Mitigation for the Construction and Operation of Libby Dam

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Mountain Whitefish Mountain whitefish are one of three native species that have declined in abundance since impoundment of the Kootenai River (Huston et al. 1984, Figure 28). A natural logarithm transformation provided the best fit to the sinking gillnet catch data (Figure 33; r 2 = 0.598, p < 0.05). The trend in catch data for mountain whitefish during the first 13 years (1975-1988; mean catch = 3.5 fish per net) after reservoir impoundment decreased annually, until it reached a significantly (p = 0.0003) lower equilibrium with mountain whitefish catch rates since 1989 averaging 0.81 fish per net (r 2 = 0.14; p = 0.20). Catch rates since 1988 remained low; with mountain whitefish comprising an average of 1.1% of the spring catch during 1988 through 2003. We attribute the initial (1975-1988) mountain whitefish decline in Koocanusa Reservoir to the loss of spawning habitat and rearing habitat that resulted from a conversion of lotic to lentic habitat through reservoir construction. Rainbow and Westslope Cutthroat Trout Rainbow trout and westslope cutthroat trout catch have both significantly declined since the impoundment of Koocanusa Reservoir (Figure 33). Similarly to mountain whitefish gillnet catch data, rainbow and westslope cutthroat trout gillnet catch data was best with linear regression after performing a natural logarithm transformation (Figure 33). Although both species exhibit similar declining trends in catch since 1975, rainbow trout catch per net since 1975 has declined more precipitously than cutthroat trout catch per net. Rainbow trout have exhibited two general trends since impoundment. The first trend was the initial decline in abundance from 1975 to 1988, which is characterized by significant decline (Figure 33), followed by a period of relative stability from 1989 to 2003, where the average catch per net during this period (mean fish per net = 0.344) was not significantly different than a stable population (zero slope; Figure 33). Gill net catch of cutthroat trout in Koocanusa Reservoir exhibit a similar pattern, with the exception that that cutthroat trout catch rates exhibit 3 general trends through the same period. The first is a significant and precipitous decline during the early years of impoundment from 1975 to 1986 (Figure 33), where mean catch rates averaged 1.37 fish per net. The second general trend reduced abundance (0.38 fish per net), but at a level of stability from 1987 to 1993 (r 2 = 0.337; p = 0.172). The third general trend occurs from 1994 to 2003,and is characterized by a significantly lower level of abundance (0.136 fish per net; p = 0.001), and a somewhat stable level (r 2 = 0.023; p = 0.674). We believe that the period of general equilibrium during the period 1987-1993 may have been artificially elevated by the presence of hatchery cutthroat trout that were extensively stocked in the reservoir during this period (Table 7). Hatchery cutthroat trout were last stocked in the reservoir in 1994. 93
Catch per Net A. Mountain Whitefish 8 7 6 5 4 3 2 1 0 1975 1978 1981 1984 1986 1975-2003 Model Y = -1.9791Ln(x) + 6.5825 r2 = 0.5981 1988 1990 Year 1992 1994 1996 1989-2002 Model Y = -87.4 + 0.04*X r 2 = 0.14; p = 0.196 1998 2000 2002 Catch per Net B. Rainbow Trout 7 6 5 4 3 2 1 0 1975 1979 1981 1983 1975-2003 Model Y = -1.6172Ln(x) + 5.3343 1985 r 2 = 0.6387 1987 1989 1991 Year 1993 1989-2003 Model Y = -38.02 + 0.0192*X 1995 r 2 = 0.26; p = 0.054 1997 1999 2001 2003 C. Westslope Cutthroat Trout Catch per Net 3 2.5 2 1.5 1 0.5 0 1975-2003 Model Y = -0.7528Ln(x) + 2.4563 r 2 = 0.8636 1994-2003 Model Y = -5.92 +0.003*X r 2 = 0.023; p = 0.674 1975 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 Year Figure 33. Mean catch rates (fish per net) of three native species (mountain whitefish (a) in spring sinking gillnets in the Rexford area, rainbow (b) and westslope cutthroat trout (c) in floating gillnets from Tenmile and Rexford areas in Libby Reservoir, 1975 through 2003. The Tenmile area was not sampled during the fall from 2001-2003. 94
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Mitigation for the Construction and
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MITIGATION FOR THE CONSTRUCTION AND
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depth of burbot that were relocated
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ACKNOWLEDGEMENTS We are thankful to
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Juvenile Salmonid Population Estima
