Identification of navigation characteristics of single otter trawl vessel using four machine learning models

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.

Analyses of Trawling Track and Fishing Activity Based on the Data of Vessel Monitoring System(VMS): A Case Study of the Single Otter Trawl Vessels in the Zhoushan Fishing Ground

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.

A Comparative Study on Hydrodynamic Performance of Double Deflector Rectangular Cambered Otter Board

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.

Spatiotemporal factors affecting fish harvest and their use in estimating the monthly yield of single otter trawls in Putuo district of Zhoushan, China

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.

Hydrodynamic characteristics of the double-winged otter board in the deep waters of the Mauritanian Sea

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.

Eurasian otters prefer to prey on religious released nonnative fish on the Qinghai-Tibetan Plateau

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.

Effect of structural parameters on the hydrodynamic performance of vertical curved V-Type otter board

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.

Influence of bottom and sand curtain on hydrodynamic performance of otter boards

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.

立式双曲面网板水动力性能优化研究

为研究结构型式及尺寸对立式双曲面网板水动力性能的影响机理,基于计算流体力学方法,建立立式双曲面网板三维数值模型,计算分析其水动力性能,并通过设计制作缩比模型开展动水槽试验,验证数值结果的有效性。开展曲面板弯曲度、弯曲度位置、支撑板间距等不同结构参数对立式双曲面网板水动力性能的影响规律研究,以探究最优化的结构设计方案。研究结果表明:曲面板弯曲度的同步改变和单一改变均会对立式双曲面网板的水动力性能产生不同程度的影响。如果只考虑扩张效果,曲面板A、B的弯曲度均设置为20%左右,或曲面板A弯曲度设置为15%、曲面板B弯曲度设置为25%左右,均可在一定范围内将立式双曲面网板的最大升力系数提高到最大值;但从网板综合性能考虑,后一方案可获得更高的最大升阻比。当曲面板弯曲度位置同步设置为50%时,网板升力系数可达到最大值,此时扩张效果最佳,而当曲面板弯曲度位置同步设置为20%时,最大升阻比达到峰值,网板综合性能相对更好。支撑板间距对立式双曲面网板水动力性能的影响不明显,将支撑板间距设置为420 mm左右,可在小冲角范围内提升其最大升阻比。

基于流固耦合算法的不同材料网板水动力试验

拖网网板的水动力模型试验结果会因加工工艺、加工方式、加工材料和试验条件等多种因素出现不同程度的试验偏差。为探究网板模型不同加工材料对水动力试验的影响机理,选取双开缝矩形曲面网板为研究对象,基于流固耦合算法结合动水槽模型试验,分析丙烯腈-丁二烯-苯乙烯共聚物(ABS)、聚丙烯(PP)、聚氯乙烯(PVC)3种3D打印材料网板模型与传统钢质网板模型的结构响应差异及其对水动力试验的影响规律。结果显示:采用传统金属材料(钢)与非金属材料(ABS)加工的网板模型在结构响应及水动力性能方面均具有显著差异,且随冲角和流速的增加,网板模型的最大变形量增加,进而导致升/阻力系数差异也进一步增加;PVC材料因其弹性模量较大、刚性较强,结构响应与金属材料较为接近,因而对水动力试验结果影响较小。基于上述结果,开展网板水动力模型试验时,可选用PVC作为3D打印材料,但需确保模型制作精度,避免模型材料对水动力试验结果精度的影响。

