The size selectivity and catch pattern of Trichiurus lepturus in 40 mm diamond and square mesh codends were investigated in this study.A 34 m high opening trawl was used,which is a common design used by fishermen oper...The size selectivity and catch pattern of Trichiurus lepturus in 40 mm diamond and square mesh codends were investigated in this study.A 34 m high opening trawl was used,which is a common design used by fishermen operating along the northwest coast of India,and the cover codend method was employed to determine codend selectivity.Along with the changes in the length at 50%retention rate for Trichiurus lepturus with the usage of the square and diamond mesh codends,indicators to understand the exploitation pattern of this species in the fishery were assessed based on the total number of individuals and on total weight of the catch.The mean selection length increased and discard fraction is reduced when 40 mm square mesh codends are used in place of diamond meshes,however,it is observed that individuals at commercial length are also lost.The results demonstrate that mandatory use of legal mesh sizes alone will be insufficient to aid in the sustainable harvest of this species,given its estimated length at first sexual maturity of 61.2 cm.This is the first study to compare the size selection of this species in 40 mm diamond and square mesh codends along Northwest coast of India.Results of the study will help as a baseline for gear-based regulations in the region.展开更多
The shrimp beam trawl fishery in the northern South China Sea is characterized by high by-catch and poor selectivity problems.Among by-catch species,banded scad(Caranx(Atule)kalla)is economically the most important on...The shrimp beam trawl fishery in the northern South China Sea is characterized by high by-catch and poor selectivity problems.Among by-catch species,banded scad(Caranx(Atule)kalla)is economically the most important one.The aim of this study is to improve the selective properties of codends for banded scad.Size selectivity of 2 traditional diamond mesh codends,with mesh size 25 and 30 mm(defined as D25 and D30,respectively),and 4 new combined square and diamond mesh codends,with25 mm square-mesh and 25 mm diamond-mesh(S25+D25),30 mm square-mesh and 25 mm diamondmesh(S30+D25),35 mm square-mesh and 25 mm diamond-mesh(S35+D25),and 35 mm square-mesh and18 mm diamond-mesh(S35+D18),were tested for banded scad in shrimp beam trawl fishery of the South China Sea.A total of 54 valid hauls were finished using the covered codend method,and 5750 banded scad were caught.Selective parameters were obtained using the logistic equation with the maximum likelihood method,by incorporating the between-haul variation.The results show that the present minimum mesh size for shrimp beam trawl in the South China Sea,25-mm diamond mesh size,is insufficient to release immature banded scad.The S35+D25 codend is proved to be the most eff ective codend to release immature banded scad,and its 50%retention length(L _(50))is larger than the minimum landing size(MLS=63.5 mm)of banded scad.However,the 95%confidence intervals of L _(50) overlap among the three combined mesh codends,the S25+D25,S30+D25 and S35+D25 codend.For a sustainable exploitation of banded scad,larger mesh sizes are suggested to be investigated for the combined mesh codends.展开更多
Flatfish constitute a substantial proportion of the catch in several demersal trawl fisheries across the globe.Therefore,knowledge on how to discriminate between the individuals that are to be captured or released,by ...Flatfish constitute a substantial proportion of the catch in several demersal trawl fisheries across the globe.Therefore,knowledge on how to discriminate between the individuals that are to be captured or released,by size,is important for the sustainability of exploited stocks.Using European plaice(Pleuronectes platessa),flounder(Platichthys flesus),and dab(Limanda limanda)as case-study species,here we investigate how flatfish are selected in trawl codends by experimentally testing the influence of mesh geometry,and its variability,on size selection.Both diamond-mesh and square-mesh codends were tested,as well as three codends where the mesh shape was fixed to minimize its variation during fishing.The most discriminating size selectivity was found with fixed mesh geometry,revealing that variability in mesh openness negatively affects the selectivity of flatfish.Our results further demonstrate that the risk of retaining undersized flatfish tends to increase with increasing mesh opening angle in diamond-mesh codends.Our results also confirm that when fishing with codends of the same nominal mesh size,the square-mesh codend retains significantly higher proportions of undersized flatfish than the traditional diamond-mesh.展开更多
A programmable silicon photonic multiband microwave filter with tunable bandwidths has been demonstrated.The filter has been successfully used to set up a radio-over-fiber link operating in the X-band as a proof of co...A programmable silicon photonic multiband microwave filter with tunable bandwidths has been demonstrated.The filter has been successfully used to set up a radio-over-fiber link operating in the X-band as a proof of concept.For this purpose,we have investigated the programmable photonic integrated circuit comprising 14 tunable balanced Mach–Zehnder interferometers designed into a square mesh architecture and fabricated using CMOS-compatible silicon photonic technology.展开更多
A multiscale foreground detection method was developed to segment moving objects from a sta- tionary background. The algorithm is based on a fixed-mesh-based contour model, which starts at the bounding box of the di...A multiscale foreground detection method was developed to segment moving objects from a sta- tionary background. The algorithm is based on a fixed-mesh-based contour model, which starts at the bounding box of the difference map between an input image and its background and ends at a final contour. An adaptive algorithm was developed to calculate an appropriate energy threshold to control the contours to identify the foreground silhouettes. Experiments show that this method more successfully ignores the nega- tive influence of image noise to obtain an accurate foreground map than other foreground detection algo- rithms. Most shadow pixels are also eliminated by this method.展开更多
文摘The size selectivity and catch pattern of Trichiurus lepturus in 40 mm diamond and square mesh codends were investigated in this study.A 34 m high opening trawl was used,which is a common design used by fishermen operating along the northwest coast of India,and the cover codend method was employed to determine codend selectivity.Along with the changes in the length at 50%retention rate for Trichiurus lepturus with the usage of the square and diamond mesh codends,indicators to understand the exploitation pattern of this species in the fishery were assessed based on the total number of individuals and on total weight of the catch.The mean selection length increased and discard fraction is reduced when 40 mm square mesh codends are used in place of diamond meshes,however,it is observed that individuals at commercial length are also lost.The results demonstrate that mandatory use of legal mesh sizes alone will be insufficient to aid in the sustainable harvest of this species,given its estimated length at first sexual maturity of 61.2 cm.This is the first study to compare the size selection of this species in 40 mm diamond and square mesh codends along Northwest coast of India.Results of the study will help as a baseline for gear-based regulations in the region.
