Temporal distribution of Kootenai River white sturgeon spawning events and the effect of flow and temperature

We examined the temporal distribution of endangered Kootenai River white sturgeon Acipenser transmontanus spawning, its relation to flow and temperature, and both natural and man-made variations thereof. We believed this information would be helpful because a Technical Management Team as well as the Kootenai River White Sturgeon Recovery Team manage flows, and, to a lesser degree, temperature thereof during each spawning season. Spawnings from 1994 to 2000 were monitored by egg collection using artificial substrate mats and subsequent microscopic examination of the eggs to estimate age and timing of spawning. The strength of our study was in correlation to observed spawning events with corresponding temperature and flow. We estimated that the number of white sturgeon spawning events ranged from nine to 20, with spawning days ranging from 17 to 31 days. Average daily temperature during spawning ranged from 7.5 to 14 degreesC, with the highest probability of spawning (48%) at 9.5-9.9 degreesC. Average daily flow for spawning events ranged from 141 to 1265 m(3) s(-1), but most ( 63%) spawning took place above 630 m(3) s(-1). Initial spawning by Kootenai River white sturgeon during spring may be synchronized with the arrival of females from downstream staging reaches. After the onset of spawning, the temporal distribution of spawning events appears to be dependent on the shape and stability of flow and temperature. We found a water temperature decrease of greater than or equal to0.8 degreesC could disrupt white sturgeon spawning. Our analysis suggests for optimum spawning in the Kootenai River that flows should be held above 630 m(3) s(-1), ideally 1200 m(3) s(-1), with a temperature range of 9.5-12 degreesC. Given the available flows, we found no evidence to suggest a need above 1300 m(3) s(-1) for white sturgeon spawning, but there may be secondary benefits associated with higher flows.