Kootenai River velocities, depth, and white sturgeon spawning site selection – a mystery unraveled?
Article first published online: 2 DEC 2009
© 2009 The Authors. Journal compilation © 2009 Blackwell Verlag, Berlin
Journal of Applied Ichthyology
Volume 25, Issue 6, pages 640–646, December 2009
How to Cite
Paragamian, V. L., McDonald, R., Nelson, G. J. and Barton, G. (2009), Kootenai River velocities, depth, and white sturgeon spawning site selection – a mystery unraveled?. Journal of Applied Ichthyology, 25: 640–646. doi: 10.1111/j.1439-0426.2009.01364.x
- Issue published online: 2 DEC 2009
- Article first published online: 2 DEC 2009
- Received: December 31, 2008 Accepted: July 19, 2009
The Kootenai River white sturgeon Acipenser transmontanus population in Idaho, US and British Columbia (BC), Canada became recruitment limited shortly after Libby Dam became fully operational on the Kootenai River, Montana, USA in 1974. In the USA the species was listed under the Endangered Species Act in September of 1994. Kootenai River white sturgeon spawn within an 18-km reach in Idaho, river kilometer (rkm) 228.0–246.0. Each autumn and spring Kootenai River white sturgeon follow a ‘short two-step’ migration from the lower river and Kootenay Lake, BC, to staging reaches downstream of Bonners Ferry, Idaho. Initially, augmented spring flows for white sturgeon spawning were thought to be sufficient to recover the population. Spring discharge mitigation enhanced white sturgeon spawning but a series of research investigations determined that the white sturgeon were spawning over unsuitable incubation and rearing habitat (sand) and that survival of eggs and larvae was negligible. It was not known whether post-Libby Dam management had changed the habitat or if the white sturgeon were not returning to more suitable spawning substrates farther upstream. Fisheries and hydrology researchers made a team effort to determine if the spawning habitat had been changed by Libby Dam operations. Researchers modeled and compared velocities, sediment transport, and bathymetry with post-Libby Dam white sturgeon egg collection locations. Substrate coring studies confirmed cobbles and gravel substrates in most of the spawning locations but that they were buried under a meter or more of post-Libby Dam sediment. Analysis suggested that Kootenai River white sturgeon spawn in areas of highest available velocity and depths over a range of flows. Regardless of the discharge, the locations of accelerating velocities and maximum depth do not change and spawning locations remain consistent. Kootenai River white sturgeon are likely spawning in the same locations as pre-dam, but post-Libby Dam water management has reduced velocities and shear stress, thus sediment is now covering the cobbles and gravels. Although higher discharges will likely provide more suitable spawning and rearing conditions, this would be socially and politically unacceptable because it would bring the river elevation to or in excess of 537.66 m, which is flood stage. Thus, support should be given to habitat modifications incorporated into a management plan to restore suitable habitat and ensure better survival of eggs and larvae.