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deviation from reference conditions
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Figure 46. Minimal detectible diffe
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Chapter 2 Tables Table 1. Design sp
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INTRODUCTION Libby Reservoir was cr
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PROJECT HISTORY Montana Fish, Wildl
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2002 - Montana FWP collaborated wit
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DESCRIPTION OF STUDY AREA Subbasin
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Table 1. Current relative abundance
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Similar impacts have been observed
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2460 2440 2420 2400 2380 2360 2340
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construction and operation of Libby
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Chapter 1 Physical and Biological M
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Biological monitoring data was prov
Page 37 and 38: Figure 1. An aerial photograph of L
Page 39 and 40: antenna located approximately 5 cm
Page 41 and 42: We compared samples collected in Se
Page 43 and 44: extends downstream 131 m. This sect
Page 45 and 46: and reduced again to 28 ganged floa
Page 47 and 48: Results Bull Trout Redd Counts Grav
Page 49 and 50: Table 1. Bull trout redd survey sum
Page 51 and 52: Quartz Creek Bull trout redd counts
Page 53 and 54: Bull Trout Redds 40 35 30 25 20 15
Page 55 and 56: Keeler Creek Bull trout that spawn
Page 57 and 58: Burbot Monitoring Below Libby Dam T
Page 59 and 60: Table 2. Summary information for th
Page 61 and 62: 7000 6000 5000 Y = 45.246e 0.0055x
Page 63 and 64: The Libby FWP Mitigation Staff surg
Page 65 and 66: Table 2. (Continued) Capture locati
Page 67 and 68: Figure 18. Capture locations for a
Page 69 and 70: Table 4. T-test results. This table
Page 71 and 72: Figure 19. Montana Mountain Metrics
Page 73 and 74: Table 5. T-test results. This table
Page 75 and 76: Juvenile Salmonid Population Estima
Page 77 and 78: Grave Creek Juvenile salmonid monit
Page 79 and 80: Number Fish per 1000 Feet 100 80 60
Page 81 and 82: Libby Creek Section 1 of Libby Cree
Page 83 and 84: Figure 28. Rainbow trout, brook tro
Page 85 and 86: Pipe Creek Juvenile rainbow trout w
Page 87: Table 6. Average length and weight
Page 91 and 92: Table 8. Kamloops rainbow trout cap
Page 93 and 94: 25000.0 20000.0 15000.0 10000.0 500
Page 95 and 96: Burbot per Trap Day 3 2.5 2 1.5 1 0
Page 97 and 98: Table 9. Average catch per net for
Page 99 and 100: Table 11. Percent composition of ma
Page 101 and 102: deviation = 0.052; Figure 43), with
Page 103 and 104: Table 12. Individual probability va
Page 105 and 106: Discussion Long-term monitoring of
Page 107 and 108: We believe that Libby Reservoir dur
Page 109 and 110: Figure 47. Minimal detectible diffe
Page 111 and 112: References Bahls, L., R. Bukantis,
Page 113 and 114: trout status report (below Kootenai
Page 115 and 116: Chapter 2 Stream Restoration and Mi
Page 117 and 118: food sources, as evidenced by the l
Page 119 and 120: Methods and Results Eureka Pond The
Page 121 and 122: spacing was 172.8 feet, which repre
Page 123 and 124: Figure 2. Vicinity Map for Upper Li
Page 125 and 126: Table 1. Design specifications for
Page 127 and 128: 70 60 50 40 30 20 10 0 500 1000 150
Page 129 and 130: Grave Creek Phase I Restoration Pro
Page 131 and 132: Table 4. Design specifications for
Page 133 and 134: 190.0 185.0 180.0 175.0 170.0 165.0
Page 135 and 136: educed the mean width and width to
Page 137 and 138: Table 7. Mean cross sectional area,
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Discussion The Grave Creek Phase I
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References Chisholm, I.M., M.E. Hen
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Appendix 148
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Table A2. Lower Grave Creek Demonst
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Table A4. Libby Creek depletion pop
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Table A7. Mean zooplankton densitie
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Table A9. Mean zooplankton densitie
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Table A13. Yearly mean total zoopla
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Mitigation for the Construction and Operation of Libby Dam

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