Displacement, velocity preference, and substrate use of three native California stream fishes in simulated pulsed flows

Abstract

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 river- rock substrate to determine the longitudinal displace- ment, 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 Sacra- mento 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 encoun- tered water velocity, and, presumably, conserving energy.