Understanding how and why the size of populations varies is critical knowledge for conservation and management. While considerable work has explored how different demographic parameters affect population growth, less is known the drivers of variability in these parameters. Long-term time series tracking population size that are coupled with empirical data to examine the relative importance of different drivers are rare, especially in freshwater systems. Even rarer are studies that collect this information concurrently from multiple species with contrasting life history strategies in the same system to assess whether population size and the relative importance of drivers also vary. We studied changes in the abundance and size structure of four native freshwater fish species in the Murray River, southeastern Australia, over a continuous 19-yr period. Two species with traits typical of “equilibrium” species (Murray cod Maccullochella peelii and trout cod Maccullochella macquariensis) and two with traits of “periodic” species (golden perch Macquaria ambigua and silver perch Bidyanus bidyanus) were sampled annually and capture–mark–recapture modeling was used to ask (1) how did population size change during this period, (2) how were changes in population size related to variability in hydrology, and (3) how were changes in population size driven by different processes (local recruitment or migration events)? Populations of all four species varied throughout the study, and our results are consistent with the notion that local recruitment is an important driver of this variability for Murray cod and trout cod, whereas immigration is more important for the two other species. Increases in spring river discharge strongly influenced these responses for trout cod and golden perch. Our study provides fundamental insights into the population dynamics of these valued species, and how management strategies might differ based on their life histories. Management should focus on allowing connectivity for golden and silver perch, and on promoting local scale recruitment and survival for Murray cod and trout cod. More generally, our study highlights the importance of understanding the processes underpinning population persistence, how these processes may vary for different species, and ultimately how this knowledge can inform targeted management actions.

中文翻译：

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生活史是否介导排放作为淡水鱼种群数十年变化的驱动因素？

了解种群规模如何以及为何变化是保护和管理的关键知识。虽然大量的工作已经探索了不同的人口参数如何影响人口增长，但对这些参数变化的驱动因素知之甚少。跟踪人口规模的长期时间序列与经验数据相结合以检查不同驱动因素的相对重要性的情况很少见，尤其是在淡水系统中。更罕见的研究同时从多个物种收集这些信息，在同一系统中采用不同的生活史策略，以评估种群规模和驱动因素的相对重要性是否也有所不同。我们连续 19 年研究了澳大利亚东南部墨累河中四种本地淡水鱼类的丰度和大小结构的变化。Maccullochella peerii和鳟鱼鳕鱼Maccullochella macquariensis）和两个具有“周期性”物种特征的物种（金鲈Macquaria ambigua和银鲈Bidyanus bidyanus) 每年进行一次抽样，并使用捕获-标记-再捕获模型来询问 (1) 在此期间种群规模如何变化，(2) 种群规模的变化如何与水文变化相关，以及 (3) 人口规模的变化如何由不同过程（当地招聘或迁移事件）驱动的人口规模？在整个研究过程中，所有四个物种的种群都各不相同，我们的结果与以下观点一致，即本地招募是墨累鳕鱼和鳟鱼鳕鱼这种变异性的重要驱动因素，而移民对其他两个物种更为重要。春季河流流量的增加强烈影响了鳟鱼和金鲈的这些反应。我们的研究为这些有价值物种的种群动态提供了基本见解，以及管理策略如何根据他们的生活史而有所不同。管理应侧重于允许金鲈和银鲈的连接，并促进墨累鳕鱼和鳟鱼鳕鱼的本地规模招募和生存。更一般地说，我们的研究强调了理解支持种群持久性的过程的重要性，这些过程如何因不同物种而异，以及最终这些知识如何为有针对性的管理行动提供信息。