to 2023 with a spatial resolution of 1 8 degree × 1 8 degree. This method is an efficient way of analyzing the spatiotemporal characteristics of the fishing effort of trawlers. It provides a quantitative basis for the assessment of fishery resources and can inform fishing policies. [ABSTRACT FROM AUTHOR]

The mantis shrimp Rissoides pallidus (Giesbrecht, 1910) is a rarely reported crustacean species in the central Mediterranean Sea. In December 2020, during a trawl survey off Mazara del Vallo harbor (Strait of Sicily), two specimens of R. pallidus were captured on coastal detritus and coastal terrigenous mud bottoms at about 132 and 152 m depths. Additional information specific to biometrics, bottom types, depth preference, habitats, and geographic distribution of this crustacean species are provided. [ABSTRACT FROM AUTHOR]

The purpose of this study was to comprehend the escape intensity and its influencing factors in Antarctic krill (Euphausia superba) that escaped through large mesh located at the front end of commercial trawl nets. Two pocket nets were employed to collect escaped krill that passed through the mesh opening in the first section (400 mm mesh size, without liner) and second section (16 mm mesh size liner) of the trawl body. The results show that krill escape primarily took place in the first section of the trawl body. Meanwhile, there was almost no krill escape observed in the second section of the trawl body, primarily attributable to the presence of a 16 mm mesh size liner. In terms of body length composition, the average PSI (percentage similarity index) was 67.31 (95% CI: 61.86–72.87) for krill from the pocket net on the larger mesh part and the codend. In addition, the PSI was significantly different (p < 0.05) between the day (60.96, 95% CI: 55.68–66.71) and night (83.62, 95% CI: 76.80–89.46). The escape intensity of krill ranged from 20.83 to 213.13 g·m−2 per ton per hour in the area at the front end of trawl body, with a mean value of 76.52 (95% CI: 55.22–101.09) g·m−2 per ton per hour during the daytime, and 144.66 (95% CI: 110.44–180.03) g·m−2 per ton per hour at night. These results indicate that krill can see and avoid contacting the netting easily during the day, particularly for larger individuals. This provides insight into the design of krill trawls, specifically on the arrangement of liners, which should be integrated from the front part of the trawl body. [ABSTRACT FROM AUTHOR]

The authors have developed a method to estimate the catch efficiency of sampling gear using acoustic information. Since different sampling conditions will cause different sampling results, it is necessary to know more details about catch efficiency to quantitatively catch juvenile fish. In this study, we estimated the catch efficiency of a framed midwater trawl (FMT) for juvenile walleye pollock, and investigated differences in the catch efficiency of the FMT due to various influencing factors. To clarify the effects of different sampling conditions on catch efficiency, we investigated changes in catch efficiency by survey time (daytime and nighttime), net color (black and cyan), and towing speed (2 kt, 3 kt, 4 kt). It was quantitatively shown that the catch efficiency was higher at nighttime than during the daytime, the catch efficiency of black net was higher than that of cyan net, and the catch efficiency was higher at the faster towing speed. Comparing the estimated catch efficiency under different conditions, we found that survey time was the most important influencing factor. [ABSTRACT FROM AUTHOR]

Several Mediterranean fisheries are experiencing flaws in the application of the management system based on input control, including Algeria, where the state of fisheries and stocks remain unclear. This paper focused on the characterization of the catches from bottom trawling by professional fishing vessels in the Mostaganem fishery (West of Algeria). Catch data were collected on board between 2017 and 2020 in two different fishing areas between isobaths 30 and 100 meters in depth. Out of a total of 87 species caught, discards represented a greater variety of species (74) than landings (57). Quantitatively, the landing weights were estimated at 7.8 tons, while the discard weights were lower, accounting for 1.8 tons. Between the two fishing areas, a significant difference was detected in the composition of discards and landings, while for the weights, the two areas were similar. Generally, the Mostaganem fishery is similar to other bottom trawl Mediterranean fisheries both for target and discard species. Otherwise, this research highlighted the existence of an uncontrolled black market, which sustains the practice of illegal, unregulated and unreported fishing, and potentially increases the rate of overexploitation. [ABSTRACT FROM AUTHOR]

