The original purpose of Vessel Monitoring System(VMS) is for enforcement and control of vessel sailing. With the application of VMS in fishing vessels, more and more population dynamic studies have used VMS data to im...The original purpose of Vessel Monitoring System(VMS) is for enforcement and control of vessel sailing. With the application of VMS in fishing vessels, more and more population dynamic studies have used VMS data to improve the accuracy of fisheries stock assessment. In this paper, we simulated the trawl trajectory under different time intervals using the cubic Hermite spline(c Hs) interpolation method based on the VMS data of 8 single otter trawl vessels(totally 36000 data items) fishing in Zhoushan fishing ground from September 2012 to December 2012, and selected the appropriate time interval. We then determined vessels' activities(fishing or non-fishing) by comparing VMS speed data with the corresponding speeds from logbooks. The results showed that the error of simulated trajectory greatly increased with the increase of time intervals of VMS data when they were longer than 30 minutes. Comparing the speeds from VMS with those from the corresponding logbooks, we found that the vessels' speeds were between 2.5 kn and 5.0 kn in fishing. The c Hs interpolation method is a new choice for improving the accuracy of estimation of sailing trajectory, and the VMS can be used to determine the vessels' activities with the analysis of their trajectories and speeds. Therefore, when the fishery information is limited, VMS can be one of the important data sources for fisheries stock assessment, and more attention should be paid to its construction and application to fisheries stock assessment and management.展开更多
In the present work,the hydrodynamic performance of the double deflector rectangular cambered otter board was studied using wind tunnel experiment,flume tank experiment and numerical simulation.Results showed that the...In the present work,the hydrodynamic performance of the double deflector rectangular cambered otter board was studied using wind tunnel experiment,flume tank experiment and numerical simulation.Results showed that the otter board had a good hydrodynamic performance with the maximum lift-to-drag ratio(K_(MAX) = 3.70).The flow separation occurred when the angle of attack(AOA) was at 45?,which revealed that the double deflector structure of the otter board can delay the flow separation.Numerical simulation results showed a good agreement with experiment ones,and could predict the critical AOA,which showed that it can be used to study the hydrodynamic performance of the otter board with the advantage of flow visualization.However,the drag coefficient in flume tank was much higher than that in wind tunnel,which resulted in a lower lift-to-drag ratio.These may be due to different fluid media between flume tank and wind tunnel,which result in the big difference of the vortexes around the otter board.Given the otter boards are operated in water,it was suggested to apply both flume tank experiment and numerical simulation to study the hydrodynamic performance of otter board.展开更多
In this paper, we tested the hydrodynamic characteristics of a new, double-winged otter board that consists of a forewing, a leading edge slat and a trailing edge flap. Flume experiments were conducted in a circulatin...In this paper, we tested the hydrodynamic characteristics of a new, double-winged otter board that consists of a forewing, a leading edge slat and a trailing edge flap. Flume experiments were conducted in a circulating flume tank by using a model with an aspect ratio(AR) of 0.85 and a horizontal planform area( S) of 0.09 m^2. The results indicated that the critical angle( α_(cr)) of the model was 44°, whereas the maximum lift coefficient( C_(Lmax)) was up to 1.715, and the door efficiency( K) was 1.122. The attack angle( α) ranged from 30° to 48° and from 10° to 46° when the lift coefficient( C_L) and door efficiency( K) were greater than 1.2 and 1.0, respectively. To compare the difference between double-winged otter board and traditional Morgere Polyvalent Ovale, same model of Morgere Polyvalent Ovale was also tested under the same experimental conditions. The critical angle( α_(cr)) and maximum of lift coefficient( C_(Lmax)) of the doublewinged otter board were 37.5% and 14.6% larger than those of the Morgere Polyvalent Ovale. Therefore, we concluded that the novel, double-winged otter board was more suitable for bottom trawling fisheries in the deep water of the Mauretania Sea due to its better hydrodynamic characteristics and stability.展开更多
