Razorback Sucker Movement Strategies across a River–Reservoir Habitat Complex

Abstract

AbstractRazorback Sucker Xyrauchen texanus occur in reservoir and riverine habitats in the Colorado River basin, with some individuals aggregating at river–reservoir inflows. To assess use of inflow areas and potential environmental correlates with fish movement among reservoir and river habitats, we used a passive receiver array to monitor location and movements (n = 69) and depth (n = 19) of acoustic‐ and PIT‐tagged fish in Lake Powell from April 2018 to March 2019. Acoustic receivers were deployed along 18 km of the San Juan River–Lake Powell inflow area, and a PIT tag antenna was deployed below a waterfall that impedes all upstream movement approximately 30 km upstream of the inflow area. Fish were detected moving between the inflow area and the river in all seasons except winter. Fifty‐eight percent of fish moved from the reservoir and were detected upstream at the waterfall, while 42% of fish appeared to remain within the reservoir. These reservoir‐resident fish moved long distances (hundreds of kilometers) but had relatively small linear home ranges (<18 km). On average, fish moved farthest and home range size was largest from April to September, and seasonal differences corresponded with differences in the number of fish detected. River discharge was relatively constant, and monthly distance moved was positively correlated with monthly river temperature, suggesting temperature alone might cue movements. Fish were detected at depths of 5.7 m but generally remained in shallow water (<2 m). Causal mechanisms that drive habitat use by adult fish are unclear but likely involve intraspecific differences in response to resource needs. We hypothesize that reservoirs provide warmer temperatures for longer periods of the year relative to regulated rivers, which might benefit warmwater fishes. Understanding the importance of movement among river and reservoir habitats might further conservation efforts by encouraging inclusion of reservoir habitats in management plans.