Aquatic systems are warming and exceeding upper thermal limits (UTLs) for many fish species, yet understanding how they inform resilience to climate change is challenging. Using Pacific salmon (Oncorhynchus spp.) as a model, we conducted a systematic review involving 168 papers investigating UTL in five species. We found considerable variation in UTL among species, within species and across life stages; largely attributed to methodological approaches (e.g. CT_max/UILT, Aerobic/Cardiac Scope, Thermal Migration Barriers, Rearing Mortality, Thermal Preference/Avoidance). Given that each method has strengths and weaknesses owing to logistics, time scale and ecological realism, we offer a new framework for assessing vulnerability to warming that stresses the importance of considering UTL metrics in the context of intended use (i.e. the development of management guidelines, projections of future persistence and survival) and what aspect (physiological or behavioural) of thermal response a metric investigates. Comparing studies with identical UTL approaches revealed that within species, UTL was higher for populations historically encountering higher temperatures—suggesting local thermal adaptation. Within populations, UTL differed across the lifecycle, being highest in fry and lowest in embryo and migrating adults, but this was not universal. For spawning Pacific salmon, UTL has not been assessed and few studies have examined estuarine and marine stages. Ultimately, this data gap limits the life-history thermal perspectives that can be drawn and may indicate a broader gap for all fishes, given that Pacific salmon are among the most well-studied species. Our framework illustrates the inherent and methodological inconsistencies in UTL and offers a guide for how thermal limits can best be used to assess the warming tolerance and vulnerability of fishes.

中文翻译：

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太平洋鲑鱼的耐热性：对物种、种群、生命阶段和方法的系统回顾

对于许多鱼类来说，水生系统正在变暖并超过温度上限 (UTL)，但了解它们如何增强对气候变化的抵御能力仍具有挑战性。我们以太平洋鲑鱼 ( Oncorhynchus spp.) 作为模型，对 168 篇研究 5 个物种 UTL 的论文进行了系统综述。我们发现物种间、物种内和不同生命阶段的 UTL 存在相当大的差异；很大程度上归因于方法论方法（例如CT _max /UILT、有氧/心脏范围、热迁移屏障、饲养死亡率、热偏好/避免）。鉴于每种方法因物流、时间尺度和生态现实性而各有优缺点，我们提供了一个评估变暖脆弱性的新框架，强调在预期用途的背景下考虑 UTL 指标的重要性（即制定管理指南、对未来持久性和生存的预测）以及指标研究热响应的哪些方面（生理或行为）。将研究与相同的 UTL 方法进行比较表明，在物种内部，历史上经历过较高温度的种群的 UTL 较高，这表明局部热适应。在种群内，UTL 在整个生命周期中有所不同，在鱼苗中最高，在胚胎和迁徙成鱼中最低，但这并不普遍。对于产卵的太平洋鲑鱼，UTL 尚未进行评估，也很少有研究检查河口和海洋阶段。最终，这种数据差距限制了可以绘制的生活史热视角，并且可能表明所有鱼类都存在更广泛的差距，因为太平洋鲑鱼是研究最深入的物种之一。我们的框架说明了 UTL 固有的和方法论上的不一致，并为如何最好地利用热限制来评估鱼类的变暖耐受性和脆弱性提供了指导。