基于微卫星的欧亚水獭个体识别和遗传多样性

种群数量和遗传多样性是保护濒危物种所需的基础信息。欧亚水獭(Lutra lutra)属于国家二级保护动物,曾经在我国分布广泛,但在20世纪经历了大规模的种群数量下降和分布区缩减。欧亚水獭相关研究十分缺乏,种群数量调查和遗传多样性等基础研究亟待开展。本研究采用非损伤性取样法,于2019—2020年在青海省玉树藏族自治州玉树市和四川省广元市青川县的主要河流共采集270个欧亚水獭粪便样品并进行DNA提取,基于9个微卫星位点和SRY基因分子标记进行个体识别和性别鉴定,进而使用非损伤性标志重捕法Capwire估计两地水獭的种群数量,并基于微卫星分型数据评估两个种群的遗传多样性。最终共有67个粪便样品(24.8%)成功分型7~9个微卫星位点并用于个体识别,共识别出玉树市10个个体、青川县30个个体,雌雄性比分别为4:5、15:14,两地各有1个个体未成功鉴定性别。估计研究区域内玉树的水獭种群数量为13只(95%置信区间:7~21只)、青川县的水獭种群数量为75只(95%置信区间:59~133只)。玉树、青川种群的平均观测杂合度H_(O)分别为0.680、0.664,平均期望杂合度HE分别为0.611、0.658,表明两个水獭种群均具有中等的微卫星遗传多样性。玉树、青川种群的平均F_(ST)为0.238,平均近亲繁殖系数F_(IS)分别为-0.121、-0.010,表明两个水獭种群之间分化显著,且种群内近交程度低。本研究是我国大陆地区基于粪便DNA对欧亚水獭进行种群数量估计和遗传多样性评估,可为我国水獭的保护提供重要的基础信息。

基于CFD的多叶可控网板水动力特性及压力流场研究

传统网板通过改变曳纲长度和拖速控制作业深度,通过改变网板与曳纲和手纲的固结点位置调整作业姿态,操作复杂。为了给可控变水层网板的设计研究提供科学参考,设计了一款多叶可控网板,通过数值模拟仿真计算流体动力学(Computational fluid dynamics,CFD)探究其不同部位(上端、下端)叶片的转动方向和转动角度(-40°~40°)对其水动力性能的变化影响。结果显示:1)叶片闭合时,多叶可控网板的升力系数在20°冲角时达到最大值0.88;其升阻比在5°冲角时达到最大值8.85。2)0°冲角时,网板两端叶片朝负方向转动,升力逐渐减小至0,并在转角为-20°时,升力变为相反方向;两端叶片朝正方向转动,升力系数先增大后减小,在转角为20°时达到最大值0.32;升阻比随叶片冲角的增加而减小。3)20°冲角时,网板两端叶片朝正方向转动,升力系数不断减小;叶片朝负方向转动,升力系数先增大后减小,在-10°转角时达到最大值1.05;升阻比在-20°转角时达到最大值5.25。4)两组冲角下,两端叶片分别朝正方向转动,Z轴分力系数均先增大后减小。

Hydrodynamic performance and structural response characteristics of the double-slotted vertical cambered V-Type otter board

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.

Monitoring the effects of land transformation on African clawless otters(Aonyx capensis)using fecal glucocorticoid metabolite concentrations as a measure of stress

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.

海獭Sea Otter "毁三观"的最强反差

提起海獭,满脑子都是各种萌出一脸血的画面,简直与任何负面词汇都联系不上。可很多时候现实真相都会让我们三观坍塌,一脸人畜无害、漂在水上连睡觉都要手拉手的海獭,竟然还有暗黑残暴的一面……

完达山东部欧亚水獭种群数量及出现频次影响因素

水獭作为淡水生态系统健康的指示种和旗舰物种,在维持水生生态系统平衡与稳定中发挥着重要作用。然而目前对于完达山东部地区水獭种群数量、分布及其生境选择的影响因素的研究较为匮乏,严重影响了对该物种的野外保护与管理工作。于2021年12月至2022年4月冬季河流封冻期,采用沿河随机样线调查和红外相机监测相结合的方法对完达山东部地区8条主河和23条支流内的欧亚水獭(Lutra lutra)种群数量、分布现状进行了调查,并利用广义可加模型探究水獭出现频次与环境因子的关系。研究结果表明:(1)欧亚水獭在完达山东部水獭种群数量为571—661只,水獭种群密度为沿河(0.5559±0.2898)只/km,呈现中间高,四周低的趋势;(2)环境因子对水獭出现频次影响分析表明,河流深度、距农田距离、距居民区距离和距道路距离是影响水獭出现频次的关键因素。水獭出现频次与河流深度(0—40 cm)呈线性正相关,当河流深度达到40—50 cm时,水獭出现频次最高,之后随着河流深度的增加,出现频次降低;水獭出现频次与距农田距离(0—1.5 km)呈非线性正相关,在距农田距离为1.5—2 km范围内,水獭出现频次最高,之后降低;水獭出现频次与距居民区距离呈线性正相关;水獭出现频次与距道路距离呈非线性关系,当距离>7 km时,二者之间呈现为正相关,反之呈现为负相关。因此,水獭选择栖息地偏向于河流深(40—50 cm),远离农田(1.5—2 km)、居民区和道路(>7 km)的水域。研究为完达山东部欧亚水獭物种保护提供了基础数据和理论依据,建议通过河岸土地覆盖类型的管理、在河岸周围建立森林缓冲区及加强水獭保护宣传力度等措施实现对水獭物种及其栖息地的维持和保护。

