Diets of endangered silver chub (Macrhybopsis storeriana,Kirtland, 1844) in Lake Erie and implications for recovery

Silver chub (Macrhybopsis storeriana, Kirtland, 1844) is a native Cyprinid in Lake Erie, one of the Laurentian Great Lakes of North America. It is listed as endangered by the US state of New York and Canada, which has a recovery plan, and as special concern by the state of Michigan. Silver chub faces a potential threat to recovery from control efforts for invasive Grass carp (Ctenopharyngodon idella, Valenciennes 1844). Among the knowledge gaps for protection and restoration is current diet data. I describe the diet of silver chub from western Lake Erie in 2014, and I compare it to past studies to assess changes in diet through time. Silver chub captured in bottom trawls May–September 2014 were frozen in the field, and stomach contents were preserved in ethanol. Diet taxa were identified to the lowest practical taxonomic unit, then dried and weighed. Frequency of occurrence in silver chub diets was highest for Hexagenia spp. mayflies (79%). Dreissena spp. and Hexagenia spp. were both 41% of the diet by dry weight. Analysis of δ¹³C isotopes identified Hexagenia spp. as the primary source of carbon in silver chub. Compared to past studies, Dreissena spp. have mostly replaced Sphaeriidae and Gastropoda in silver chub diets. There also have been seasonal shifts in relative amounts of shelled organisms and Hexagenia spp. This study and past research suggest a functional link between silver chub and Hexagenia spp. abundance. Maintenance and recovery of silver chub may be dependent on maintaining Hexagenia spp. populations.     

Differing trophic niches of three French stygobionts and their implications for conservation of endemic stygofauna

1. Groundwater ecosystems represent the greatest proportion of unfrozen freshwater on Earth and harbour high numbers of rare taxa with restricted distributions. Stygofaunal abundance, species richness, and ecology play essential roles in groundwater ecosystem services and functioning, as well as providing an important contribution to global biodiversity. However, as global depletion and contamination of groundwater pose serious and often irreversible threats to stygofauna, more information is urgently needed about the ecology of rare groundwater species to guide effective strategies for their conservation or restoration.
2. In this study, analyses of carbon and nitrogen stable isotopes were used to compare and evaluate trophic niches and diets of a vulnerable stygobiont isopod, Gallasellus heilyi living in sympatry in French groundwater ecosystems with the isopod Caecosphaeroma burgundum and the amphipod Niphargus ladmiraulti.
3. Stable isotope results showed trophic niche partitioning among the three stygobiont species and indicated that G. heilyi and C. burgundum occupy the role of primary consumers and N. ladmiraulti that of predator. Moreover, although G. heilyi and C. burgundum were shown to rely on the same food sources, indicating similar diets, and their trophic niches did not overlap, suggesting trophic specialization.
4. The results suggest that detritus (i.e. decaying organic material) is an important food source for G. heilyi, and its availability could determine the survival of this endangered species. As a practical conservation measure for G. heilyi and the whole stygofauna community, we suggest reconnecting surface and subterranean ecosystems, as they probably were before natural sinks and many wells were filled up or closed.

     

Multi‐decadal climate and fishing predictors of abundance for U.S. South Atlantic coastal fishes and invertebrates

Abundance of marine stocks fluctuates in response to both internal processes (e.g., density dependence) and exogenous drivers, including the physical environment, fishing, and trophodynamic interactions. In the United States, research investigating ecosystem drivers has been focused in data‐rich systems, primarily in the North Atlantic and North Pacific. To develop a more holistic understanding of important ecosystem drivers in the Southeast U.S. continental shelf Large Marine Ecosystem, we applied generalized linear and dynamic linear modeling to investigate the effects of climate and fishing covariates on the relative abundance trends of 71 demersal fish and invertebrate species sampled by a coastal trawl survey during 1990–2013. For the assemblage as a whole, fishing effects predominated over climate effects. In particular, changes in trawling effort within the penaeid shrimp fishery governed abundance trends of bony fishes, invertebrates, and elasmobranchs, a likely result of temporal changes in bycatch mortality. Changes in trawling intensity induced changes in overall community composition and appear to have altered trophic interactions among particular species. Among climate indices investigated, the Pacific Decadal Oscillation and the Western Bermuda High Index were most prevalent in well‐supported dynamic linear models. Observed annual abundance trends were synchronous among some taxonomically related species, highlighting similar responses to exogenous influences based on life history. This study strengthens the foundation for generating hypotheses and advancing ecosystem‐based fisheries research within the region.     

