Mitigation for the Construction and Operation of Libby Dam

Burbot Monitoring Below Libby Dam
The burbot catch in our hoop traps below Libby Dam has declined precipitously
since 1996/1997 (Figure 12). A total of 3 burbot were captured during the 03/04 trapping
season, which represented the lowest total catch and catch per effort (0.031 burbot per
trap day) on record since trapping began in the 94-95 trapping season. The most
numerous captures occurred in 1995-96 and 1996-97; these years correspond with higher
than normal snow-pack, and perhaps greater reservoir drafting. The mean annual catch
rate since the 1995/1996 trapping season was 0.668 burbot per trap day. However, the
catch rates since then have significantly decreased (r 2 = 0.742; p = 0.003; Figure 12).
This relationship was further improved using an exponential fit (r 2 = 0.930; p < 0.001;
Figure 12).
3
Fish/Trap Day
2.5
2
1.5
1
0.5
0
Linear All Years
r 2 = 0.376; p = 0.06
Exponetial; 96-04
y = 6.8193e-0.6864x
r 2 = 0.9303; p < 0.001
94-95 95-96 96-97 97-98 98-99 99-00 00-01 01-02 02-03 03-04
Trap Year
Linear 96-04
r 2 = 0.742; p = 0.003
Figure 12. Total catch per effort (burbot per trap day) of baited hoop traps in the stilling
basin downstream of Libby Dam 1994/1995 through 2003/2004. The data were fit with
linear regression for all years (1994/1995 – 2003/2004), 1995/1996 – 2003/2004 and with
an exponential model for 1995/1996 – 2003/2004. The traps are baited with kokanee
salmon and fished during December and February.
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