We used generalized additive models (GAM) to analyze the relationship between spatiotemporal factors and catch, and to estimate the monthly marine fishery yield of single otter trawls in Putuo district of Zhoushan, Ch...We used generalized additive models (GAM) to analyze the relationship between spatiotemporal factors and catch, and to estimate the monthly marine fishery yield of single otter trawls in Putuo district of Zhoushan, China. We used logbooks from five commercial fishing boats and data in government's monthly statistical reports. We developed two GAM models: one included temporal variables (month and hauling time) and spatial variables (longitude and latitude), and another included just two variables, month and the number of fishing boats. Our results suggest that temporal factors explained more of the variability in catch than spatial factors. Furthermore, month explained the majority of variation in catch. Change in spatial distribution of fleet had a temporal component as the boats fished within a relatively small area within the same month, but the area varied among months. The number of boats fishing in each month also explained a large proportion of the variation in catch. Engine power had no effect on catch. The pseudo-coefficients (PCf) of the two GAMs were 0.13 and 0.29 respectively, indicating the both had good fits. The model yielded estimates that were very similar to those in the governmental reports between January to September, with relative estimate errors (REE) of <18%. However, the yields in October and November were significantly underestimated, with REEs of 36% and 27%, respectively.展开更多
Religious wildlife release is prevalent worldwide,especially in Asia countries.It is one of the anthropogenic pathways to cause biological inva-sions.Religious fish release is common on the Qinghai-Tibetan Plateau,yet...Religious wildlife release is prevalent worldwide,especially in Asia countries.It is one of the anthropogenic pathways to cause biological inva-sions.Religious fish release is common on the Qinghai-Tibetan Plateau,yet few studies have assessed the influences of religious fish release on local species.InYushu,a city on the Qinghai-Tibetan Plateau,we interviewedlocal people,conducted fish trap surveys in local rivers,and exam-ined the diet of Eurasian otters Lutra lutra using a fecal DNA metabarcoding approach.We found that fish release started at least in 1980-1990s in Yushu.Tibetan residents released fish in large amounts and released fish were usually exotic commercial fish purchased from market.Despite such long-term and intensive fish release activities,released fish were few in local rivers.On the other hand,Eurasian otters mainly prey on fish and released fish accounted for~20%of relative read abundance of prey DNA in otters'diet,indicating their high preference on released fish.Our study suggested that religious fish release may provide additional food resources for otters,whereas otters,as a top predator in local rivers,may deplete non-native fish once they were released and,therefore,reduce the probability of colonization of released fish,although further studies are required to assess otters'impact.Our study revealed otters'diet in Yushu,providing basic information for local otter management and conservation.Furthermore,it represents a case showing that native predators prey on religious released animals,implying a probable direction forcontrolling invasive species through nativepredator conservation.展开更多
Fishing logbook records the fishing behaviors and other information of fishing vessels.However,the accuracy of the recorded information is often difficult to guarantee due to the misreport and concealment.The fishing ...Fishing logbook records the fishing behaviors and other information of fishing vessels.However,the accuracy of the recorded information is often difficult to guarantee due to the misreport and concealment.The fishing vessel monitoring system(VMS)can monitor and record the navigation information of fishing vessels in real time,and it may be used to improve the accuracy of identifying the state of fishing vessels.If the VMS data and fishing logbook are combined to establish their relationships,then the navigation characteristics and fishing behavior of fishing vessels can be more accurately identified.Therefore,first,a method for determining the state of VMS data points using fishing log data was proposed.Secondly,the relationship between VMS data and the different states of fishing vessels was further explored.Thirdly,the state of the fishing vessel was predicted using VMS data by building machine learning models.The speed,heading,longitude,latitude,and time as features from the VMS data were extracted by matching the VMS and logbook data of three single otter trawl vessels from September 2012 to January 2013,and four machine learning models were established,i.e.,Random Forest(RF),Adaptive Boosting(AdaBoost),K-Nearest Neighbor(KNN),and Gradient Boosting Decision Tree(GBDT)to predict the behavior of fishing vessels.The prediction performances of the models were evaluated by using normalized confusion matrix and receiver operator characteristic curve.Results show that the importance rankings of spatial(longitude and latitude)and time features were higher than those of speed and heading.The prediction performances of the RF and AdaBoost models were higher than those of the KNN and GBDT models.RF model showed the highest prediction performance for fishing state.Meanwhile,AdaBoost model exhibited the highest prediction performance for non-fishing state.This study offered a technical basis for judging the navigation characteristics of fishing vessels,which improved the algorithm for judging the behavior of fishing vessels based on VMS data,enhanced the prediction accuracy,and upgraded the fishery management being more scientific and efficient.展开更多
