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The population of white sturgeon in the Kootenai River has continued to decline since 1983, in spite of a closure to harvest in the U.S. section of the river. Setline and angling techniques were used to sample 228 sturgeon from the river between Kootenai Falls and Kootenay Lake during 1989. Sturgeon were found in Montana within 4 km of Kootenai Falls and downstream from Bonners Ferry, Idaho to Kootenay Lake, British Columbia. Our data indicate there is a complete lack of recruitment of juveniles into the population. The youngest fish sampled was of the 1977 year class, and the population is estimated at 850 individuals with 95% confidence intervals of 574 to 1,463. At present, we do not understand what mechanisms are limiting recruitment. Over the past 70 years, the lower Kootenai River has been extensively diked for flood control, effectively eliminating backwater and slough areas that may have provided juvenile rearing habitat: Contaminants have entered the river system via mining operations and agricultural practices. In 1972, Libby Dam began operation, reversing the natural flow regime of the river, and releasing frequent power peaking flows. Of 179 fish that were surgically sexed, 37% were female and 35% were male. Thirty-fourmore » percent of the females held developing oocytes. All oocyte samples from nine females contained copper (1.18 to 2.50 {micro}g/g) and zinc (15.6 to 32.8 {micro}g/g). Most samples also contained organochloride residues such as DDT, DDD, DDE, and PCBs (0.215 to 1.080 {micro}g/g, combined). River sediment samples contained 1.62 to 12.8 {micro}g/g copper and 22.4 to 70.6 {micro}g/g zinc, but no organochloride residues. Electrophoretic analysis of muscle samples indicated reduced heterogeneity compared with lower basin white sturgeon and showed a significantly different degree of variation between the two stocks in seven enzyme systems. An ongoing sonic telemetry study has revealed definite long distance movements in response to water flow fluctuations. Sturgeon regularly move across the British Columbia-Idaho border and seek out deep holes or migrate to Kootenay Lake during late fall. Adequate ranges in river depth and current velocity allow sturgeon to select for those habitat parameters; however, turbidity and temperature are homogeneous throughout the river at any given time.« less |
