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.

天然畅流河段可为诸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庇护栖息地。此类生物多样性庇护所同时也是保护学界关注的核心区域，因栖息于孤立生境片段中的物种，对局地环境变化往往尤为敏感脆弱。本研究依托长达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的鱼类物种衰退迹象——此前当地管理者与利益相关方已判定，当前及未来的土地利用可能对这两条河流造成潜在负面影响。科萨萨加河（跨佐治亚州与田纳西州）与埃托瓦河（位于佐治亚州），共同构成了被广泛筑坝的库萨河水系的畅流源头河段。这两条河流兼具重要保护价值，因其孕育了诸多受保护关注的物种，其中包含3种联邦级濒危鱼类与2种联邦级受威胁鱼类。本研究采用设于河流浅滩处的多个固定监测点的鱼类年度调查数据集，分析物种占用动态（occupancy dynamics）与物种丰富度（species richness）的时间变化趋势。分析过程纳入部分年份的重复定点调查数据，以估算并校正物种检测不完全带来的偏差；同时针对物种特异性（如稀有性、干流限制性）与年份特异性（如低/高流量日频次升高）的协变量对物种占用动态的影响开展检验。针对科萨萨加河13个监测点的26个物种的分析结果显示，几乎所有类群（taxa）的定居率均随时间下降，同时伴随物种丰富度的降低。4个类群（包含1种联邦级濒危鱼类）在科萨萨加河研究样地的占用率均有所下降，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。与之形成鲜明对比的是，埃托瓦河10个监测点的28个类群组成的相似水生动物群落，其物种存续率、定居率与占用率均未呈现显著趋势。两条河流的分析结果均显示，所有检验过的协变量对物种存续率与定居率均未产生显著影响。既往研究与观测结果表明，污染物输入、营养盐富集以及底栖生境变化，可能是科萨萨加河鱼类物种衰退的潜在诱因。本研究的分析结果可为评估科萨萨加河与埃托瓦河未来管理措施的实施效果提供基线数据，同时也展示了如何利用动态占用模型（dynamic occupancy models）从时间序列数据中验证动物群落衰退的相关证据。