Vertical cambered V-type otter boards are widely used in large and medium-sized trawlers for their good stability and adaptability to various water layers.However,limited numerical studies on the hydrodynamic performa...Vertical cambered V-type otter boards are widely used in large and medium-sized trawlers for their good stability and adaptability to various water layers.However,limited numerical studies on the hydrodynamic performance and structural strength of this type of otter board have been published.In this study,we established the three-dimensional numerical model of the double-slotted vertical cambered V-type otter board according to its special structure and stress feature.We compare the hydrodynamic performance results of our model with those of previous experiments.Using this model,we analyzed the influence of parameters such as attack angle,aspect ratio,dihedral,and deflector angles on its hydrodynamic performance.Moreover,the structural response characteristics of the otter board under typical working conditions were studied.We believe our results will provide theoretical reference for the structural design and optimization of the vertical cambered V-type otter board.展开更多
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 prox...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.展开更多
In a time of increasing environmental change caused by anthropogenic disturbance,there is a greater need to understand animal adaptations to manmade environments.In this regard,the measurement of stress-related endocr...In a time of increasing environmental change caused by anthropogenic disturbance,there is a greater need to understand animal adaptations to manmade environments.In this regard,the measurement of stress-related endocrine markers provides a useful tool to examine the impact of environmental challenges and the physiological consequences for wildlife occupying such space.The aims of the present study were to validate fecal glucocorticoid metabolite(fGCM)concentrations as a measure of stress using samples from a male African clawless otter(Aonyx capensis;n=1)and to compare fGCM concentrations of otters occurring in a transformed and in 2 natural areas in South Africa.From the 5 different enzyme-immunoassays(EIA)tested,a cortisol and oxoetiocholanolone(measuring 11,17 dioxoandrostanes)EIA revealed the highest response(74%and 48%increase,respectively)30 and 24 hours after a stress event(translocation of a captive individual as part of its rehabilitation prior to release),respectively.For both EIAs,fGCM concentrations were comparable for samples collected up to 3 h post-defecation.Using the cortisol EIA for subsequent analyses,fGCM concentrations of animals from the transformed area(n=20;mean[±SD]:0.468[±0.539]µg/g dry weight[DW])were significantly higher(P=0.013)than those from otters in the natural areas(n=17;0.242[±0.226]µg/g DW).These preliminary results suggest that African clawless otters may have increased adrenocortical activity that could be due to conditions linked to living in a transformed environment.展开更多
In order to study the influence mechanism of structural type and size on the hydrodynamic performance of vertical curved V-type otter board,this paper based on the computational fluid dynamics method,a three-dimension...In order to study the influence mechanism of structural type and size on the hydrodynamic performance of vertical curved V-type otter board,this paper based on the computational fluid dynamics method,a three-dimensional numerical model of vertical curved V-type otter board is established to calculate and analyze its hydrodynamic performance,and the validity of the numerical simulation results is verified by designing and constructing a scaled model for dynamic flume experiments.On this basis,the effects of different structural parameters,such as the deflector angle,camber,and spacing,on the hydrodynamic performance of the vertical curved V-Type otter board are investigated and the optimal structural design scheme is determined.The results demonstrate that single or synchronous changes of the angle,camber,and spacing of the two deflectors have varying degrees of impact on the hydrodynamic performance of the vertical curved V-Type otter board.To improve the expansion effect of the otter board,setting the angle of the deflector A to 40◦and that of the deflector B to 30◦,or setting the camber of deflectors A and B to 18%,or setting the spacing between deflectors A and B to 380 mm and that between the deflector and the main panel to 670 mm can increase the lift coefficient of the vertical curved V-Type otter board to its maximum value.Considering the overall performance of the otter board,when the angle of the deflector A is set to 25◦and that of the deflector B is set to 30◦,or the camber of the deflector A is set to 6% and that of the deflector B is set to 9%,or the spacing between deflectors A and B is set to 340 mm and that between the deflector and the main panel is set to 610 mm,the lift-to-drag ratio of the otter board can be increased to its maximum value.展开更多
