Mitigation for the Construction and Operation of Libby Dam

The Libby FWP Mitigation Staff surgically implanted 28 coded acoustic and 12
combined radio/acoustic tags in burbot 6 trapping sites, respectively (Table 3). Each tag
had a unique frequency or code to allow for individual fish identification. The first
burbot was tagged on November 20, 2003 and the last burbot was tagged on April 26,
2004. The Libby FWP Mitigation staff has expended approximately 1-2 days per week
since trapping efforts began in November to search for tagged fish using primarily the
acoustic gear. Currently we have relocated the 40 burbot tagged with a coded acoustic
and combined radio/acoustic transmitters an average of 1.8 times per fish (Figure 17).
However, there were 3 combined radio/acoustic and and 7 acoustic tagged burbot, that
were not observed since release. We estimated that the mean home range was 6524 m
(range 166 – 27470 m; Table 3) for the 30 tagged burbot that relocated at least once. The
mean estimated depth of burbot that were relocated during daylight searches using
acoustic gear was 35.6 m, which was significantly deeper (p = 2.47*10 -67 ) than the mean
depth which we operated traps (14.8 m). We did not perform any nighttime acoustic
observations. We were not able to discern any clear movement patterns for the tagged
fish in terms of either upstream or downstream movement. Of the 40 tagged burbot, 14
of these fish had 3 or more relocation observations, six of these fish moving upstream, 7
moved downstream and one fish showed relatively little movement. However, we were
able to determine that many of the tagged burbot extensively utilized the old Kootenai
River channel and floodplain during daylight hours (Figure 18). For example, of the 14
tagged burbot for which we had at least 3 relocation observations, 11 of those fish were
consistently and repeatedly using either the old Kootenai River channel or floodplain
area. On average, the acoustic and acoustic/radio tags will be active until early 2006,
which will allow us to collect additional observations on the tagged fish, which in turn
will provide additional insight into the spawning distribution and habitat preferences of
burbot within Libby Reservoir.
68