Numerical simulation is an important method for calculating the hydrodynamic performance of otter boards used in sea floor trawling. Although such simulations have been explored in prior studies, the effects of the proximity of the otter boards to the seafloor and the plume of upward-drawn sediment during bottom trawling have largely been ignored. In this study, we assessed these factors. The results show that within the angles of attack used during normal operations, the effect of the seafloor bottom boundary of the flow field on the hydrodynamic performance of an otter board is obvious. We found that when the ratio of the distance between the bottom of an otter board and the surface boundary of the flow field to the chord length of the board exceeds 0.4, the influence of the bottom boundary of the flow field on the hydrodynamic performance of the board is negligible. For values of less than 0.4, the seafloor bottom boundary has an increasingly obvious impact on the hydrodynamic performance as this ratio decreases. We also found that the turbid plume of ocean floor sediment raised during bottom trawling has an obvious effect on the lift and resistance coefficients of an otter board at high angles of attack. At low angles, this effect on the lift-to-drag ratio is reversed and less obvious. The simulation results show that the optimal lift-to-drag ratio decreases with an increase in the sediment concentration; however, beyond a certain threshold, an increasing concentration of sediments was not found to have an obvious impact on the lift-to-drag ratio. [ABSTRACT FROM AUTHOR]

The offshore Northern shrimp (Pandalus borealis) bottom trawl fishery in eastern Canada currently uses 22 and 28 mm bar spacing Nordmøre grids to limit bycatch from using small mesh codends. However, a recent rebound of juvenile redfish (Sebastes spp.), that can pass through the grids, has greatly increased bycatch. To address this concern, this study investigated the effectiveness of 17 and 15 mm bar spacing Nordmøre grids in a twin-trawl (paired) configuration against the traditional 22 mm bar spacing grid. Size selectivity analyses showed that the 17 and 15 mm grids resulted in no significant reduction in shrimp catch across all length classes. The 17 mm grid significantly reduced redfish bycatch for all length classes and the 15 mm grid significantly reduced redfish bycatch for individuals larger than 95 mm total length. Less redfish entered the codend with the experimental grids, however, the overlap in width between redfish and Northern shrimp limits the overall sorting efficiency of the grids, leaving some redfish still vulnerable to capture. [ABSTRACT FROM AUTHOR]

Environmental DNA (eDNA) metabarcoding is a method to detect taxa from environmental samples. It is increasingly used for marine biodiversity surveys. As it only requires water collection, eDNA metabarcoding is less invasive than scientific trawling and might be more cost effective. Here, we analysed data from both sampling methods applied in the same scientific survey targeting Northeast Atlantic fish in the Bay of Biscay. We compared the methods regarding the distribution of taxonomic, phylogenetic, and functional diversity. We found that eDNA captured more taxonomic and phylogenetic richness than bottom trawling and more functional richness at the local scale. eDNA was less selective than trawling and detected species in local communities spanning larger phylogenetic and functional breadths, especially as it detected large pelagic species that escaped the trawl, even though trawling detected more flat fish. eDNA indicated differences in fish community composition that were comparable to those based on trawling. However, consistency between abundance estimates provided by eDNA metabarcoding and trawl catches was low, even after accounting for allometric scaling in eDNA production. We conclude that eDNA metabarcoding is a promising method that can complement scientific trawling for multi-component biodiversity monitoring based on presence/absence, but not yet for abundance. [ABSTRACT FROM AUTHOR]

