1. Human-induced environmental change is a major stressor on freshwater habitats that has resulted in the population declines of many freshwater species. Ontogenetic shifts in habitat use and associated (st)age-specific requirements mean that impacts of environmental stressors can influence (st)ages in a population differently, and yet relatively few studies of freshwater fish populations account for their detail.
2. We aimed to identify environmental and biotic factors affecting survival estimated for six age-classes of a European grayling population in the River Wylye, UK over a 17-year period. We used a Bayesian age-structured state space model to estimate survival of grayling cohorts between subsequent life stages (eggs to age 5 adults) for 16 annual transitions (2003–2004 to 2018–2019), whilst accounting for imperfect sampling of the population. We quantified the effects of seasonal water flow and temperature, in-stream habitat and prey resource, and potential competitors and predators on survival between subsequent life stages. We used Bayesian variable selection to gauge their relative importance on survival.
3. Grayling abundances declined during the study period (>75% in all age-classes), predominately driven by a loss of mature adults. Changes to seasonal flows negatively influenced their survival: increased days of summer low flow related to decreased survival of subadults and mature adults, and lower winter flows related to reduced recruitment of juveniles from eggs. Higher summer macrophyte cover negatively influenced juvenile and subadult survival and increasing days of high temperature in summer appeared detrimental to juvenile survival. Abundance of brown trout (a potential competitor and predator) did not negatively influence grayling survival.
4. Our results reveal the implications of environmental change on a salmonid population, where recent low summer flows and high temperatures, and below average winter flows, have negatively influenced grayling survival. These conditions appear to be becoming more frequent and persistent in our study river, which is towards the species’ southern range limit, which could render the population vulnerable to climate change. Our study demonstrates how careful analysis of long-term population monitoring and environmental datasets can identify factors affecting (st)age-specific fish population dynamics, and when combined with local expertise, results in realistic mitigation proposals to promote wildlife population persistence.

中文翻译：

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中期环境变化影响鲑鱼种群的特定年龄生存估计

1. 人为引起的环境变化是淡水栖息地的主要压力源，导致许多淡水物种的种群数量下降。栖息地利用的个体发生变化和相关的 (st) 年龄特定要求意味着环境压力因素的影响可以不同地影响种群的 (st) 年龄，但相对较少的淡水鱼种群研究对其细节进行了解释。
2. 我们旨在确定影响英国威莱河 17 年间欧洲茴鱼种群 6 个年龄段的估计生存率的环境和生物因素。我们使用贝叶斯年龄结构状态空间模型来估计 16 个年度过渡（2003-2004 年至 2018-2019 年）的后续生命阶段（从卵到 5 岁成人）之间的鳟鱼群的存活率，同时考虑到不完善的人口抽样。我们量化了季节性水流和温度、河内栖息地和猎物资源以及潜在竞争者和捕食者对后续生命阶段之间生存的影响。我们使用贝叶斯变量选择来衡量它们对生存的相对重要性。
3. 在研究期间，鳟鱼的丰度下降（所有年龄段的>75%），主要是由于成年成年人的流失。季节性流量的变化对其存活产生负面影响：夏季低流量天数增加与亚成体和成熟成体的存活率降低有关，而冬季流量减少与从卵中招募的幼鱼减少有关。夏季大型植物覆盖度较高对幼鱼和亚成鱼的存活产生负面影响，夏季高温天数的增加似乎不利于幼鱼的存活。大量的褐鳟（潜在的竞争者和捕食者）不会对鳟鱼的生存产生负面影响。
4. 我们的研究结果揭示了环境变化对鲑鱼种群的影响，最近夏季低流量和高温以及低于平均冬季流量对鲑鱼的生存产生了负面影响。在我们研究的河流中，这些条件似乎变得更加频繁和持久，该河流接近该物种的南部范围限制，这可能使人口容易受到气候变化的影响。我们的研究表明，对长期种群监测和环境数据集的仔细分析可以确定影响（阶段）特定鱼类种群动态的因素，并与当地专业知识相结合，产生现实的缓解建议，以促进野生动物种群的持久性。