基金Supported by the Special Fund for Agro-scientific Research in the Public Interest(No.201203018)
文摘The shrimp beam trawl fishery in the northern South China Sea is characterized by high by-catch and poor selectivity problems.Among by-catch species,banded scad(Caranx(Atule)kalla)is economically the most important one.The aim of this study is to improve the selective properties of codends for banded scad.Size selectivity of 2 traditional diamond mesh codends,with mesh size 25 and 30 mm(defined as D25 and D30,respectively),and 4 new combined square and diamond mesh codends,with25 mm square-mesh and 25 mm diamond-mesh(S25+D25),30 mm square-mesh and 25 mm diamondmesh(S30+D25),35 mm square-mesh and 25 mm diamond-mesh(S35+D25),and 35 mm square-mesh and18 mm diamond-mesh(S35+D18),were tested for banded scad in shrimp beam trawl fishery of the South China Sea.A total of 54 valid hauls were finished using the covered codend method,and 5750 banded scad were caught.Selective parameters were obtained using the logistic equation with the maximum likelihood method,by incorporating the between-haul variation.The results show that the present minimum mesh size for shrimp beam trawl in the South China Sea,25-mm diamond mesh size,is insufficient to release immature banded scad.The S35+D25 codend is proved to be the most eff ective codend to release immature banded scad,and its 50%retention length(L _(50))is larger than the minimum landing size(MLS=63.5 mm)of banded scad.However,the 95%confidence intervals of L _(50) overlap among the three combined mesh codends,the S25+D25,S30+D25 and S35+D25 codend.For a sustainable exploitation of banded scad,larger mesh sizes are suggested to be investigated for the combined mesh codends.
基金the European Maritime and Fisheries Fund(EMFF)and the Ministry of Food,Agriculture and Fisheries of Denmark(Ministeriet for Fødevarer,Landbrug og Fiskeri)as part of the projects(FastTrack II–Sustainable,cost effective and responsive gear solutions under the landing obligation(33112-P-18-051)and Udvikling af SELEKTive redskaber og teknologier til kommercielle fiskerier(SELEKT)).
文摘Flatfish constitute a substantial proportion of the catch in several demersal trawl fisheries across the globe.Therefore,knowledge on how to discriminate between the individuals that are to be captured or released,by size,is important for the sustainability of exploited stocks.Using European plaice(Pleuronectes platessa),flounder(Platichthys flesus),and dab(Limanda limanda)as case-study species,here we investigate how flatfish are selected in trawl codends by experimentally testing the influence of mesh geometry,and its variability,on size selection.Both diamond-mesh and square-mesh codends were tested,as well as three codends where the mesh shape was fixed to minimize its variation during fishing.The most discriminating size selectivity was found with fixed mesh geometry,revealing that variability in mesh openness negatively affects the selectivity of flatfish.Our results further demonstrate that the risk of retaining undersized flatfish tends to increase with increasing mesh opening angle in diamond-mesh codends.Our results also confirm that when fishing with codends of the same nominal mesh size,the square-mesh codend retains significantly higher proportions of undersized flatfish than the traditional diamond-mesh.
基金Ministry of Electronics and Information Technology(GG-11/15/2020/EMCD)。
文摘A programmable silicon photonic multiband microwave filter with tunable bandwidths has been demonstrated.The filter has been successfully used to set up a radio-over-fiber link operating in the X-band as a proof of concept.For this purpose,we have investigated the programmable photonic integrated circuit comprising 14 tunable balanced Mach–Zehnder interferometers designed into a square mesh architecture and fabricated using CMOS-compatible silicon photonic technology.
文摘A multiscale foreground detection method was developed to segment moving objects from a sta- tionary background. The algorithm is based on a fixed-mesh-based contour model, which starts at the bounding box of the difference map between an input image and its background and ends at a final contour. An adaptive algorithm was developed to calculate an appropriate energy threshold to control the contours to identify the foreground silhouettes. Experiments show that this method more successfully ignores the nega- tive influence of image noise to obtain an accurate foreground map than other foreground detection algo- rithms. Most shadow pixels are also eliminated by this method.