این پژوهش با هدف تعیین میزان و ترکیب گونهای صید ضمنی )صبح و عصر( در صیدگاه ماهی یال اسبی در زمستان سال 1398 در آبهای استان هرمزگان صورت پذیرفت. عملیات صید با تور ترال میان آبی، به مدت یک هفته از ساعت 6 صبح تا 6 عصر انجام شد. میانگین مدتزمان هر تورکشی در مطالعه حاضر4- ساعت و عمق تورکشی بین 58-68 متری ثبت شد. کشتی مجهز به یک تور ترال میان آبی یال اسبی با طناب فوقانی به طول41- متر و اندازه چشمه کشیده 75 میلیمتر در کیسه تور بود. در 21 بار تورکشی، 23 گونه ماهی متعلق به17- خانواده شناسایی شد. ماهی یال اسبی با 100 درصد وقوع در هر تورکشی مشاهده گردید. تعداد صید گونه هدف )یال اسبی( 12719 عدد، به میزان 21423 کیلوگرم با میانگین 1020/14 کیلوگرم و میزان صید ضمنی 1828/28 کیلوگرم با میانگین وزنی 87/10 کیلوگرم در هر ترال کشی بهدست آمد. مقایسه میزان حجم صید گونه هدف )ماهی یال اسبی( و حجم صید گونههای ضمنی در صبح و عصر اختالف معنیداری نشان نداد )0/05

In this study, we developed a semi-pelagic trawl to target redfish (Sebastes spp.) and potentially reduce the capture of bycatch species and seabed impacts in the Gulf of St. Lawrence, Canada. The new trawl used an innovative technique connecting the upper bridles of the trawl to the warps, anterior of the trawl doors, leading to the trawl system being fished off the seabed. Such a technique can be used to match the heights of redfish as they move above the seabed during their diurnal cycle while allowing bycatch species related to the seabed to escape under the trawl. A 1:10 scale model of the trawl was constructed and evaluated in a flume tank to optimize the rigging and then a fullscale trawl was constructed for sea trials. Two field experiments subsequently evaluated the trawl at sea. The first field experiment concentrated on the experimental trawl's operation and video observations of redfish behaviour in the trawl mouth and its effect on trawl entry. The second field experiment concentrated on a small-scale preliminary test on the catch of redfish and bycatch species when the trawl was on or off the seabed. Capture results, though preliminary, indicate that redfish can be targeted commercially with a semi-pelagic trawl, though some redfish will escape under the trawl. Additionally, results suggest that the catches of bycatch species may be reduced. In conclusion, this study suggests that a semi-pelagic trawl could be considered an effective technique to harvest redfish sustainably. [ABSTRACT FROM AUTHOR]

Objective: Large‐scale offshore windfarms are proposed along the U.S. Northeast coast; the first is the Vineyard Wind lease area, which is planned for construction in 2023. During the fall of 2018, an experimental bottom trawl survey in the Vineyard Wind lease area and adjacent control area was conducted to collect preliminary estimates of fish assemblage composition, density, and size distribution. Methods: Initially, a new open cod end design was tested, but poor visibility due to fine substrate rendered the gear inefficient. The survey was completed using the traditional closed‐tow method. Result: The estimates of density and variance enabled a power analysis, which recommended a minimum of 20 tows in the development area and 20 tows in the control area to achieve a 25% chance of detecting a shift in the density of the four most abundant species. Conclusion: These results led to the development of a seasonal bottom trawl survey beginning in 2019 using protocols that align with other shelfwide bottom trawl surveys. Impact statementDesigning environmental impact experiments effectively requires preliminary surveys, funding, and industry partnerships. This research provides the basic information needed to detect a shift in the density of the four most abundant species within a proposed windfarm development area, leading to a full‐scale monitoring program. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the acoustic characteristics of largehead hairtails (Trichiurus japonicus) in the Southern Sea of South Korea from April 2022, using 18, 38, 70, 120, and 200 kHz split-beam echosounders. At two stations, juvenile (preanal length: 3.2 cm–5.8 cm) and immature (preanal length: 13.0 cm–26.0 cm) hairtails were caught by midwater trawling. Juvenile hairtails were distributed in layers without forming schools, while immature hairtails were detected as forming small, clustered schools. The mean volume backscattering strength (MVBS) of immature hairtails was more than 20 dB stronger than that of juvenile hairtails at both the 38 kHz and 120 kHz detection frequencies. Furthermore, the SV of juvenile and immature hairtails was high at 18 kHz and decreased as the frequency increased. We concluded that juvenile and immature hairtails can be distinguished according to their morphological characteristics because the distribution characteristics detected in the echograms differed according to their growth stage. Finally, these findings hold remarkable potential for applications within the field of hairtail identification. Acoustic backscatter information, as presented, offers valuable insights into age determination in this fish species. [ABSTRACT FROM AUTHOR]

