Ascent Behaviors of Nine-spined Sticklebacks in Orifices and on Overflow Weirs of Fishways

Abstract

  Experiments on the ascent behaviors of nine-spined sticklebacks (Pungitius sp. 1) were conducted in a submerged orifice weir and on an overflow weir in an experimental flume. The ascent behaviors of the fish were identified using a high-speed camera to measure the ground speeds and ascent routes of sticklebacks. The flow velocities in and around the orifice and on and around the overflow weir were measured using a three-dimensional velocity meter and particle tracking velocimetry. Stickleback swimming speed in the ascent route was calculated based on ground speeds and flow velocities. In the experiments with the orifice weir, most sticklebacks passed the middle area of the orifice, where flow velocity was relatively slow. Conversely, in the experiments with the overflow weir, most sticklebacks passed over the weir, where flow velocity was relatively fast. In the experiments with the orifice and with the overflow weir, the swimming speeds of sticklebacks were 8–39 and 9–21 times their body lengths, respectively. The results indicate that many sticklebacks ascend in areas where flow velocities were faster than their burst speed, which is defined as 10 times their body lengths.