Compensatory density‐dependent (DD) processes play an integral role in fisheries management by underpinning fundamental population demographics. However, DD processes are often assessed only for specific life stages, likely resulting in misleading evaluations of population limitations. Here, we assessed the relative roles of intra‐ and inter‐life stage DD interactions in shaping the population dynamics of perennial freshwater fish with demographically open populations. Specifically, we monitored populations of amphidromous banded kōkopu (Galaxias fasciatus), giant kōkopu (Galaxias argenteus), and shortjaw kōkopu (Galaxias postvectis) in five streams where migratory post‐larvae are fished and in three no‐take (“closed”) streams located on New Zealand's South Island for two years. Using mark‐recapture data, we investigated whether fishing altered densities of “small” (non‐territorial recruits ≤1‐year‐old) and “large” (territorial fish >1‐year‐old) kōkopu size classes, and how subsequent density shifts affected the apparent survival and growth of each class while controlling for other confounding factors (e.g., habitat characteristics). We found that closed areas had substantially greater biomass of small kōkopu, particularly following the two‐month fishing season. Despite this greater influx of recruits, there was no difference in the biomass of large kōkopu at the species level, or as a combined assemblage between stream types. This indicated that although fishing of post‐larvae reduced recruit influxes into adult habitats, there was no subsequent evidence of recruitment‐limitation within adult populations. Instead, kōkopu demographics were underpinned by intra‐ and inter‐life stage DD competition and predation. Greater large fish densities played a key role in regulating the survival, growth, and/or presence of various kōkopu classes. In contrast, greater small fish densities had positive effects on the growth of opportunistic and insectivorous congeners, likely due to cannibalism and altered foraging behaviors, respectively. Our study details the prominent role of intra‐ and inter‐life stage DD interactions in regulating the population dynamics of perennial migratory freshwater fishes, even in populations with inhibited recruit and juvenile availability. We emphasize the importance for fisheries management to implement recruitment dependencies and complex interactions between distinct life stages to avoid deleterious DD responses and ensure population persistence.

中文翻译：

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评估多年生两栖鱼类管理的生命内和生命间阶段密度依赖性动力学


补偿性密度依赖性 （DD） 过程通过支撑基本人口统计数据，在渔业管理中发挥着不可或缺的作用。然而，DD 过程通常仅针对特定的生命阶段进行评估，这可能会导致对种群限制的误导性评估。在这里，我们评估了生命内和生命间阶段 DD 相互作用在塑造具有种群开放种群的多年生淡水鱼种群动态中的相对作用。具体来说，我们在捕捞洄游后幼虫的五条溪流和位于新西兰南岛的三条禁捕（“封闭”）溪流中监测了两栖带状 kōkopu （Galaxias fasciatus）、巨型 kōkopu （Galaxias argenteus） 和短颚 kōkopu （Galaxias postvectis） 的种群两年。使用标记重新捕获数据，我们研究了捕捞是否改变了“小型”（非领地新兵≤1 岁）和“大型”（领地鱼 >1 岁）kōkopu 大小类别的密度，以及随后的密度变化如何影响每个类别的表观生存和生长，同时控制其他混杂因素（例如，栖息地特征）。我们发现，封闭区域的小型 kōkopu 的生物量要大得多，尤其是在两个月的捕鱼季节之后。尽管新兵涌入量更大，但大型 kōkopu 的生物量在物种水平上或作为溪流类型之间的组合没有差异。这表明，尽管捕捞后幼虫减少了向成虫栖息地的新招募流入，但随后没有证据表明成年种群的招募受到限制。相反，kōkopu 人口统计数据以生命内和生命间阶段的 DD 竞争和捕食为基础。 更大的大型鱼类密度在调节各种 kōkopu 类的生存、生长和/或存在方面起着关键作用。相比之下，较大的小鱼密度对机会型和食虫同系物的生长有积极影响，这可能分别是由于同类相食和觅食行为的改变。我们的研究详细介绍了生命内和生命间阶段 DD 相互作用在调节多年生洄游淡水鱼种群动态中的突出作用，即使在新兵和幼鱼可用性受到抑制的种群中也是如此。我们强调渔业管理在不同生命阶段之间实施补充依赖性和复杂互动的重要性，以避免有害的 DD 反应并确保种群持久性。