Kootenai River Fisheries Investigations; Stock Status of Burbot, 1999-2000 Annual Report

In Idaho, the burbot Lota lota are native only to the Kootenai River and are genetically distinct from burbot in the Montana reach of the river. Burbot once provided a substantial fishery with tens of thousands of burbot harvested annually. Burbot now number fewer than 1000 in the Kootenai River and Kootenay Lake and may be nearing demographic extinction. Studies completed in the winter of 1997-1998 indicated flow management at Libby Dam likely affected burbot spawning migration during winter. The objective of our study was to monitor the movement of burbot during a period of normal winter operation and a low flow period to test the null hypothesis (H{sub o}) that winter operation of Libby Dam does not affect burbot migration distance or travel rate. In addition, we monitored the stock status of burbot. We captured 36 burbot in Idaho and British Columbia with baited hoop nets. Twenty-three burbot were caught in Idaho, including 12 at Ambush Rock. The remaining 13 burbot were caught in British Columbia, including eight in the Kootenai River and five in the Goat River. One burbot escaped and was not measured, and one recaptured burbot was not measured. Burbot ranged from 332 mm to 705 mm total length (TL) (mean = 541 mm, SE = 14.02) and weighed from 350 g to 2,850 g (mean = 1,059 g, SE = 90.51). Relative weight (W{sub r}) ranged from 40.5 to 127.6 and averaged 88.6 (SE = 2.44). Population estimates for 1996, 1997, and 1998 were made for the Kootenai River from Bonners Ferry to Kootenay Lake; they were 738, 540, and 43 fish respectively. These estimates were not considered valid because we had so few recaptures, and confidence intervals could not be provided. Four burbot were implanted with sonic transmitters and their movement was monitored. We requested a low flow test (170 m{sup 3}/s) period of five weeks from the US Army Corps of Engineers (USACE) to study burbot migration distance or travel rate. The USACE could not provide an adequate low flow test period. Mitochondrial DNA (MtDNA) analysis indicated Duncan Lake, British Columbia burbot are genetically similar to Kootenai River fish and are a potential donor stock. The capture of eight post-spawn burbot and the subsequent examination of milt and gonadal tissue indicated they were in at least four different stages of reproductive readiness. These findings further support the hypothesis that high fluctuating flows from Libby Dam, which have continuously disrupted burbot migrations, may also be responsible for the failure of some burbot to spawn.