There has been an increasing emphasis on reducing the environmental impacts of penaeid trawls by modifying their anterior sections. In one Australian estuary, this approach has culminated in a new generic trawl comprising a slightly smaller mesh size, and steeper and shorter side panels than traditional trawls, combined with a top panel extending forwards of the bottom panel (termed ‘lead-ahead’) and no headline floats. This study sought to investigate if an additional simple, cumulative modification (tickler chain) might help promote adoption of the new trawl, via improved penaeid catches. Six volunteer fishers towing pairs of either the traditional or new trawls in double rigs were asked if an observer could accompany fishing trips, and alternately attach a light tickler chain (∼3 kg) anterior to the ground gear of one trawl. Regardless of the trawl design, the tickler chains significantly increased the catch weights of penaeids, but relatively more so in the new trawls (by 1.11 × vs 1.08 × ). The tickler chains also significantly increased the number and weight of total bycatch in the traditional trawls (by up to 1.22 × ), but not in the new trawls—although there were variable species-specific effects. In terms of total effects, the data support using tickler chains to increase the efficiency of the new trawls and their cumulative benefits, and could be promoted to facilitate broader inter- and intra-fleet adoption.

Globally, interactions between fishing activities and dolphins are cause for concern due to their negative effects on both mammals and fishermen. The recording of acoustic emissions could aid in detecting the presence of dolphins in close proximity to fishing gear, elucidating their behavior, and guiding potential management measures designed to limit this harmful phenomenon. This data descriptor presents a dataset of acoustic recordings (WAV files) collected during interactions between common bottlenose dolphins (Tursiops truncatus) and fishing activities in the Adriatic Sea. This dataset is distinguished by the high complexity of its repertoire, which includes various different typologies of dolphin emission. Specifically, a group of free-ranging dolphins was found to emit frequency-modulated whistles, echolocation clicks, and burst pulse signals, including feeding buzzes. An analysis of signal quality based on the signal-to-noise ratio was conducted to validate the dataset. The signal digital files and corresponding features make this dataset suitable for studying dolphin behavior in order to gain a deeper understanding of their communication and interaction with fishing gear (trawl). Measurement(s) Cetaceans' depredation Measurement Type(s) Vocalization behavior Technology Type(s) Monitoring – Data acquisition Sample Characteristic - Organism Dolphins - Tursiops truncatus Sample Characteristic - Environment Sea Sample Characteristic - Location North-central Adriatic Sea [ABSTRACT FROM AUTHOR]

The current study provides valuable insight into the trawl fishery operating in southern Albanian waters via an integrated approach based on high-frequency onboard monitoring trawl vessels and on-site interviews with local fishers. Multivariate analyses of the composition of species landings or economic revenue revealed groups that, depending on the group, were distinguished by improved fisheries landings and economic efficiency. The majority of the catch consisted of a variety of demersal and small- and medium-sized pelagic species, confirming the Adriatic Sea's multispecies nature. Target species identified in terms of catches and revenue imply a systematic tactic over a long period of time, and incidental catches are equally important in terms of overall group similarity. The identification of target species groups may be useful in assessing the current sampling stratification schemes. [ABSTRACT FROM AUTHOR]

Recently, many password guessing algorithms have been proposed, seriously threatening cyber security. In this paper, we systematically review over thirty methods for password guessing published between 2016 and 2023. First, we introduce a taxonomy for classifying the existing methods into trawling guessing and targeted guessing. Second, we present an extensive benchmark dataset that can assist researchers and practitioners in successive works. Third, we conduct a bibliometric analysis to present trends in this field and cross-citation between reviewed papers. Further, we discuss the open challenges of password guessing in terms of diverse application scenarios, guessing efficiency, and the combination of traditional and deep learning methods. Finally, this review presents future research directions to guide successive research and development of password guessing. [ABSTRACT FROM AUTHOR]

