Population Dynamics and Extinction Risk of Burbot in the Kootenai River, Idaho, USA and British Columbia, Canada
Vaughn L. Paragamian, Brian J. Pyper, Michael J. Daigneault, Raymond C. P. Beamesderfer, and Susan C. Ireland
Abstract.—We examined the status and population characteristics of Kootenai River burbot Lota lota using capture–recapture data from 1993 to 2004. Our objective was to determine when this population may become functionally extinct and to help guide conservation efforts. A total of 403 burbot were captured, of which 300 were tagged and released, 31 were not tagged, and 72 were recaptures of fish tagged up to 4 years prior. Hoop-net catch per unit effort, where one unit of effort is a hoop-net set for 24 h, declined from 0.054 in 1996 to 0.008 in 2004. Mean total length of sampled burbot increased at a rate of about 8 mm/year from 1993 (516 mm) to 2004 (629 mm). Two models were developed for capture–recapture analysis, one that included effort data through a series of river reaches and one without effort data. The effort model appeared to be more reliable and suggested an average annual mortality rate for adult burbot (>250 mm) of 63%, an average annual recruitment of 77 fish, and an average estimate of 148 burbot in the Kootenai River from 1996 through 2004. Average declines in recruitment and population abundance were estimated to be 21% and 14% per year, respectively, resulting in estimates of only 20 recruits and a population size of only 50 burbot in 2004. These data confirm that Kootenai River burbot are in serious decline and may have already reached functional extinction. We conclude that immediate remedial measures must be implemented by focusing on rehabilitation of the native genetic stock and habitat remediation described in other studies.