The Kootenai River white sturgeon population is physically isolated and genetically distinct from other white sturgeon populations in the Columbia River (Setter and Brannon 1990). Following the completion of Libby Dam in Montana, during 1972, the only year of significant recruitment in the population occurred in 1974, one year prior to full power plant operation in 1975. During subsequent years, a small number of naturally produced juvenile fish have been found but their abundance is too low to sustain the population. In 1994 the Kootenai River white sturgeon population was listed as endangered (USFWS 1994). Further protection was obtained in 2001 through the designation of 18 river kilometers (rkm) of Critical Habitat downstream from Bonners Ferry, Idaho (rkm 228- 246) (USFWS 2001). Monitoring locations of adult white sturgeon through telemetry studies and inferring general spawning locations from egg collections has consistently shown this reach to be the main region of spawning (Paragamian and others, 2001).
White sturgeon spawn by broadcasting their eggs which become adhesive shortly after exposure to water (Scott and Crossman 1973; Conte and others, 1988). Where successful spawning occurs in other river systems, eggs are assumed to attach to or settle into interstitial spaces provided by coarse substrates such as gravels and cobbles (Parsley and others, 1993; Parsley and others, 2002). Successful spawning of Kootenai River white sturgeon occurs annually within the critical habitat reach, confirmed by the annual presence of viable eggs and developing embryos (Paragamian and others, 2001). However, the river substrate under most flow conditions in the critical habitat reach is predominantly composed of fine sand with large migrating dunes (Barton 2004). Spawned eggs are presumed to settle onto the bed, and may become covered in the fine sand, or buried in the trough of migrating dunes resulting in suffocation and/or predation. Interestingly, within a few kilometers upstream from the spawning locations, the river is braided, relatively shallow, and has suitable substrate composed mostly of gravel and cobble.
Successful spawning and recruitment of Kootenai River white sturgeon involve complicated biological and ecological processes that may be affected by hydraulic and sediment-transport characteristics. Several hypotheses relating to the hydraulic and sediment transport characteristics of the Kootenai River have been put forth as possible explanations to the decline of successful recruitment in this system (Duke and others, 1999). First, in the post-dam period, the loss of naturally occurring high spring flow in addition to lower Kootenay Lake stages may have shifted the hydraulic spawning farther downstream into the current spawning reach. Prior to Libby Dam, higher lake levels or greater backwater extent and river stage may have encouraged the fish to spawn farther upstream in the braided reach. Second, the higher pre-dam discharge may have mobilized and scoured the bed sufficiently in the existing spawning reach to expose coarse-grained substrate suitable for egg hatching, and provided deeper water for upstream migrations areas that are very shallow in the post-dam era. However, it is likely that factors in addition to physical habitat alterations contribute to recruitment limitation and failure.
The goal of this study is to use the results of a preliminary set of 2D computational flow simulations within the 18-kilometer Critical Habitat reach to: (1) gain insight into the hydraulic conditions in the spawning reach, (2) assess whether these hydraulic conditions serve as spawning cues, (3) assess the effects of flow management (Kootenay Lake Stage and Libby Dam discharge) on those cues, and (4) gain insight into the role of pre- and post-dam flows in regulating the sediment substrate characteristics in the spawning reach.