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Summary The Kootenai River white sturgeon Acipenser transmontanus, an endangered species, spawns within an 18-km reach in the Kootenai River, Idaho, river kilometer (rkm) 228.0-246.0. Preliminary observations of adult white sturgeon have shown what appeared to be a progressive upstream movement during the spawning season, spawning over sand substrate seldom reaching the typical sturgeon spawning habitat of gravel and cobble located upstream of rkm 244.6. This behavior may be unusual for a white sturgeon population. The primary objecttive of this paper is to compare, within each spawning season and between seasons, the spatial and temporal pattern of egg collections (as an indicator of spawning location) and the spatial and temporal pattern of suspected spawners, as determined by their movement from 1994 to 1999. Adult white sturgeon were tagged with sonic and radio transmitters. Artificial substrate mats were deployed within three sampling reaches to determine approximate spawning locations and timing in reference to locations of spawners. Eggs were collected 207 different times from 1994 to 1999, including 123 times in the lower reach and 84 times in the middle reach. White sturgeon demonstrated a consistent temporal pattern of shifting spawning location as the season progressed, first spawning in the lower reach and then moving upstream to the middle reach. A total of 1234 contacts of potential spawners were made during May and June for the years 1994-1999. Some spawners were located in as many as four different locations from which eggs were collected within a season. There appeared to be at least five primary spawning locations, most in the vicinity of outside bends. This movement and temporal spawning pattern appears to be unique when compared with published studies on other sturgeon populations. Companion studies indicate that the species is not recruiting despite mitigative measures, and white sturgeon are thought to be spawning in unsuitable habitat. The combination of movement by white sturgeon within this sandy reach during the spawning season and spawning in unsuitable habitat may be contributing to the failure of recruitment. Present measures to recover the population may be inadequate. Further study is needed to determine if this movement pattern is caused by changing water velocities. Also, if historic spawning locations cannot be identified and rehabilitated, then we suggest consideration be given to habitat enhancement measures at the present spawning locations.

Each autumn and spring, adult white sturgeon Acipenser transmontanus migrate from the lower Kootenai River and Kootenay Lake, British Columbia, to prespawn staging reaches in Idaho. In spring, they migrate further upriver to a spawning reach near Bonners Ferry, Idaho. We monitored movement and behavior of 49 reproductively mature white sturgeon with radio and sonic telemetry from 1991 through 1997. White sturgeon responded to mitigated flows from 1994 through 1997, migrating substantial distances to a spawning reach soon after the onset of local runoff and rising water temperatures. Males migrated at temperatures of 5.5–12.1°C, 2 weeks before spawning; females followed about a week later, at slightly warmer temperatures. Females stayed in the spawning reach 1–28 d, averaging 10.5 d. Males spent 7 d to 2 months in the spawning reach, averaging 30 d. After spawning, 63% of the females moved immediately to Kootenay Lake; the remainder spent a longer time in the river downstream of the spawning reach...

The Kootenai River white sturgeon Acipenser transmontanus has been isolated from other white sturgeon populations for over 10,000 years, Bonnington Falls in British Columbia, Canada, creating the isolation. Libby Dam, constructed in 1972, modified the flow and temperature regime of the river, which affected spawning and recruitment of white sturgeon. Kootenai River white sturgeon are only known to spawn in a reach near Bonners Ferry, Idaho, 100 km downstream from the dam. In 2 of 8 years of study, only 15 white sturgeon eggs were collected over gravel–cobble substrate. However, in the other 6 years, 1,193 eggs were collected over sand substrate; these areas usually exceeded 5 m in depth, were within the main channel, and had water velocities of 0.2–1.0 m/s and temperatures of 8.5–12°C. In general, these characteristics differed from optimum white sturgeon spawning habitat in the Columbia River, where velocities average 0.8 m/s, water temperatures are 12–17°C, and gravel–cobble substrate is availa...