四明湖水库浮游生物现状调查及评价

2006-2007年分4次对余姚四明湖水库水质理化指标、浮游生物群落结构进行了调查,并进行了多样性指数分析及渔产潜力估算。结果表明,四明湖水库浮游植物种类共计8门、47种（属）,其中以绿藻为最优势类群,占总密度的36.2%;浮游动物共计3大类、30种,其中原生动占40%;浮游植物年均生物量为10.20mg/L,浮游动物年均生物量2.36mg/L。从水体理化指标数据来看,四明湖水库水质属于II～IV类;从浮游植物群落结构和多样性指数分析结果来看,水库属于富营养水平;根据相关公式估算四明湖水库的鱼产潜力为20     

基于自适应趋近律的采摘机器人关节滑模控制研究

利用离散趋近律设计的滑模控制可有效抑制滑模控制中的抖动现象,但其抑制抖动的效果与离散趋近律的设计参数及系统的采样时间有着密切的关系。为此,在分析指数趋近律抖动的基础上,提出了一种自适应滑模控制器,Mat LAB能够进一步的提高基于趋近律的滑模控制器的抖动抑制能力。为了验证本文所提出方法的有效性,在Mat LAB中实现了该算法,并利用其来控制采摘机器人关节的伺服电机。仿真结果表明:本文所提的算法具有较好的位置跟踪能力,进一步地抑制了指数趋近律滑模控制中存在的抖动现象,提高了系统的性能。     

Comparative ecologies of domestic and naturalised rainbow trout in northern Lake Huron

Northern Lake Huron (Ontario, Canada) supports the largest concentration of freshwater salmonid cage culture farms in Canada and receives inputs of domestic‐strain rainbow trout (Oncorhynchus mykiss) through escapement. We assessed the potential effects of these domestic fish on the naturalised rainbow trout of this ecosystem by comparing their respective ecologies. Mature adults were sampled from spawning tributaries, primarily in spring, and to a lesser extent in fall. Fish of domestic origin comprised ~80% of rainbow trout sampled from sites near cage culture facilities but <20% of rainbow trout sampled from more distant sites. Domestic adults in spawning condition (gametes free‐flowing) were present in the spawning tributaries in both spring and fall sampling seasons, whereas naturalised fish in spawning condition were only observed in the spring. Domestic adults were younger and smaller (in length), appeared to have shorter lifespan and had a higher male to female ratio compared with their naturalised counterparts. Growth rates (change in length with age) of naturalised and domestic females in the wild were similar, but domestic males grew more slowly than naturalised males. Domestic females also produced smaller eggs than naturalised females. Food web positions (inferred from δ¹³C and δ¹⁵N) of domestic and naturalised fish were very similar but varied more strongly with body size in the former. Domestic‐strain rainbow trout of cage culture origin can survive, grow and attempt to spawn in northern Lake Huron and have the potential to compete for food, mates and spawning habitat with naturalised rainbow trout.     

东海和黄海南部七星底灯鱼摄食习性的研究

根据2008年5月至2009年2月东海和黄海南部4个航次大面调查所获得的七星底灯鱼(Benthosema pterotum)胃含物样本,对其食物组成、摄食强度、食物多样性程度及营养级进行了研究.结果表明,东海和黄海南部七星底灯鱼属浮游动物食性,桡足类是其最主要的食物类群,其％ IRI值、质量百分比和个数百分比分别为75...     

基于zigbee技术在矿井下节点切换机制的研究

节点接入切换机制和路由技术是井下定位系统的关键技术。根据矿井环境的特点，改进移动节点入网接入方式，提出移动节点地址分配的新方案。该方案中移动节点的地址不由协调器分配，在入井前由程序直接设定，且不随位置的移动而改变。仿真结果表明，提高移动节点入网成功率，减少了端到端的延时和丢包率，提高了数据传输效率。     

宽幅施药机械机器视觉辅助导航系统研究

为了实现宽幅施药机械喷幅的精确拼接,提出一种机器视觉辅助GPS导航方法。该方法首先对施药机械幅边喷洒泡沫剂并进行泡沫剂识别,识别过程中为了有效分割目标与背景,选定蓝色泡沫剂作为试验对象,提出使用超蓝色灰度化方案,并经过形态学滤波、行定位点的选取、Otsu分割提取泡沫剂信息,使用迭代的最小二乘法检测泡沫剂中心线的信息;然后给出了二维图形航向偏角和偏距的定义,并根据识别的泡沫剂信息进行航向偏角和偏差信息的提取,从而指导施药机械的行进方向。试验表明,所提方法可以较为准确地进行泡沫剂识别,根据泡沫剂信息识别得到的偏角计算值和实际测量值平均误差为1.58°,最大误差为2.5°,偏距计算值和实际测量值平均误差为5.4 cm,最大误差为8.4 cm,检测精度能够满足实际需求。     

车载式土壤光-电特性参数采集系统研究

土壤电导率是衡量土壤传导电流能力的一种固然属性,除了能够反映土壤质地外,还能够反映土壤的含水率、含盐量、有机物含量等特性。利用土壤光谱数据可以分析出土壤含水率、养分等,且测量过程中无需采样、搅动土壤。通过土壤电导率数据和光谱数据的综合、校正,能够提高系统的精度。基于嵌入式技术开发了土壤电导率和光谱反射率综合检测系统。土壤电导率测量系统采用基于改进的电流-电压四端法原理,使用深松犁的尖端作为电极传感器,能够在测量的同时完成松土的作用。光谱测量系统使用微型光谱传感器采集光谱数据,并进行实时处理。在采集土壤电导率、光谱数据的同时,系统同步采集GPS信息,并和土壤电导率、光谱数据一起保存,供进一步绘制土壤特性分布图使用。系统能够实时综合处理多种数据,并进行显示、保存等操作,具有良好的应用 前景。