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.

畅流河段为众多在原生分布区内其他区域已区域性灭绝的濒危水生生物提供了避难所。这些生物多样性避难所同时也是保护关注的焦点，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，以评估美国东南部两条河流中鱼类物种衰退的相关证据——当地管理者与利益相关方已确认当前及未来的土地利用可能对这两条河流产生不利影响。科诺索加河（横跨佐治亚州与田纳西州）与埃托瓦河（位于佐治亚州）是被大量水坝拦截的库萨河水系的畅流河源。这两条河流的重要性之一在于其孕育了多种受保护关注的鱼类，其中包括3种联邦濒危鱼类与2种联邦受威胁鱼类。本研究依托设于河流浅滩处的多个固定位点开展鱼类年度调查所获数据集，分析了物种占据动态与物种丰富度的时间变化趋势。部分年份中，我们对单个位点开展了重复调查，以此估算并校正物种检测不全带来的偏差；同时检验了物种特异性特征（稀有性、干流限制性）与年份特异性特征（低流量或高流量天数增多）对物种占据动态的影响。针对科诺索加河13个位点的26个物种的分析结果显示，几乎所有类群的定居率均呈现时间下降趋势，同时物种丰富度也随之降低。有4个类群（包含1种联邦濒危鱼类）在科诺索加河研究位点中的占据率有所下降，其中3个类群在研究的最后5年中似乎已完全消失。与之形成对比的是，埃托瓦河10个位点的28个相似鱼类类群的物种存续率、定居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居率产生显著影响。既往研究与观测结果表明，污染物输入、营养盐富集或底栖生境变化可能是科诺索加河鱼类物种衰退的潜在诱因。本研究的分析结果提供了基准信息，可用于评估未来针对科诺索加河与埃托瓦河的管理措施的有效性；同时也展示了如何利用动态占据模型，基于时间序列数据评估鱼类群落衰退的相关证据。