The degree to which predation is an additive vs. compensatory source of mortality is fundamental to understanding the effects of predation on prey populations and evaluating the efficacy of predator management actions. In the Columbia River basin, USA, predation by Caspian Terns (Hydroprogne caspia) on U.S. Endangered Species Act (ESA)‐listed juvenile salmonids (smolts; Oncorhynchus spp.) has led to predator management actions to reduce predation; however, the assumption that reduced predation translates into greater salmonid survival, either within the life stage where predation occurs or across their lifetime, has remained untested. To address this critical uncertainty, we analyzed a long‐term (2008–2018) mark–recapture–recovery data set of ESA‐listed steelhead trout (O. mykiss) that were tagged (n = 78,409) and subsequently exposed to predation during smolt out‐migration through multiple river reaches (spatial scales), jointly estimating weekly probabilities of steelhead survival, mortality due to bird predation, and mortality due to other causes. This concurrent estimation across time‐stratified cohorts allowed for the direct measurement of the strength, magnitude, and direction of relationships between survival and Caspian Tern predation. Estimates of Tern predation on steelhead were substantial in most years, with cumulative annual estimates ranging from 0.075 (95% creditable interval = 0.058–0.099) to 0.375 (0.290–0.461). Increases in Tern predation probabilities were associated with statistically significant decreases in steelhead survival probabilities in all evaluated years and salmonid life stages (smolt out‐migration and smolt‐to‐adult returns). Results provide novel evidence that predation by Caspian Terns may have been a super‐additive source of mortality during the smolt life stage and a partially additive source of mortality to the adult life stage. Annual estimates of the difference between observed survival and baseline survival (i.e., in the absence of Tern predation) ranged from 0.052 (0.017–0.103) to 0.314 (0.172–0.459) during the steelhead smolt life stage and from 0.011 (0.001–0.029) to 0.049 (0.025–0.078) to the adult life stage. The estimated levels of compensation have important implications for predator management actions aimed at increasing the survival of endangered salmonids, and the modeling approach developed herein provides a framework to directly quantify the impacts of source‐specific mortality factors on prey populations.

中文翻译：

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在空间尺度上测量捕食对猎物生存的累加效应。

捕食对死亡率的影响是累加还是补偿性死亡的程度，对于理解捕食对猎物种群的影响以及评估捕食者管理行动的有效性至关重要。在美国哥伦比亚河流域，里海燕鸥（Hydroprogne caspia）捕食美国濒危物种法（ESA）所列的少年鲑鱼（大s；Oncorhynchus spp。），导致了捕食者管理行动，以减少捕食。然而，减少捕食转化为更大的鲑鱼生存率这一假设，无论是在捕食发生的生命周期内，还是在整个生命周期中，都未经检验。为了解决这一严重的不确定性，我们分析了ESA列出的硬头鳟鱼的长期（2008-2018）标记-捕获-恢复数据集（O。被标记的mykiss）（n = 78,409），随后在多个河流段（空间尺度）的臭鼬迁徙过程中遭受捕食，共同估算每周的黑头成活率，因鸟类捕食引起的死亡率以及由于其他原因造成的死亡率。跨时间分层队列的并发估计可以直接测量生存与里海燕鸥捕食之间的关系，强度，大小和方向。在大多数年份中，对海龟头部的Tern捕食的估计是相当可观的，累积年度估计范围从0.075（95％可信区间= 0.058-0.099）到0.375（0.290-0.461）。Tern捕食概率的增加与在所有评估年份和鲑鱼生命阶段（鲑鱼向外迁移和鲑鱼到成年返回）中的硬头鱼存活概率的统计学显着降低相关。结果提供了新的证据，表明里海燕鸥的捕食可能是在软体动物生活阶段的超级加性死亡率来源，并且是成年生活阶段的部分加性死亡率来源。在硬头mol生活期间，观察到的存活率和基线存活率（即在没有泰恩捕食的情况下）之间的年度估计差值介于0.052（0.017-0.103）至0.314（0.172-0.459）之间，以及0.011（0.001-0.029）之间至成人阶段的0.049（0.025–0.078）。