Seasonal patterns of downstream movement in partially migratory stream‐dwelling Dolly Varden

Migration is a common behaviour among salmonids, but not all individuals within a population migrate, instead becoming residents and remaining in their natal streams. This phenomenon, known as “partial migration,” is well studied among sea‐run and lake‐run populations; however, the lower migratory benefits and costs for mainstem‐run individuals question whether the same mechanisms can be applied for stream‐dwelling salmonids. In this study, we investigated main stem‐run timing and body condition of partially migratory stream‐dwelling Dolly Varden charr (Salvelinus malma) in the Shiisorapuchi River in central Hokkaido, Japan. Based on commonly observed patterns in sea‐run and lake‐run salmonids, we predicted that migration would occur during spring and consist predominantly of age 1 +  females with some small subordinate males. Traps were placed at the mouths of two small tributaries along the Shiisorapuchi River periodically from May to December 2015. Adipose fin samples were taken for DNA to sex the individuals. Consistent to initial predictions, downstream movement occurs only once in the spring, dominated by age‐1 +  females. Trapped fishes (presumed migrants) were slightly longer but slimmer compared to the fish caught in the tributaries (presumed resident), which may be equivalent to smolts in anadromous populations. Regardless of migratory habitat, mechanisms driving partial migration in salmonids may be the same as long as production between natal stream and feeding habitats is significantly different.     

学习动机对大学英语教学策略的影响

从大学生学习动机的角度分析大学英语教师在教学过程中应注意的几点策略,力求将大学英语教学策略在理论和实践上得到进一步的提高。     

Using ecological indicators in the context of an ecosystem approach to fisheries for data-limited fisheries

The tenets of ecosystem approach to fisheries (EAF) now occupy centre stage in our efforts to maintain the sustainability of fisheries and rebuild marine ecosystems. The paper discusses how an EAF can be adopted for data limited fisheries and uses the northern South China Sea fishery as an example to demonstrate the selection and use of indicators for determining the states of the fishery and its relevant ecosystem to provide advice on management. Implementing EAF management requires indicators and models that address the impact of fishing across entire ecological communities and determine management actions to be taken to achieve the preset objectives according to decision rules. Data limited fisheries necessarily have limited resources for data collection and scientific studies and therefore could not support complex models. To overcome the data limitation and absence of modelling support, simple indicators have to be used to assess the current state and monitor changes of the fishery and its ecosystem. Such indicators should: (1) be observable and understandable by all stakeholders, (2) be based on easily obtainable and reliable data, (3) adequately reflect the condition of the resource, and (4) have associated reference values and responsive management measures. The paper also reviews the recent development and use of indicators and harvest strategies in both conventional and EAF management to better understand the differences and to shed light on the challenges of EAF, in particular for data limited fisheries.     

Stable isotopes and gut contents indicate differential resource use by coexisting asp (Leuciscus aspius) and pikeperch (Sander lucioperca)

Differential use of habitat and prey resources is an important mechanism that may allow coexistence of sympatric species. Unlike interactions between smaller cyprinid and percid fishes, the resource use by coexisting predatory asp (Leuciscus aspius) and pikeperch (Sander lucioperca) is relatively unknown. Here, gut content and stable isotope analyses were used to study ontogenetic dietary shifts and interspecific trophic niche overlap between asp and pikeperch coexisting in two reservoirs. The hypothesis that both species show an ontogenetic dietary shift from small invertebrates to large fish prey, but at the same time use different prey resources to reduce potential competitive interactions, was validated. The isotopic niches of the two predators showed no, or only a moderate, degree of overlap (0%–65%). The ontogenetic changes in the degree of interspecific isotopic niche overlap were different in the two reservoirs, suggesting that trophic segregation can be dynamic and variable among systems. Gut contents revealed that small (<100 mm standard length) asp consumed mostly terrestrial invertebrates and emerged aquatic insects, whereas small pikeperch foraged on zooplankton, larval and pupal stages of aquatic insects and fish. Larger individuals (>100 mm) of both species were predominantly piscivorous, with asp consuming more cyprinid prey and pikeperch more percid prey. Coexisting asp and pikeperch populations are able to utilise different prey resources, thereby reducing potential negative competitive interactions.     