Sampling for adult Kootenai River white sturgeon Acipenser transmontanus began in March and continued through April 1999. Forty-six adult sturgeon were captured with 4,091 hours of angling and set-lining effort, while an additional three adult sturgeon were captured during gillnetting for juveniles. Flows for Kootenai River white sturgeon spawning were expected to be high because the snow pack in the basin was estimated at 130% of normal, but runoff came very slowly. Discharge from Libby Dam from mid-March through mid-June was maintained at 113 m{sup 3}/s (4,000 cfs). Flows in the Kootenai River at Bonners Ferry during early April, including local inflow, were 227-255 m{sup 3}/s (8,000-9,000 cfs) but increased gradually in late April to a peak of 657 m{sup 3}/s (23,200 cfs). Flows subsided in early May to about 340 m{sup 3}/s (12,000 cfs), but rose to 1,031 m{sup 3}/s (36,370 cfs) by Mary 26 because of local runoff, and white sturgeon began spawning. However, flows subsided again to 373 m{sup 3}/s (13,200 cfs) June 11, 1999 and some female white sturgeon with transmitters began leaving the spawning reach. Water temperature ranged from about 8 C to 10 C (45 F to 50 F) during these two weeks. On June 13 (two weeks after sturgeon began spawning), spawning and incubation flows from Libby Dam began. The flow was brought up to 1,136 m{sup 3}/s (40,100 cfs) and temperature rose to about 11 C (52 F). They sampled for 3,387 mat days (one mat day is a single 24 h set) with artificial substrate mats and captured 184 white sturgeon eggs. The Middle Shorty's Island reach (river kilometer [rkm] 229.6-231.5) produced the most eggs (144), with 388 mat days of effort; the Refuge section (rkm 234.8 to 237.5) with 616 mat days of effort produced 23 eggs; and the Lower Shorty's section produced 19 eggs with 548 days of mat effort. No eggs were collected above the Refuge section (> rkm 240.5) with 988 mat days of effort. They do not believe flows for sturgeon spawning in 1999 were very time for adequate spawning. Most spawning is thought to have occurred before the spawning flows, when 66% of the spawning events and 87% of the eggs were collected. Recommendations for the 2000 spawning season are given.

Flows in the Kootenai River for white sturgeon Acipenser transmontanus spawning in 1998 were expected to be at a minimum because the snow pack in the basin was only about 79% normal, and local inflow was expected to be very low, rkm 240.5). Four hundred and twenty (87%) of the 484 white sturgeon eggs collected in 1998 were viable. Development ranged from stage 12 to 28 (1 h to 12 d old), with 95% of the viable eggs at stage 21 (about 2.4 days) or earlier. The oldest egg was estimated at 293 hours old or about 12 days. Based on ages of viable eggs and the dates of egg collection, we estimated that white sturgeon spawned during at least 20 days in 1998. The first spawning episode was estimated to have occurred on May 6. The next episode was estimated to have occurred May 7 with a gap in spawning until May 10. Thereafter, spawning occurred for the next three days with a second break. From May 22, spawning occurred nearly every day through June 6. Peak spawning appeared to occur between from May 23 through May 28. Juvenile sampling yielded 163 individual fish (several fish were recaptured) of which 160 were hatchery and three wild sturgeon recruited from flow test years. Food habit studies of hatchery age-3 sturgeon indicated Chironomids comprised about 36% of the total food items by number while the Ephemeropterans Ephemerellidae and Baetidae contributed 22%. Continuous seismic profiling of a 12-km (7.45 mi) reach of the Kootenai River (rkm 228-240) indicated the riverbed was comprised primarily of fine and coarse sand. There was no evidence to suggest pre-dam gravels were overlain with sand. Recommendations for the 1999 spawning season include coordinating the flow test with sturgeon behavior and river temperatures of 8-10 C (46-50 F), and discharge should be in increments of 57 m{sup 3}/s (2,000 cfs) per day to a minimum of 1,130 m{sup 3}/s (40,000 cfs) at Bonners Ferry. We also recommend no load following.