基于CFD的拖网网板模型参数对水动力试验的影响研究

拖网网板的水动力模型试验结果经常会因雷诺数、模型尺度等各种试验因素出现不同程度的结果偏差。为研究模型参数对拖网网板水动力试验的影响机理,选取立式V型曲面网板为研究对象,基于水槽模型试验结合计算流体力学数值模拟方法,对比分析其水动力性能及流场分布,探究模型尺度比、板面厚度及模型材料等参数对其水动力试验结果的影响。结果显示:模型尺度比变化对网板升/阻力系数曲线形状无显著影响,但模型尺度缩小过多(20∶1)将导致升力系数在小冲角(α<30°)时偏差明显;模型板面厚度增加会导致升力系数在大冲角(α>30°)下的显著降低,而对阻力系数的影响则主要反映在小冲角(α<30°)时;非金属材料模型由于刚性不足,在水槽模型试验过程中容易因受力后产生一定位移与变形而引起试验结果的偏差。基于上述结果,设计网板水动力模型试验时,应使得模型尺度尽可能大,减小模型尺度对试验结果精度的影响;可适当增加板面厚度以提高模型结构稳定性,增厚范围不宜超过2倍。

喜马拉雅旱獭高原低氧适应性的研究性进展

喜马拉雅旱獭是生活在青藏高原(海拔2700~4500 m)地区的特有野生动物物种,其广泛分布在青海省高山草甸草原、高山草原山地环境中,经过数千年的高原低氧适应,所具有的生物学特性在生物医学领域得到了广泛的应用。随着分子生物技术的进步,研究学者开始从整体水平逐渐向分子水平进行喜马拉雅旱獭的相关研究,认识逐渐加深。因此,喜马拉雅旱獭被视为研究高原低氧适应性物种的理想模型之一。旨在系统探讨喜马拉雅旱獭的低氧适应性机制,包括血液学特征以及低氧适应相关基因。通过这样的研究,可以提高对高原低氧适应性动物的认知水平,增深对高原低氧适应性发生机制的了解,并为高原疾病的预防和治疗奠定基础。

2种立式曲面缝翼式网板水动力学性能的试验研究

为通过调节导流翼偏角优化网板的水动力学性能,利用水槽模型试验测得2种立式曲面缝翼式网板各3种导流翼偏角状态下的升力系数（CL）、阻力系数（CD）和升阻比（K）。结果表明：1）对单缝翼立式曲面网板,冲角为20°~35°时,随着导流翼偏角的增大,网板升力系数和阻力系数均呈下降趋势。该冲角范围内,导流翼偏角为35°的网板（D1）具有较佳的水动力学性能;2）对双缝翼立式曲面V型网板,冲角为25°~35°时,前导流翼偏角为20°、中导流翼偏角为25°的网板（S3）具有较佳的水动力学性能。根据试验结果,建议D1网板最佳工作冲角范围为15°~30°,此时CL〉1.2且K〉2.0;S3网板最佳工作冲角范围为20°~30°,此时CL〉0.8且K〉3.0。导流翼偏角增加时网板升力系数的临界冲角有增加的趋势,合理调节导流翼偏角可以达到优化网板水动力学性能的目的。

矩形V型曲面网板和V型网板生产性对比试验

通过3个航次矩形V型曲面网板与V型网板作业性能和生产效果的对比试验。结果表明:在相同作业条件下,矩形V型曲面网板的水平扩张力可增大43.75%,阻力下降1.3%;试验船总产量和总产值分别比对比船提高18.13%和17.4%,试验船每消耗1 t柴油所获得的产量、产值与利润均可高于对比船。