The Influence of Flow on Creek Chub (Semotilus atromaculatus) Movement in an Intermittent Urban Headwater Stream

Fish movement in freshwater streams is often tied to patterns of flow, especially when the stream is intermittent, flashy, or some combination thereof. This relationship between flow and fish movement is exacerbated in small urban streams in impervious surface-dominated watersheds that lead to extreme flow conditions. This study focused on the response of Creek Chub (Semotilus atromaculatus), a common pioneer fish species in eastern North America, to flow events of various sizes in a small intermittent urban headwater stream. Our primary goals were to determine 1) the level of Creek Chub movement occurring in an intermittent headwater stream, 2) the influence of flow on movement direction and magnitude, 3) the degree of variation in individual movement behavior, and 4) mortality rates in the system. The study used PIT tagging and telemetry surveys to monitor Creek Chub movement over a six-month period. We found that individual Creek Chub in our study system were generally mobile (71%), but usually moved short distances only; however, a few individuals moved much farther, with a maximum single movement of 521 m. Moderate or major flow events increased the probability and magnitude of Creek Chub movement, and neither upstream nor downstream movement was favored. Movement was variable among individual fish and fish were able to respond to large and small flow events to move among habitats. Finally, we observed relatively high, but episodic, mortality in our study site, potentially related to pollution events. Evidence of elevated mortality emphasizes the importance of movement in highly disturbed streams, as it may enable recolonization after local extirpation.

淡水溪流中的鱼类移动行为通常与水流模式密切相关，当溪流为间歇性、骤发性或兼具两类特征时，这种关联尤为显著。在以不透水面覆盖为主的流域内的小型城市溪流中，水流与鱼类移动间的这种关联会被进一步强化——这类流域易引发极端水流状况。本研究以北美东部常见的先锋鱼类物种溪鲦（Creek Chub，Semotilus atromaculatus）为研究对象，探讨其在小型间歇性城市源头溪流中对不同规模水流事件的响应。本研究的核心目标包括：1）明确间歇性源头溪流中溪鲦的移动强度；2）解析水流对鱼类移动方向与移动幅度的影响；3）量化个体移动行为的变异程度；4）测算研究系统内的鱼类死亡率。本研究采用被动集成应答器标记（PIT tagging）与遥测调查技术，对溪鲦的移动行为开展了为期6个月的监测。研究结果显示，本研究系统内的溪鲦个体整体移动率达71%，但多数个体仅进行短距离移动；仅少数个体的移动距离较远，单次移动的最大距离可达521米。中等或大型水流事件会提升溪鲦移动的发生概率与移动幅度，且鱼类未表现出向上游或下游移动的倾向性。个体间的移动行为存在显著差异，溪鲦能够响应不同规模的水流事件，在不同生境间完成移动。最后，本研究在监测区域内观测到了偏高但偶发的鱼类死亡事件，其潜在诱因可能为污染事件。死亡率升高的现象进一步凸显了移动行为在高度受干扰溪流中的重要性——鱼类可通过移动在局部种群灭绝后完成重新定植。