Understanding the migratory community dynamics of river networks is important for maintaining lotic system integrity. River animals migrate to their preferred habitats in spatiotemporally heterogeneous river environments. Spring-fed habitats are uniquely characterized by stable temperature and flow regimes, which create suitable spawning habitats for the chum salmon Oncorhynchus keta. O. keta exhibits “run up” to its birthplace for spawning, especially during floods. Because the eggs deposited by this anadromous fish are nutritious and actively consumed by freshwater animals, the location and timing of O. keta spawning events affect the spatiotemporal accumulation of mobile consumers. In this study, we examined changes in temporal population density in spawning O. keta and a mobile consumer (juvenile O. masou masou) in a lowland, spring-fed tributary in northern Japan during a 48.5-mm autumn rainfall event. In both species, population density increased, and then decreased, after the rainfall event. In O. keta, these changes were closely associated with rainfall intensity, whereas in O. masou masou the peak was delayed until 3 days after the rainfall event. A comparison of the gut contents of O. masou masou sampled from a spring-fed tributary and an adjacent non-spring-fed tributary indicated greater consumption of O. keta eggs in the spring-fed tributary. These results suggested that preferential migration of O. keta into spring-fed tributaries for spawning induces subsequent accumulation of juvenile O. masou masou, in turn increasing O. keta egg consumption. These findings improve our understanding of community dynamics during floods in a heterogeneous river network environment.

了解河流网络的洄游群落动态对于维持灌溉系统的完整性非常重要。河流动物在时空异质的河流环境中迁移到它们喜欢的栖息地。春季喂养的栖息地的独特之处在于温度和流量稳定，这为大马哈鱼Oncorhynchus keta创造了合适的产卵栖息地。O. keta展品会“跑到”它的出生地产卵，尤其是在洪水期间。由于这种溯河鱼产下的卵营养丰富且被淡水动物积极食用，因此O. keta的位置和时间产卵事件影响移动消费者的时空积累。在这项研究中，我们检查了在48.5 毫米秋季降雨事件期间在日本北部低地、春季喂养的支流中产卵的O. keta和移动消费者（幼年O. masou masou）的时间种群密度变化。在降雨事件之后，这两个物种的种群密度先增加，然后再减少。在O. keta 中，这些变化与降雨强度密切相关，而在O. masou masou 中，峰值延迟到降雨事件发生后 3 天。O. masou masou肠道内容物的比较从一个泉源支流和相邻的非泉源支流取样表明，在泉源支流中消耗了更多的O. keta卵。这些结果表明，O. keta优先迁移到春季喂养的支流产卵会导致O. masou masou幼鱼的后续积累，进而增加O. keta 的鸡蛋消耗。这些发现提高了我们对异构河网环境中洪水期间社区动态的理解。