Background The impact of changing land-use patterns and associated anthropogenic threats on scale-dependent habitat use of semi-aquatic mustelids in scent-marking and social behaviour can provide important insights in...Background The impact of changing land-use patterns and associated anthropogenic threats on scale-dependent habitat use of semi-aquatic mustelids in scent-marking and social behaviour can provide important insights into the habitat ecology of smooth-coated otters(Lutrogale perspicillata).Methods We sampled 180 stream segments(100–400 m)as spatial replicates of 601-km2 sites to record indirect evidence(i.e.spraints and mass latrine sites)and group sizes of smooth-coated otters along the Tungabhadra Otter Conservation Reserve(TOCR)during the dry season.To quantify habitat,we recorded stream characteristics,riparian vegetation,and anthropogenic disturbances at the local scale,and hydro-environmental characteristics and land uses at the landscape scale.Using Markovian-chain detection and occupancy models,we assessed the multi-scale habitat use of otters in their selection of suitable areas for scent-marking based on repeated presence-absence data on spraint/latrine locations along the TOCR.We further used linear regression techniques to explore relationships between the number of individuals in smooth-coated otter group and hydro-environmental characteristics,spraint/latrine encounter rate,anthropogenic pressure,land cover,topography,and vegetation.Results At the local scale,the probability of spraint deposition and group size decreased with anthropogenic disturbance while the probability of spraint detections decreased with grass cover.At the landscape scale,the probability of otter site use for spraint deposition and group sizes increased in southeast flowing streams.Spraint deposition increased with the proportion of sugarcane fields,whereas in contrast,group size decreased with proportion of sugarcane fields.Conclusions Our findings highlight the first empirical evidence on multi-scale habitat use of a southern Indian population of smooth-coated otters in an inland freshwater ecosystem surrounded by the scrub jungle–agriculture matrix.We suggest that habitat models built from analytical approaches that account for correlated detections can avoid biased predictions when estimating occupancy and detection probability of semi-aquatic or riparian mammal communities with linear distributions.Our findings indicate that human activity can impose constraints on the choice of sites used for spraint deposition and preliminary patterns in otter groups.The study provides some crucial evidence on the need to maintain areas with minimal human interference for sustainability of freshwater reserves.展开更多
基金supported by the National Natural Science Foundation (No. 40801225)the Natural Science Foundation of Zhejiang Province (No. LY13D 010005)Young academic leader climbing program of Zhejiang Province (grant number pd 2013222)
文摘The original purpose of Vessel Monitoring System(VMS) is for enforcement and control of vessel sailing. With the application of VMS in fishing vessels, more and more population dynamic studies have used VMS data to improve the accuracy of fisheries stock assessment. In this paper, we simulated the trawl trajectory under different time intervals using the cubic Hermite spline(c Hs) interpolation method based on the VMS data of 8 single otter trawl vessels(totally 36000 data items) fishing in Zhoushan fishing ground from September 2012 to December 2012, and selected the appropriate time interval. We then determined vessels' activities(fishing or non-fishing) by comparing VMS speed data with the corresponding speeds from logbooks. The results showed that the error of simulated trajectory greatly increased with the increase of time intervals of VMS data when they were longer than 30 minutes. Comparing the speeds from VMS with those from the corresponding logbooks, we found that the vessels' speeds were between 2.5 kn and 5.0 kn in fishing. The c Hs interpolation method is a new choice for improving the accuracy of estimation of sailing trajectory, and the VMS can be used to determine the vessels' activities with the analysis of their trajectories and speeds. Therefore, when the fishery information is limited, VMS can be one of the important data sources for fisheries stock assessment, and more attention should be paid to its construction and application to fisheries stock assessment and management.
基金supported by the National Key Technology R&D Program(No.2013BAD13B03)the Key R&D Project from Science and Technology Department of Zhejiang Province(Nos.2018C02026,2018C02040)+1 种基金the National Natural Science Foundation of China(No.31072246)the Fundamental Research Funds for the Central Universities(No.201564020)
文摘In the present work,the hydrodynamic performance of the double deflector rectangular cambered otter board was studied using wind tunnel experiment,flume tank experiment and numerical simulation.Results showed that the otter board had a good hydrodynamic performance with the maximum lift-to-drag ratio(K_(MAX) = 3.70).The flow separation occurred when the angle of attack(AOA) was at 45?,which revealed that the double deflector structure of the otter board can delay the flow separation.Numerical simulation results showed a good agreement with experiment ones,and could predict the critical AOA,which showed that it can be used to study the hydrodynamic performance of the otter board with the advantage of flow visualization.However,the drag coefficient in flume tank was much higher than that in wind tunnel,which resulted in a lower lift-to-drag ratio.These may be due to different fluid media between flume tank and wind tunnel,which result in the big difference of the vortexes around the otter board.Given the otter boards are operated in water,it was suggested to apply both flume tank experiment and numerical simulation to study the hydrodynamic performance of otter board.
