Kootenai River velocities, depth, and white sturgeon spawning site selection – a mystery unraveled?

Abstract

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 Ôshort two-stepÕ 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 postLibby 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.

Retrospective weight-of-evidence analysis identifies substrate change as the apparent cause of recruitment failure in the upper Columbia River white sturgeon (Acipenser transmontanus)

“…323 Due to lack of a positive recruitment effect a score of -2 was assigned for both contaminant 324 hypotheses. 586 The present findings add to a growing list of studies highlighting the importance of 587 substrate conditions in sturgeon spawning habitat (see Paragamian et al 2009;Kerr et al 588 2010; Du et al 2011). Most hypotheses received scores of -2 based on their 330 inability to explain the delayed recruitment failure of the Waneta group.…”

Kootenai River white sturgeon: synthesis of two decades of research

“…A more sophisticated approach was necessary (Paragamian et al 2009, McDonald et al 2010). Fisheries and hydrology researchers collaborated to determine whether the spawning habitat had been changed by Libby Dam operations.…”

“…Modeling suggested that higher discharges approximating 1600 m 3 s −1 or more for a period of 2 wk would likely provide more suitable spawning and rearing conditions (Paragamian et al 2009, McDonald et al 2010.…”

“…The present spawning location appeared to limit successful survival of embryos and larvae ). More suitable spawning substrates of cobble and gravel begin at Bonners Ferry and extend upstream from rkm 244.6, where a limited amount of spawning takes place (Paragamian et al 2009). Furthermore, it was not known where Kootenai River white sturgeon spawned pre-Libby Dam, and some KRWSRT members believed that they spawned in the more suitable reach of the river farther upstream, while others believed that the traditional spawning location could have been below Kootenai Falls ('the sturgeon hole') in Montana.…”

The effect of substrate rearing on the growth, development, and survival of larval white sturgeon (Acipenser transmontanus) during early ontogeny.

“…Currently, there is no clear understanding of the cause of recruitment failure; however, there is consensus that river regulation is a significant contributing factor (McAdam et al 2005;Paragamian et al 2001Paragamian et al ,2009). …”