中国特有鱼类短吻间银鱼种群多样性变动及机理研究

Degradation of wild fish diversity is a worldwide problem threatening sustainable fisheries, but methods to evaluate the status and declining process of threatened fish species are unsound and need improving. Population diversity synthesizes divergent ecological and genetic attributes of populations and mends the evaluation system..Hemisalanx brachyrostralis is an ecologically important fish with one-year life span, which population sizes fluctuated frequently from year to year in relation to environmental changes. This species is spatially limited to the Yangtze River basin in small populations, and degraded severely in near decades, especially the last decade. So conservation study on this threatened species is important and necessary. .Focusing on one specific species, there existed a gap in biodiversity framework, and population diversity is a good supplement. Integrating variables from multiple disciplines of population ecology and population genetics, population diversity theory synthesizes as many characteristics as possible to give a full-scaled description on the status and changing process of a target species, making precise evaluation possible. Unfortunately, there is no strict population diversity study in China by far. So we will try the first study of population diversity on this declining fish species in this program..Spawns in dry months of early spring, population sizes of this species fluctuated frequently in relation to the water level (depth) at breeding grounds in spawning season. We collected specimen from 21 water bodies during 2001-2003, but some of them disappeared or declined to economic extinction level after the construction of the Three Gorges Dam in late 2003.Lacking of research, we know little about the status quo of this fish, and it’s necessary to conduct a specific study for better knowing its degrading mechanisms and effective conservation..In this program, we will first set up a population diversity model, integrating diffusive demographical characteristics and genetic diversity traits on Cytb and SSR analysis, to guide an exhaustive survey on all populations of this fish with the help of a new detection technique of Environmental DNA. Based on ecological and genetic data at local to regional scales, we will achieve an integrative evaluation of the species status. Compared with data collected in 2001-2003, we will further analyze the driving factors influencing the populations across these spatial scales. .This research addresses the following aspects over its entire geographically range. Ecological diversity variables will include basic population features, such as population size, sex ratio, body size distributions, reproductive ecology traits, population density and habitat occupancy. Genetic diversity variables include intra- and inter-population genetic differentiation and gene flow.

我国鱼类资源退化严重，而评价体系和退化机理研究缺乏。就受威胁物种的存在状态、退化规律和驱动力分析而言，现有的物种濒危等级和物种多样性、遗传多样性等指标均显单一而片面，种群多样性对物种特征的描述则系统而全面。短吻间银鱼是我国特有鱼种，现仅见于长江流域，处于快速退化之中。本题拟集成种群生态、空间生态和分子生态等学科技术，研究短吻间银鱼退化规律。采用环境DNA辅助调查全面获取短吻间银鱼基本种群生态学、空间生态学和环境变化特征数据；实验分析微卫星（SSR）和线粒体Cytb等基因标记，获取遗传多样性数据，建立模型综合评价其种群多样性状况。对比本组前期数据，分析其种群多样性近10年变化特点。整合单种群尺度到流域尺度上的种群多样性特征和三峡调蓄下的水文水位变化等环境要素数据，分析短吻间银鱼退化表现、推断关键驱动因子，揭示其退化机理，为该物种的科学管理提供科学依据，促进种群多样性理论和方法的发展和应用。

我国内陆淡水区域鱼类资源表现出大范围长时间持续退化，长江流域鱼类资源退化问题备受关注，但鱼类退化原因并不清楚。“长江无鱼”舆论促进了全流域全年禁渔的政策推进，但渔业资源和鱼类多样性状况不清、退化机理不明。在未弄清驱动因子及作用机理的条件所采取的强制性应急措施难见实效。.银鱼为一年生鱼类，是流域鱼类资源变动机制的良好的指示物种。4年来，课题组开展了流域尺度上短吻间银鱼的繁殖期、育肥期和越冬期的系统调查，揭示出短吻间银鱼资源遭受着极其强烈的生态压力，资源快速退化。自三峡库区至长江口仅见夏季育肥种群13个，越冬种群和繁殖种群5个，达到IUCN易危级别。遗传多样性研究结果显示，华阳河湖群各子湖种群实际为一个种群、鄱阳湖大湖和青岚湖为一个种群、梁子湖东西湖区为一个种群，洞庭湖白沙和西洞庭为一个种群、三峡库区为一个种群。种群间遗传距离和基因流结果表明鄱阳湖区短吻间银鱼与下游种群关系紧密，华阳河湖群和梁子湖群遗传结构特殊，三峡群与洞庭群关系紧密。三峡建坝前后遗传关系变动指示三峡群基因下泄对中下游种群的遗传影响与距离显著正相关。三峡建坝前后遗传多样性格局对比结果显示，三峡调蓄下，长江中下游短吻间银鱼种群间交流减弱，基因流明显降低，通江湖泊种群退化有违严重。稳定同位素分析结果显示银鱼与鲚属鱼类、餐和鲢、鳙等食谱接近，生态位重叠引起的竞争明显，但数量关系分析并未显示食物的致危压力。网捕调查、渔获物调查和环境DNA调查结果综合指示，水文变动导致的冬季越冬场水位过浅、春季产卵期无汛和冬春渔事扰动等是造成流域尺度上短吻间银鱼资源衰退的主要原因，三峡种群建立对下游种群的遗传扰动并非种群退化的诱因。水文调度是银鱼资源保护中应重点关注的内容。.