基金Supported by the Technological Research on Reforming Otter Boards of Bottom Trawl in Mauretania and Guinea(China National Fisheries Corporation,CNFC)Technological Research on Transformation and Upgrading of Shrimp Trawl in Sierra Leone(CNFC)Far Sea Fisheries Resources Monitoring and Assessment of South China Sea(No.2013050212)
文摘In this paper, we tested the hydrodynamic characteristics of a new, double-winged otter board that consists of a forewing, a leading edge slat and a trailing edge flap. Flume experiments were conducted in a circulating flume tank by using a model with an aspect ratio(AR) of 0.85 and a horizontal planform area( S) of 0.09 m^2. The results indicated that the critical angle( α_(cr)) of the model was 44°, whereas the maximum lift coefficient( C_(Lmax)) was up to 1.715, and the door efficiency( K) was 1.122. The attack angle( α) ranged from 30° to 48° and from 10° to 46° when the lift coefficient( C_L) and door efficiency( K) were greater than 1.2 and 1.0, respectively. To compare the difference between double-winged otter board and traditional Morgere Polyvalent Ovale, same model of Morgere Polyvalent Ovale was also tested under the same experimental conditions. The critical angle( α_(cr)) and maximum of lift coefficient( C_(Lmax)) of the doublewinged otter board were 37.5% and 14.6% larger than those of the Morgere Polyvalent Ovale. Therefore, we concluded that the novel, double-winged otter board was more suitable for bottom trawling fisheries in the deep water of the Mauretania Sea due to its better hydrodynamic characteristics and stability.
基金Supported by the National Natural Science Foundation for Young Scientists of China (No. 40801225)the Natural Science Foundation of Zhejiang Province (No. Y3090038)
文摘We used generalized additive models (GAM) to analyze the relationship between spatiotemporal factors and catch, and to estimate the monthly marine fishery yield of single otter trawls in Putuo district of Zhoushan, China. We used logbooks from five commercial fishing boats and data in government's monthly statistical reports. We developed two GAM models: one included temporal variables (month and hauling time) and spatial variables (longitude and latitude), and another included just two variables, month and the number of fishing boats. Our results suggest that temporal factors explained more of the variability in catch than spatial factors. Furthermore, month explained the majority of variation in catch. Change in spatial distribution of fleet had a temporal component as the boats fished within a relatively small area within the same month, but the area varied among months. The number of boats fishing in each month also explained a large proportion of the variation in catch. Engine power had no effect on catch. The pseudo-coefficients (PCf) of the two GAMs were 0.13 and 0.29 respectively, indicating the both had good fits. The model yielded estimates that were very similar to those in the governmental reports between January to September, with relative estimate errors (REE) of <18%. However, the yields in October and November were significantly underestimated, with REEs of 36% and 27%, respectively.
基金supported by the National Natural Science Foundation of China(31900372)One Yangtze River Project of the Huatai Securities,and the State Key Laboratory of Biocontrol(Sun Yat-sen University).
文摘Religious wildlife release is prevalent worldwide,especially in Asia countries.It is one of the anthropogenic pathways to cause biological inva-sions.Religious fish release is common on the Qinghai-Tibetan Plateau,yet few studies have assessed the influences of religious fish release on local species.InYushu,a city on the Qinghai-Tibetan Plateau,we interviewedlocal people,conducted fish trap surveys in local rivers,and exam-ined the diet of Eurasian otters Lutra lutra using a fecal DNA metabarcoding approach.We found that fish release started at least in 1980-1990s in Yushu.Tibetan residents released fish in large amounts and released fish were usually exotic commercial fish purchased from market.Despite such long-term and intensive fish release activities,released fish were few in local rivers.On the other hand,Eurasian otters mainly prey on fish and released fish accounted for~20%of relative read abundance of prey DNA in otters'diet,indicating their high preference on released fish.Our study suggested that religious fish release may provide additional food resources for otters,whereas otters,as a top predator in local rivers,may deplete non-native fish once they were released and,therefore,reduce the probability of colonization of released fish,although further studies are required to assess otters'impact.Our study revealed otters'diet in Yushu,providing basic information for local otter management and conservation.Furthermore,it represents a case showing that native predators prey on religious released animals,implying a probable direction forcontrolling invasive species through nativepredator conservation.
