An assessment of carcass counting surveys with increasing time lapse following a simulated fish kill on a small upland stream

A simulated fish kill was conducted on a small upland stream in Northern Ireland by planting out hatchery‐produced brown trout Salmo trutta L. carcasses of various size categories. Standard, post‐fish kill, assessment walkover surveys were conducted over time intervals to determine the number of carcasses visible. The sample variance between individual surveyors was generally low, with good agreement between the observed counts for the three, discrete, size fractions of fish up to 72 hr after the simulated fish kill. Despite low discharge rates, shallow water and good accessibility to the experimental stream, only 52% of the small category fish (<8 cm L_F) were recorded 4 hr after the start of the simulated fish kill. Larger carcasses (>17 cm L_F) were more visible, and >90% were detected 48 hr after the start of the simulated fish kill. After 96 hr, all size fractions of carcasses had reduced significantly, and the variability between replicate surveys increased markedly.     

Impact of the COVID-19 pandemic on agricultural exports

The COVID-19 outbreak has shocked the world's economies in the year of 2020. As this pandemic spreads around the globe, many experts feared that the global food supplies might start running short, especially if supply chains were disrupted. COVID-19 also added to the uncertainty of the business operation. Therefore, it is critical to understand how COVID-19 pandemic affected global food supply and market. In this study, we investigate the impact of COVID-19 on agricultural export companies in China using a unique firm-level survey data. We found that although on average agricultural businesses experienced declines in the exports, exports of some agricultural products especially grain and oil held strong and even increased, implying the essential demand for staple food during the pandemic. Not surprisingly, exports of medicinal herb also increased significantly during the pandemic. However, exports of goods such as edible fungus and horticultural products sharply decreased. Our results also showed that in general, impact of COVID-19 on smaller firms was more severe than that on larger firms. The results of this study can provide useful guidance and implications for agricultural businesses and policy makers on their COVID-19 mitigation efforts to navigate this global pandemic.     

基于无人机与激光测距技术的农田地形测绘

平整地技术是提高作物单产的重要措施，而获取高精度的农田地形测绘数据与农田数字地形模型，是进行精准平整地作业的必要条件。为了解决传统接触式地形测绘效率低、基于航拍摄影技术的遥感地形测绘精度差及作业成本高等问题，该研究提出了一种基于多旋翼无人机与激光测距技术的农田地形测绘方法。在多旋翼无人机测绘平台上搭载激光测距模块与后处理动态差分全球定位系统设备（Post-Processing Kinematic Global Positioning System，PPK-GPS），获取激光测距序列、PPK-GPS三维定位数据以及无人机的飞行姿态数据。首先使用均值滤波器处理原始激光测距序列，并将得到的激光测距序列与PPK-GPS定位数据进行同步处理，使二者建立空间对应关系。根据无人机倾斜状态时的测距激光方向与理论竖直方向的空间几何关系，使用从无人机的飞行控制器中提取的姿态信息校正激光测距序列，消除无人机平台在飞行过程中俯仰与横滚姿态变化对激光测距精度的影响。最后，根据PPK-GPS定位数据的海拔高度分量与激光测距序列计算试验地块内地面测量点的海拔高度，共获取1 417组地面测量点的有效测绘数据。利用手持PPK-GPS设备对地面测量点的海拔高度进行测绘精度检验。验证试验结果表明，本文提出的无人机农田地形测绘系统获取的海拔高度与手持PPK-GPS设备采集的海拔高度的均方根误差为5.2 cm，表明该无人机农田地形测绘系统具有较高的测绘精度。与利用手持GPS设备进行地形测绘作业的方法相比较，本文提出的无人机农田地形测绘系统具有自动化程度高、作业效率高等优点。该研究可为促进精准平整地技术的大规模应用提供数据支持。     

The effect of random and density‐dependent variation in sampling efficiency on variance of abundance estimates from fishery surveys

Abundance indices (AIs) provide information on population abundance and trends over time, while AI variance (AIV) provides information on reliability or quality of the AI. AIV is an important output from surveys and is commonly used in formal assessments of survey quality, in survey comparison studies, and in stock assessments. However, uncertainty in AIV estimates is poorly understood and studies on the precision and bias in survey AIV estimates are lacking. Typically, AIV estimates are “design based” and are derived from sampling theory under some aspect of randomized samples. Inference on population density in these cases can be confounded by unaccounted process errors such as those due to variable sampling efficiency (q). Here, we simulated fish distribution and surveys to assess the effect of q and variance in q on design‐based estimates of AIV. Simulation results show that the bias and precision of AIV depend on the mean q and variance in q. We conclude that to fully evaluate the reliability of AI, both observation error and variability in q must be accounted for when estimating AIV. A decrease in mean q and an increase in the variance in q results in increased bias and decreased precision in survey AIV estimates. These effects are likely small in surveys with mean q ≥ 1. However, for surveys where q ≤ 0.5, these effects can be large. Regardless of the survey type, AIV estimates can be improved with knowledge of q and variance in q.     

生猪保险查勘定损工作中的生物安全风险防范措施探讨

在非洲猪瘟防控新形势下,各猪场都高度重视生物安全,对生物安全风险防范工作提出了新的要求。在这种情况下,过去生猪保险查勘定损中的一些传统做法已经不能适应新形势,出现了猪场封闭式管理和查勘定损工作相冲突,病死猪理赔监督不到位、死亡原因不明、处理不及时以及部分查勘员生物安全意识淡薄等现象。对此,有关部门和机构应加强生物安全培训,采用网络和电子化等手段变革传统工作方式,在保险机构和畜牧兽医部门间加强联动和信息共享,把查勘定损、无害化处理和疫病监测溯源工作有机结合,把生物安全风险降到最低。     

清澜省级自然保护区红树林资源调查分析

通过样点实地调查,调查到海南清澜省级自然保护区具有真红树植物11科24种,半红树植物15科20种；根据组成种类,群落特征和立地条件,把红树林植物群落划分为12个红树林群系和4个半红树林群系。     

阳高县杏脯产业现状调查分析

山西省大同市阳高县被誉为"三晋杏乡",生产的阳高杏脯营养丰富,是山西省传统名优特产。调查了阳高县杏脯产业的发展历史和现状以及阳高县杏脯产业发展中存在的问题,并有针对性地提出了阳高县杏脯产业可持续发展的合理化建议。     

不同薏苡品种黑穗病发生情况调查

为筛选出适合宁化县推广种植的抗黑穗病品种，于2013年对当地种植的5个薏苡品种黑穗病发生情况进行调查，结果表明：龙薏一号黑穗病发病率最低，表现对黑穗病的抗性强，且产量较高，每667m2产量为257．43kg，适宜在薏苡黑穗病重发区推广种植。