In this study, we determined the biological characteristics and indices of abundance and biomass of two demersal species, turbot and thornback ray, through a scientific trawl survey of Bulgarian Black Sea waters in the autumn of 2020. Turbot is among the most valuable fish species in the Black Sea, and thornback ray is a sensitive cartilaginous species with a significantly declining abundance throughout the Mediterranean region. The stock biomass of turbot was estimated at 1467.6 tons, with a relative abundance of 896,922 individuals, and those of the thornback ray were 1187.9 tons and 519,606 individuals, respectively. Mean turbot abundance, interpolated into 0.5° latitude/longitude grid cells, ranged between 52 and 120 ind·km−2, with a mean biomass of 78.26–238.31 kg·km−2, and for the thornback ray, these indices were within the limits of 0–107 ind·km−2 and 0–219 kg·km−2. The distribution of the different length classes of the two fish species by depth layer was analyzed. Length–weight relationships were estimated based on combined samples of both sexes and separately for female and male individuals, allowing a better understanding of growth patterns. [ABSTRACT FROM AUTHOR]

Mobile bottom contact gear such as trawls is widely considered to have the highest environmental impact of commonly used fishing gears, with concern about impact on benthic communities, bycatch, and carbon footprint frequently highlighted as much higher than other forms of fishing. As a result, the use of such gears has been banned or severely restricted in some countries, and there are many proposals to implement such restrictions elsewhere. In this paper, we review the sustainability of bottom trawling with respect to target-species sustainability, impact on benthic communities, bycatch and discards, carbon footprint from fuel use, and impact on carbon sequestration. We compare the impact to other forms of fishing and other food production systems. We show that bottom-trawl and dredge fisheries have been sustained, and where well managed, stocks are increasing. Benthic sedimentary habitats remain in good condition where fishing pressure is well managed and where VME and species of concern can be protected by spatial management. Bycatch is intrinsically high because of the mixed-species nature of benthic communities. The carbon footprint is on average higher than chicken or pork, but much less than beef, and can be much lower than chicken or pork. The impact on carbon sequestration remains highly uncertain. Overall, the concerns about trawling impacts can be significantly mitigated when existing technical gear and management measures (e.g. gear design changes and spatial controls) are adopted by industry and regulatory bodies and the race-to-fish eliminated. When these management measures are implemented, it appears that bottom trawling would have a lower environmental impact than livestock or fed aquaculture, which would likely replace trawl-caught fish if trawling was banned. A total of 83 bottom-trawl fisheries are currently certified by the Marine Stewardship Council, which is the most widely accepted measure of overall sustainability. [ABSTRACT FROM AUTHOR]

Acoustic-trawl surveys are widely used to measure the abundance and distribution of pelagic fish. The echo integration method used in these surveys requires estimates of the target strength (TS, dB re 1 m2) of acoustic scatterers. Here, we present a new automated method to estimate TS from a large volume of previously collected acoustic survey data recorded near trawl sites. By applying a series of selection and filtering methods to echosounder data, single echo measurements representative of fish encountered during surveys can be objectively and reliably isolated from existing survey data. We applied this method to 30 surveys of walleye pollock (Gadus chalcogrammus) conducted in Alaska from 2007 to 2019 and estimated a new length-to-TS relationship. The resulting relationship (⁠|$TS = 20.0 \cdot {\log _{10}}\,L - 66.0$|⁠) was largely consistent with previous in situ estimates made during dedicated, mostly nighttime TS collection events. Analysis of this sizeable data set (n  = 142) indicates that increased fish depth, lower ambient temperature, and summer months may increase pollock TS. The application of a new TS model incorporating these environmental covariates to historic surveys resulted in -16 to +21% changes in abundance relative to the model without environmental covariates. This study indicates that useful TS measurements can be uncovered from existing datasets. [ABSTRACT FROM AUTHOR]

