1. Warming temperatures resulting from climate change may alter the distribution and abundance of many freshwater fish species, especially those in northern latitudes. Owing to interspecific differences in temperature adaptations and tolerances, warming may lead to changes in the fish community as a result of shifts in the abundance of co-existing species.
2. We investigated how increased temperatures have potentially affected the abundance and catch composition of anadromous salmonids in northern Europe. We used national angling catch statistics over a period of several decades (1993–2018) as a proxy of relative annual abundance of adult Atlantic salmon (Salmo salar), brown trout (Salmo trutta), and Arctic charr (Salvelinus alpinus) in water courses in Iceland and in northern Norway. These are the only locations in the world where the three species coexist naturally as anadromous forms, and where they are distributed across latitudinal gradients characterised by varying temperatures.
3. Interpolated data on average annual air temperatures proximate to the study rivers increased 1–1.7°C in northern Norway and 1.0–1.5°C in Iceland during the 26-year study period.
4. While the overall total number of fish caught has remained relatively stable during the period of study, gradual climate warming has been accompanied by a marked change in the catch composition of the three species in both countries. Increased temperatures were related to a decreased proportion of Arctic charr and an increased proportion of brown trout, while no temperature effect was found for Atlantic salmon. Controlling for the difference between fluvial and lacustrine systems, brown trout has begun to replace Arctic charr in all regions, whereas the relative catch of Atlantic salmon has been stable.
5. Interpretation of angling data can facilitate understanding of longer-term trends in catch data and provide insights into possible underlying changes in fish species and alert managers to shifts in abundance that might be mitigated by management actions. However, care must be taken to avoid the confounding effects that changes in fisheries management measures, angler preferences, and effort might have on the metrics of relative change used to make inferences about long-term trends.

中文翻译：

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北欧溯河鲑、褐鳟和大西洋鲑鱼相对丰度的时间变化：它们是否反映了气候变化？

1. 气候变化导致的气温升高可能会改变许多淡水鱼类的分布和数量，尤其是北纬地区的鱼类。由于温度适应和耐受性的种间差异，变暖可能导致鱼类群落的变化，因为共存物种的丰度发生了变化。
2. 我们调查了气温升高如何可能影响北欧溯河鲑鱼的丰度和捕捞组成。我们使用了几十年（1993-2018 年）的全国垂钓渔获量统计数据来代表水道中成年大西洋鲑 ( Salmo salar )、褐鳟 ( Salmo trutta ) 和北极鲑 ( Salvelinus alpinus )的相对年丰度在冰岛和挪威北部。这些是世界上唯一三个物种以溯河溯河形式自然共存的地方，它们分布在以不同温度为特征的纬度梯度上。
3. 在 26 年的研究期间，研究河流附近年平均气温的插值数据在挪威北部增加了 1-1.7°C，在冰岛增加了 1.0-1.5°C。
4. 虽然在研究期间捕获的鱼类总数保持相对稳定，但随着气候的逐渐变暖，两国三个物种的捕捞量构成发生了显着变化。温度升高与北极鲑鱼比例减少和褐鳟鱼比例增加有关，而大西洋鲑鱼没有发现温度影响。控制河流和湖泊系统之间的差异，褐鳟已开始在所有地区取代北极鲑，而大西洋鲑鱼的相对捕捞量一直稳定。
5. 对垂钓数据的解释可以促进对捕捞数据的长期趋势的理解，并提供对鱼类物种潜在变化的洞察力，并提醒管理者注意管理行动可能会减轻的丰度变化。然而，必须注意避免渔业管理措施、垂钓者偏好和努力的变化可能对用于推断长期趋势的相对变化指标产生混淆影响。