| Abstract/Description or Keywords |
The status of burbot populations in reservoirs is of interest with respect to evaluating both footprint and operational impacts of BC Hydro dams. Arrow Lakes Reservoir (ALR) is located in the West Kootenay and is located downstream of two other large impoundments. Prior to this study, no directed assessment of burbot had been conducted on the reservoir. The primary objective of this study was to provide an initial assessment of the status of burbot in ALR including distribution, relative abundance, and size and age structure. Secondary objectives were to identify spawning locations and evaluate the use of an underwater video camera for line transect or mark-recapture population estimates. Distribution of burbot was determined using data from incidental catches during sturgeon set line sampling in 1995. Relative abundance was determined using catch-per-unit-effort (CPUE) in cod traps baited with dead kokanee. Traps were set in two widely separated locations (the narrows between the two main basins, and Galena Bay) from late October to early November of 2003, and one location (narrows) in late October 2004. Biological data were obtained from fish caught in the cod traps. All sampled fish were marked with Floy tags applied posterior to the dorsal fin prior to release. Ten fish were surgically implanted with radio tags during the trapping in 2003 and flights were conducted around the presumed time of spawning in an attempt to locate spawning areas. Underwater video camera surveys were conducted in the narrows area on 12-13 February 2004. Age was assessed using otoliths collected during a creel survey. Set line surveys indicated that burbot were widely distributed throughout the reservoir from Revelstoke Reach to Hugh Keenleyside Dam. Average number of burbot per overnight trap set was 4.5 and 4.7 for the narrows and Galena Bay respectively in 2003, and 8.5 for the narrows in 2004. Relative abundance, as inferred from trap CPUE, was the highest reported in the province. Median CPUE for baited traps in the ALR was more than 10 times higher than other B.C. lakes sampled to date with similar gear. Burbot in the ALR were relatively large in comparison with other B.C. lakes, with more than 90% of the trap catch exceeding 530 mm. Age structure showed some evidence of dominant and weak cohorts, but suggested relatively stable recruitment compared to Columbia Lake in the East Kootenay. There was large variation in length-at-age among individual fish; however, average growth rates in ALR were higher than most other B.C. populations for which data are available. Mature males ranged from 598 to 875 mm with two immature males at 510 mm. Mature females ranged from 630 to 860 mm and immature females from 510 to 640 mm. These mature fish would be age-5 or older. Flights located three of the radio-tagged fish after release. One was found near the mouth of Mosquito Creek and this is a likely spawning area for burbot. Another was located near the release site, and the third about 9 km north of the release site. Fish that were not detected may have spawned in deeper locations, or may not have spawned during the surveyed period. No aggregations of spawning burbot were observed in the narrows with the underwater video camera in February, however, the camera showed the types of habitat occupied and the daytime behaviour of burbot. Most burbot were resting inactive on the bottom and could be examined closely for the presence of a Floy tag. Therefore the camera might be useful for mark-recapture population estimates, if it was used immediately after a period of intense trapping and Floy tagging. burbot, Lota lota, fish, age, growth, maturity, cod, abundance, Floy tag, radiotelemetry, spawning, stock density, habitat, depth, substrate |