Marine resources exploitation through bottom trawling affects marine ecosystems; thus, management should consider the presence of sensitive species as ecosystem health indicators. Epibenthic organisms such as sea pens are widely used to assess benthic conditions, as their populations are declining where trawling is intense. The Pomo/Jabuka Pits fishing ground in the Adriatic Sea, subject to various management measures over the years, is a nursery for European hake and hosts a small, but dense, population of Norway lobster and a remarkable abundance of pink shrimp. The sea pen Funiculina quadrangularis shares its habitat (sandy-muddy bottoms) with these crustaceans. Through UnderWater TeleVision surveys conducted from 2012 to 2019, F. quadrangularis abundance and distribution were quantified in relation to changes in the spatiotemporal distribution of fishing efforts. The average density (n/m2) of colonies was calculated for three periods: BEFORE implementation of measures (before 1 July 2015), during an INTERMEDIATE period in which limitations changed (2 July 2015 to 31 August 2017), and AFTER the implementation of a Fishery Restricted Area (from 1 September 2017). F. quadrangularis revealed an increase in density where fisheries were closed, even after a short period. This showed how management measures can positively influence epibenthic communities and that sea pens can be indicators of impact and/or recovery of habitats. [ABSTRACT FROM AUTHOR]

Marine Protected Areas require comprehensive monitoring to ensure objectives are achieved; however, monitoring natural ecosystems at scale is challenged by the biodiversity it aims to measure. Environmental DNA (eDNA) metabarcoding holds promise to address this monitoring challenge. We conducted paired sampling at 54 sites for fish and invertebrate assemblages in the Northwest Atlantic using groundfish trawls and eDNA metabarcoding of benthic seawater using four genetic markers (12S rRNA, 16S rRNA, 18S rRNA , and CO1). Compared to trawling, eDNA detected similar patterns of species turnover, larger estimates of gamma diversity, and smaller estimates of alpha diversity. A total of 63.6% (42/66) of fish species captured by trawling were detected by eDNA, along with an additional 26 species. Of the 24 missed detections by eDNA, 12 were inevitable as they lacked reference sequences. Excluding taxa assigned to higher than species level and those without a species name, 23.6% (17/72) of invertebrate species captured by trawling were detected by CO1, which detected an additional 98 species. We demonstrate that eDNA is capable of detecting patterns of community assemblage and species turnover in an offshore environment, emphasizing its strong potential for a non-invasive, comprehensive, and scalable tool for biodiversity monitoring supporting marine conservation programmes. [ABSTRACT FROM AUTHOR]

Spatial restrictions to human activities such as bottom trawling are increasingly used to improve the ecological condition of disturbed habitats. Such management interventions typically have socio-economic consequences, which creates a challenge for those making decisions about which activities should be restricted and where restrictions should apply. We present an approach for predicting the effects of fisheries management scenarios in spatially delimited marine areas and ranking them—using a loss function—according to how well they achieve desired outcomes across a set of ecological and socio-economic indicators. This approach is demonstrated by simulating alternative fishing gear restrictions and zoning options within a hypothetical marine protected area (MPA). Relative benthic status (RBS; an indicator of ecological condition) and relative catch value (RCV; an indicator of potential economic cost) were estimated for the baseline environment and 21 potential management scenarios. The rank order depended on which indicator was prioritized (i.e. whether RBS or RCV was given greater weighting in the loss function), with the top-ranked scenarios in each case involving considerably different management measures. The methods presented can be applied anywhere using locally or strategically relevant indicators to help identify spatial fisheries management measures that minimize ecological and socio-economic trade-offs. [ABSTRACT FROM AUTHOR]

The structure of fishnet knots has been simplified in previous studies to facilitate the construction of numerical equations of the fishnet structure. This leads to errors in the dynamic analysis of the trawl mesh structure with water flow. In this study, the finite element method was used to analyze the interaction of the trawl mesh structure with the solid object in a dynamic explicit environment. At the same time, design variables were optimized through impact assessment and the displacement of grid cells. The results show that the polyamide (PA) material, a 0.4 mm cross-section, and a 25 mm mesh size are the optimal choices. When the displacement speed of the solid body increased, the displacement and collision values of the mesh structure tended to increase gradually along the quadratic curve. Confirmation tests performed on the tensile tester machine showed a good load-carrying capacity of up to 1280 MPa for trawl mesh structures using the PA material. The characteristic curve for the stress of the trawl mesh structure is shown through the higher-order curve. [ABSTRACT FROM AUTHOR]

