The upstream passage of sturgeon (family Acipenseridae) past barriers such as dams has become a concern of fisheries managers in California. Knowledge about the swimming abilities of adult sturgeon species, particularly with relationship to fish ladders, is limited. Wild adult white sturgeon Acipenser transmontanus (n = 25; total length, 135–198 cm) captured in the San Francisco Estuary and Yolo Bypass toe drain were swum in a variable‐speed aluminum flume (24.4 m long × 2.1 m wide × 1.4 m deep) to evaluate swimming behavior around simulated fish‐ladder‐type partial baffles. Four baffle types (one horizontal ramp and three different vertical slot designs) set in two configurations were tested at three velocity regimes (velocity range around baffles, 0.28–2.52 m/s). In general, faster velocities (0.76–1.07 m/s) cued fish to swim upstream sooner (≤100 s). Among the baffle types, the percentage of successful passage was variable, and no statistically significant pattern was detected. The tail‐beat frequency of fish significantly increased in the high‐velocity (to 2.52 m/s) regions of the flume adjacent to the energy‐dissipating baffles, where sturgeon were able to pass by swimming in bursts, followed by a resting and recovery period in slower water. Successful white sturgeon passage structures should incorporate rapid‐velocity (e.g., 0.84–2.52‐m/s) sections between somewhat slower (e.g., 0.51–0.68‐m/s) sections for rest and recovery.

We studied whether fish were displaced longitudinally downstream by a 1-day whitewater kayaking pulse flow release from Camino Dam on Silver Creek, a tributary of the South Fork American River, California. On 15 September 2004 flows were increased from a base flow of 0.48 m 3 ·s -1 to a peak of 18.48 m 3 ·s -1 by midday, and decreased back to base levels. Rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) were observed in snorkel surveys before and after the pulse. Counts of youngof-the-year and juvenile trout were 26% and 9% lower after the pulse, respectively. Counts of adult trout were 12% higher. Six adult trout were radiotagged and were observed in the reach before, during, and after the pulsed flow. Our results suggest that most trout were able to remain in the study reach during the pulse, but that smaller fish may be more likely to be displaced downstream.

We studied whether juvenile fishes were able to maintain swimming speed and position during simulated river pulsed flows in a laboratory flume. We used a glass flume (15.24×0.6 m) with riverrock substrate to determine the longitudinal displacement, movement distances and frequencies, velocity selection, and substrate use of juvenile (SL range: 6.1± 0.2 cm) hardhead Mylopharodon conocephalus (n=13), rainbow trout Oncorhynchus mykiss (n=11), and Sacramento sucker Catostomus occidentalis (n=12) during a 100-min flow pulse, as velocity changed from slow to medium, fast, medium, and slow. Fish were capable of maintaining swimming speed and position up to the maximum flume velocity of 0.46 m·s −1 , except for one hardhead that impinged on the rear fish screen. Fish swam faster in the flume during the medium and fast intervals than the slow intervals, but fish speeds were similar among the medium and faster intervals, when some fish took cover behind the rock substrate. In comparison with a Brett-type swim-tunnel, fish showed less increase in mean swimming speed as the flume velocity increased. Fish in the flume were able to use the rock substrate as hydraulic cover, decreasing the encountered water velocity, and, presumably, conserving energy.

In regulated rivers, fluctuating water depths associated with pulsed discharges may strand small fish in side channels and pools. Quantitative assessments of stranded fish are difficult in field studies (e. g., due to unknown effects of avian and terrestrial vertebrate predators). To assess such lateral displacement and stranding on juvenile stream fishes, we designed, constructed, and tested (with three species) a 2×1-m, lateral-displacement flume. The flume featured a main channel that never drained and a raised, wide "floodplain" channel that alternately flooded, with a simulated pulse, and became dewatered. The floodplain contained four pools, with different shapes and draining capacities, in which fish could become stranded as the water level subsided. Fishstranding rates (8%) in this relatively compact laboratory flume, after exposure to simulated pulsed stream flows, were comparable to those observed in past investigations using larger, artificial streams.