Data from: Long-term monitoring data provide evidence of declining species richness in a river valued for biodiversity conservation

Free-flowing river segments provide refuges for many imperiled aquatic biota that have been extirpated elsewhere in their native ranges. These biodiversity refuges are also foci of conservation concerns because species persisting within isolated habitat fragments may be particularly vulnerable to local environmental change. We have analyzed long-term (14- and 20-year) survey data to assess evidence of fish species declines in two southeastern U.S. rivers where managers and stakeholders have identified potentially detrimental impacts of current and future land uses. The Conasauga River (Georgia and Tennessee) and the Etowah River (Georgia) form free-flowing headwaters of the extensively dammed Coosa River system. These rivers are valued in part because they harbor multiple species of conservation concern, including three federally endangered and two federally threatened fishes. We have used data sets comprising annual surveys for fish species at multiple, fixed sites located at river shoals to analyze occupancy dynamics and temporal changes in species richness. Our analyses incorporate repeated site-specific surveys in some years to estimate and account for incomplete species detection, and test for species-specific (rarity, mainstem-restriction) and year-specific (elevated frequencies of low- or high-flow days) covariates on occupancy dynamics. In the Conasauga River, analysis of 26 species at 13 sites shows evidence of temporal declines in colonization rates for nearly all taxa, accompanied by declining species richness. Four taxa (including one federally endangered species) have reduced occupancy across the Conasauga study sites, with three of these taxa apparently absent for at least the last 5 years of the study. In contrast, a similar fauna of 28 taxa at 10 sites in the Etowah River shows no trends in species persistence, colonization or occupancy. None of the tested covariates show strong effects on persistence or colonization rates in either river. Previous studies and observations identify contaminants, nutrient loading, or changes in benthic habitat as possible causes for fish species declines in the Conasauga River. Our analysis provides baseline information that could be used to assess effectiveness of future management actions in the Conasauga or Etowah rivers, and illustrates the use of dynamic occupancy models to evaluate evidence of faunal decline from time-series data.

自由流动河段为诸多在原生分布区内其他区域已局部灭绝的受威胁水生生物区系提供了避难所。这类生物多样性避难所同时也是保护工作的重点关注对象，因为栖息于孤立生境片段中的物种往往对局地环境变化尤为脆弱。本研究分析了为期14年与20年的长期调查数据，旨在评估美国东南部两条河流中鱼类物种衰退的相关证据——这两条河流的当前与未来土地利用方式已被管理者及利益相关方认定存在潜在负面影响。科诺索加河（Conasauga River，跨佐治亚州与田纳西州）与埃托瓦河（Etowah River，位于佐治亚州）是筑坝密集的库萨河（Coosa River）水系的自由流动源头河段。这两条河流的重要价值之一在于其孕育了多种受保护关注的鱼类物种，其中包括3种联邦濒危鱼类与2种联邦受威胁鱼类。本研究采用了基于多个固定河床浅滩点位的年度鱼类物种调查数据集，以此分析物种占据动态（occupancy dynamics）与物种丰富度的时间变化特征。分析纳入了部分年份的点位专属重复调查数据，用以估算并校正物种检测不完备性（incomplete species detection），同时检验物种特异性（包括稀有性、干流限制性）与年份特异性（包括高低流量日频次升高）的协变量对物种占据动态的影响。针对科诺索加河的分析显示，在13个点位的26个物种类群中，几乎所有类群的定植速率均呈现时间下降趋势，同时伴随物种丰富度的降低。有4个物种类群（包含1种联邦濒危鱼类）在科诺索加河研究点位的占据率出现下降，其中3个类群在研究的最后至少5年中已完全未被监测到。与之形成对比的是，埃托瓦河10个点位的28个物种类群组成的鱼类区系，其物种存续率、定植速率与占据率均未呈现显著趋势。在两条河流中，所有被检验的协变量均未对物种存续率或定植速率表现出显著影响。既往研究与观测结果表明，污染物输入、营养盐负荷或底栖生境变化可能是科诺索加河鱼类物种衰退的诱因。本研究的分析结果提供了基准数据，可用于评估未来针对科诺索加河与埃托瓦河的管理措施成效，同时也展示了如何利用动态占据模型（dynamic occupancy models）从时间序列数据中评估动物区系衰退的相关证据。