基金Supported by the Public Welfare Technology Application Research Project of China(No.LGN21C190009)the Science and Technology Project of Zhoushan Municipality,Zhejiang Province(No.2022C41003)。
文摘Fishing logbook records the fishing behaviors and other information of fishing vessels.However,the accuracy of the recorded information is often difficult to guarantee due to the misreport and concealment.The fishing vessel monitoring system(VMS)can monitor and record the navigation information of fishing vessels in real time,and it may be used to improve the accuracy of identifying the state of fishing vessels.If the VMS data and fishing logbook are combined to establish their relationships,then the navigation characteristics and fishing behavior of fishing vessels can be more accurately identified.Therefore,first,a method for determining the state of VMS data points using fishing log data was proposed.Secondly,the relationship between VMS data and the different states of fishing vessels was further explored.Thirdly,the state of the fishing vessel was predicted using VMS data by building machine learning models.The speed,heading,longitude,latitude,and time as features from the VMS data were extracted by matching the VMS and logbook data of three single otter trawl vessels from September 2012 to January 2013,and four machine learning models were established,i.e.,Random Forest(RF),Adaptive Boosting(AdaBoost),K-Nearest Neighbor(KNN),and Gradient Boosting Decision Tree(GBDT)to predict the behavior of fishing vessels.The prediction performances of the models were evaluated by using normalized confusion matrix and receiver operator characteristic curve.Results show that the importance rankings of spatial(longitude and latitude)and time features were higher than those of speed and heading.The prediction performances of the RF and AdaBoost models were higher than those of the KNN and GBDT models.RF model showed the highest prediction performance for fishing state.Meanwhile,AdaBoost model exhibited the highest prediction performance for non-fishing state.This study offered a technical basis for judging the navigation characteristics of fishing vessels,which improved the algorithm for judging the behavior of fishing vessels based on VMS data,enhanced the prediction accuracy,and upgraded the fishery management being more scientific and efficient.
基金This research was supported by the National Natural Science Foundation of China(31972845)the Open Fund of National Engineering Research Center for Oceanic Fisheries(A1-2801-18-100401-7).
文摘Vertical cambered V-type otter boards are widely used in large and medium-sized trawlers for their good stability and adaptability to various water layers.However,limited numerical studies on the hydrodynamic performance and structural strength of this type of otter board have been published.In this study,we established the three-dimensional numerical model of the double-slotted vertical cambered V-type otter board according to its special structure and stress feature.We compare the hydrodynamic performance results of our model with those of previous experiments.Using this model,we analyzed the influence of parameters such as attack angle,aspect ratio,dihedral,and deflector angles on its hydrodynamic performance.Moreover,the structural response characteristics of the otter board under typical working conditions were studied.We believe our results will provide theoretical reference for the structural design and optimization of the vertical cambered V-type otter board.
基金the National Natural Science Foundation of China(Grant No.31972845).
文摘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.
文摘In a time of increasing environmental change caused by anthropogenic disturbance,there is a greater need to understand animal adaptations to manmade environments.In this regard,the measurement of stress-related endocrine markers provides a useful tool to examine the impact of environmental challenges and the physiological consequences for wildlife occupying such space.The aims of the present study were to validate fecal glucocorticoid metabolite(fGCM)concentrations as a measure of stress using samples from a male African clawless otter(Aonyx capensis;n=1)and to compare fGCM concentrations of otters occurring in a transformed and in 2 natural areas in South Africa.From the 5 different enzyme-immunoassays(EIA)tested,a cortisol and oxoetiocholanolone(measuring 11,17 dioxoandrostanes)EIA revealed the highest response(74%and 48%increase,respectively)30 and 24 hours after a stress event(translocation of a captive individual as part of its rehabilitation prior to release),respectively.For both EIAs,fGCM concentrations were comparable for samples collected up to 3 h post-defecation.Using the cortisol EIA for subsequent analyses,fGCM concentrations of animals from the transformed area(n=20;mean[±SD]:0.468[±0.539]µg/g dry weight[DW])were significantly higher(P=0.013)than those from otters in the natural areas(n=17;0.242[±0.226]µg/g DW).These preliminary results suggest that African clawless otters may have increased adrenocortical activity that could be due to conditions linked to living in a transformed environment.