Experiments were conducted to assess the selectivity of diamond mesh codends in capturing largehead hairtail (Trichiurus lepturus) in the demersal trawl fishery of the Beibu Gulf, located in the South China Sea. The selectivity experiments involved four codends with different mesh sizes (30, 35, 40, and 45 mm), and the covered codend method was employed. Catch data were analyzed using the maximum likelihood method, with both Logistic and Richards curves fitted to the data, and the abundance–biomass comparison (ABC) curve method was used to analyze the impact of codend on fishery resources. Model deviance was compared with the degree of freedom to choose the best fit curve. The Logistic curves gave a better fit for the codends with 30 and 40 mm mesh sizes, while the Richards curves had a better fit for the codends with 35 and 45 mm mesh sizes, respectively. The 50% retention lengths (L50) and selection ranges (SR) were determined for 30 mm (L50: 11.40 cm; SR: 3.81 cm), 35 mm (L50: 11.65 cm; SR: 3.98 cm), 40 mm (L50: 12.92 cm; SR: 5.30 cm), and 45 mm (L50: 13.28 cm; SR: 4.14 cm) mesh codends. The results indicated that the present minimum mesh size, 40 mm diamond mesh, did not match with minimum landing size of largerhead hairtail, 190 mm anal. length. Based on the observed linear relationship between L50 and mesh opening, it was determined that the diamond mesh codend should be adjusted to a larger mesh opening of approximately 72.47 mm in order to achieve an L50 value of 190 mm. The ABC curve characteristics indicate that the fish community structure in the Beibu Gulf in the South China Sea is in a severely disturbed state. This study suggests that the square mesh codend and T90 codend (diamond mesh netting turned by 90 degrees) should be tested and compared with the diamond mesh codend, to obtain the optimal configuration and mesh size of the codend for demersal trawl fishery in the Beibu Gulf in the South China Sea. [ABSTRACT FROM AUTHOR]

In order to optimize the size selectivity of demersal trawl targeting Banded Scad, Alepes djedaba, in the South China Sea (SCS), we tested and compared the selective properties of four experimental codends. These codends included two diamond-mesh codends (T0 codends) with different mesh openings (30 and 35 mm), and two T90 codends (the netting was turned by 90 degrees) with the relatively same mesh opening. The results demonstrated that the T0_30 codend (diamond-mesh codend with 30-mm mesh opening) presented the best size selectivity and is a potential choice to harvest Banded Scad in the studied area among the codends tested. Although applying the T0_35 or T90_30 codend might obtain a little improvement in size selectivity, the loss of marketable-size individuals could be a compromise. Considering the results in our study and those of previous studies, we recommend that the T0_30 codend should be mandated in the fisheries management regulation of trawl fisheries targeting Banded Scad in the SCS. [ABSTRACT FROM AUTHOR]

The North-Western Black Sea shelf is extremely vulnerable to disturbances of its habitats and ecosystems. In the past 10 years, this area has become targeted by beam trawl fisheries for the invasive gastropod Rapana venosa (Valenciennes, 1846), with a potentially destructive impact on the area's soft bottoms. Not many studies have been performed in the region, and most investigations have focused on gear selectivity and by-catch rates. In this context, our novel research aimed, on the one hand, to assess and quantify the actual impact of beam trawling and, on the other hand, to propose effective spatial/temporal management measures for a sustainable zonation of the North-Western Black Sea shelf (marine zone of the Danube Delta Biosphere Reserve). The methodology used integrated beam trawl catch dynamics information, VMS data, geophysical investigations, and macrozoobenthos sampling. Our findings show that beam trawling activities can cause changes in the benthic habitat structure (lower number of taxa, lower values of ecological indicators, and an overall non-GES status). Further in-depth investigations are needed to underpin the ecosystem-based management of this marine protected area (MPA), aiming to allow the recovery of the affected benthic habitats, by alternating defined areas undergoing fishing with biological recovery polygons. [ABSTRACT FROM AUTHOR]