The influence of flow on movement of a headwater specialist in an intermittent urban headwater stream

Abstract

Fish movement in freshwater streams is often tied to patterns of flow, especially when the stream is intermittent, flashy, or some combination thereof. Relationships between flow and fish movement are exacerbated in small urban streams in impervious surface-dominated watersheds that lead to extreme flow conditions. Here we examined 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 behaviour, 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, but there was no detectable asymmetry towards upstream or downstream directionality. 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 points to the potential importance of movement in highly disturbed streams, as it may enable recolonization after local extirpation.