基金supported by the National Natural Science Foundation of China(Grant No.31972845)the Open Fund of National Ocean Fisheries Engineering and Technology Research Center(Grant No.A1-2006-21-200208).
文摘In order to study the influence mechanism of structural type and size on the hydrodynamic performance of vertical curved V-type otter board,this paper based on the computational fluid dynamics method,a three-dimensional numerical model of vertical curved V-type otter board is established to calculate and analyze its hydrodynamic performance,and the validity of the numerical simulation results is verified by designing and constructing a scaled model for dynamic flume experiments.On this basis,the effects of different structural parameters,such as the deflector angle,camber,and spacing,on the hydrodynamic performance of the vertical curved V-Type otter board are investigated and the optimal structural design scheme is determined.The results demonstrate that single or synchronous changes of the angle,camber,and spacing of the two deflectors have varying degrees of impact on the hydrodynamic performance of the vertical curved V-Type otter board.To improve the expansion effect of the otter board,setting the angle of the deflector A to 40◦and that of the deflector B to 30◦,or setting the camber of deflectors A and B to 18%,or setting the spacing between deflectors A and B to 380 mm and that between the deflector and the main panel to 670 mm can increase the lift coefficient of the vertical curved V-Type otter board to its maximum value.Considering the overall performance of the otter board,when the angle of the deflector A is set to 25◦and that of the deflector B is set to 30◦,or the camber of the deflector A is set to 6% and that of the deflector B is set to 9%,or the spacing between deflectors A and B is set to 340 mm and that between the deflector and the main panel is set to 610 mm,the lift-to-drag ratio of the otter board can be increased to its maximum value.
基金the Science and Engineering Research Board(SERB),Govt.of India,under the“Start-up Research Grant”(Grant Id:SRG/2019/000995)for providing financial support to the fourth author during manuscript preparation
文摘Background The impact of changing land-use patterns and associated anthropogenic threats on scale-dependent habitat use of semi-aquatic mustelids in scent-marking and social behaviour can provide important insights into the habitat ecology of smooth-coated otters(Lutrogale perspicillata).Methods We sampled 180 stream segments(100–400 m)as spatial replicates of 601-km2 sites to record indirect evidence(i.e.spraints and mass latrine sites)and group sizes of smooth-coated otters along the Tungabhadra Otter Conservation Reserve(TOCR)during the dry season.To quantify habitat,we recorded stream characteristics,riparian vegetation,and anthropogenic disturbances at the local scale,and hydro-environmental characteristics and land uses at the landscape scale.Using Markovian-chain detection and occupancy models,we assessed the multi-scale habitat use of otters in their selection of suitable areas for scent-marking based on repeated presence-absence data on spraint/latrine locations along the TOCR.We further used linear regression techniques to explore relationships between the number of individuals in smooth-coated otter group and hydro-environmental characteristics,spraint/latrine encounter rate,anthropogenic pressure,land cover,topography,and vegetation.Results At the local scale,the probability of spraint deposition and group size decreased with anthropogenic disturbance while the probability of spraint detections decreased with grass cover.At the landscape scale,the probability of otter site use for spraint deposition and group sizes increased in southeast flowing streams.Spraint deposition increased with the proportion of sugarcane fields,whereas in contrast,group size decreased with proportion of sugarcane fields.Conclusions Our findings highlight the first empirical evidence on multi-scale habitat use of a southern Indian population of smooth-coated otters in an inland freshwater ecosystem surrounded by the scrub jungle–agriculture matrix.We suggest that habitat models built from analytical approaches that account for correlated detections can avoid biased predictions when estimating occupancy and detection probability of semi-aquatic or riparian mammal communities with linear distributions.Our findings indicate that human activity can impose constraints on the choice of sites used for spraint deposition and preliminary patterns in otter groups.The study provides some crucial evidence on the need to maintain areas with minimal human interference for sustainability of freshwater reserves.