大连海域刺参原产地大型底栖动物群落结构调查及修复策略

2014年6月,按照海洋资源调查规范,调查北黄海大连沿岸的刺参Apostichopus japonicas原产区中的旅顺口区塔河湾附近海域和大连金州新区城山头海滨地貌保护区海域内大型底栖动物的种类、密度、生物量,计算优势种、生物多样性和群落物种相似性,探讨其修复策略。结果表明,两处海域刺参生境大型底栖动物群落结构基本相同,优势种组成相似,优势类群均为软体动物;物种组成因饵料条件及周边海域底质不同呈现差异性分化;两处海域内海星类与刺参的密度比分别约为1∶3和1∶1,海星类与刺参的生物量比值与密度比相同;海星类与海胆类密度比均约为1∶1和3∶1,海星类与刺参及海胆类密度和的比分别为1∶4和1∶1,海胆类与刺参密度比均约为1∶2。根据调查结果认为刺参生境和增养殖区的养护、修复策略为:(1)多种共养,以参为主;(2)控制海星,适度增殖海胆;(3)提高初级生产力,降低污染。     

老年旅游市场开发研究

介绍了老年旅游的概念,分析了老年人的消费心理与老年旅游市场中存在的问题,并提出了开发老年旅游市场的策略。     

盐生植物种子异型性研究进展

种子异型性指植物在长期进化中,同一植株上产生多种在形态(颜色、质量)和结构(散布结构)及萌发、休眠特性等方面存在明显差异的种子.种子异型性现象在盐生植物中较为常见,多分为褐色和黑色种子,通常前者不休眠,萌发快,萌发率高,耐盐性强:后者休眠,萌发慢,萌发率低,耐盐性弱.盐生植物种子异型性是其对环境适应的重要特性,同时对种群的建立和繁衍有着重要的生态学意义.基于前人的研究对盐生植物异型性种子的形态结构及萌发、耐盐与休眠、产生机制及生态学意义等方面进行了综合论述,以期为相关研究提供参考.     

浙江省国家级重点保护植物的保护现状与保护对策

浙江省蕴藏着丰富的珍稀濒危植物资源,据调查研究,省内有国家级重点保护植物52种.其中,被列为1级重点保护植物的有13种,2级重点保护植物的有39种(包括变种).简要论述了浙江省珍稀濒危植物的保护现状,并提出了相应的保护对策.     

气候变化对中国农业生产的影响及应对策略

全球气候呈现变暖的趋势, 对农业生产和粮食安全产生重大影响, 并成为当今全球环境变化关注的热点问题之一。本文采用文献综述与比较研究的方法, 系统分析了气候变化对光资源、温度、土壤质量和水环境等农业生产要素的影响机理, 探讨了气候变化对我国作物种植区域和种植制度、农作物病虫害、农业生产能力以及农业经济与管理等方面的实际影响, 通过梳理国外应对气候变化的主要农业战略, 提出新时期我国应对气候变化的农业可持续发展策略。     

滇池粘皮鯔虾虎鱼食物组成及摄食策略分析

对粘皮鯔鰕虎鱼Mugilogobius myxodermus在滇池水体的食物组成、摄食策略进行分析,初步探讨其对滇池饵料资源环境的适应性,为进一步研究其生态入侵策略积累基础资料。在东大河湿地公园湖滨带设5个采集点,2014年5月9-10日及10月10日进行了2次样品采集,分别采集到粘皮鯔鰕虎鱼17尾、130尾。滇池粘皮鯔鰕虎鱼5月份种群内以成熟个体为主,10月份转变为以幼鱼为主。粘皮鯔鰕虎鱼消化道共检出23种食物类型,主要有多种枝角类、桡足类、介形虫及摇蚊幼虫等。以出现频率评价,5月份主要摄食枝角类、桡足类、摇蚊幼虫及蛹和介形虫,10月份主要摄食枝角类、桡足类、介形虫和摇蚊幼虫;以数量百分比评价,5月份较多的饵料种类为桡足类、尖额溞、摇蚊类幼虫和网纹溞,10月份较多的饵料种类为介形虫、桡足类和摇蚊幼虫、轮虫等。初步揭示粘皮鯔鰕虎鱼入侵早期种群具有喜好底栖食物的广食性特征,但仍需进一步探索其在滇池流域广阔生境中如何在不同时空尺度上针对不同的饵料基础所采取的摄食策略的差异,深入研究其在与先期入侵的近缘种的摄食竞争中如何取得生存机会。