Kootenai River White Sturgeon Spawning Migration Behavior and a Predictive Model

Abstract

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. Some (52%) males remained in the river, and the remainder migrated to Kootenay Lake. Female behavior and migration was more attuned to environmental conditions than was male behavior. Several environmental variables were examined to determine their effect on female white sturgeon migration to the spawning reach. Changes in temperature and river stage were the best predictors of the probability that females would migrate to the spawning reach. A logistic regression model, when applied to a subset of our original observations, correctly predicted movement to the spawning area 93% of the time. Our model can be used as a tool for risk assessment of white sturgeon spawning migration during various snow pack or temperature forecasts. It will be helpful in determining approximate migration or spawning times, making water management decisions, and assessing effects of temperature fluctuations. The model will be useful to continued study of white sturgeon by predicting spawning migration and improving efficiency in deploying sampling gear.