Effect of velocity regime on ontogenetic dispersal and habitat use of Kootenai River White Sturgeon (Acipenser transmontanus , Richardson, 1836) early life stages: An artificial stream study

Abstract

Summary The effect was studied of two channel velocity regimes (slow regime = mean, 16.9 cm s−1; fast regime = mean, 23.4 cm s−1) on the behaviour and dispersal of Kootenai River white sturgeon Acipenser transmontanus early life stages (ELS = free embryos, larvae, early-juveniles) in artificial streams. A conceptual model incorporating velocity effects on ELS behaviour and dispersal follows that: (1) most free embryos hide under cover and do not disperse in any velocity; (2) the velocity regime has the greatest effect on peak dispersal by larvae − dispersal is intense and short (11 and 13 days in 16.9 and 23.4 cm s−1, respectively); and (3) the long peak and valley dispersal (alternating periods of intense and slow dispersal) by post-peak larvae and early-juveniles, which lasts to day 74 post-hatch (early-September) for some fish, is not affected by the velocity regime. Edge velocity habitat (about 4 cm s−1 between eddy and channel velocities) was used by 65% of the late-larvae foraging on drift during the day in either a slow or fast velocity regime, the edge being used even more at night (75% in fast velocity, 82% in slow velocity). Early-juveniles also used edge habitat. Regulation of river flow should maintain a minimum 23 cm s−1 bottom velocity regime in the larval dispersal reach to trigger an intense dispersal from the spawning reach and enable fish to disperse quickly downstream.