Annual Progress Report 2000, Flathead River Native Species Project, Hungry Horse Mitigation

Muhlfeld, Clint; Glutting, Steve; Hunt, Rick; Daniels, Durae; Marotz, Brian

We collected microhabitat use data on juvenile and adult bull trout and westslope cutthroat trout using radio-telemetry (fall, winter, and spring) and snorkeling (summer) in two reaches (1 and 2) of the main stem Flathead River during 2000. Twenty-five westslope cutthroat trout and 60 bull trout were surgically implanted with radio-transmitters, released near their capture location, and radio-tracked throughout 2000 (Table 1). Each study fish was relocated at least once a week and movement and habitat use information was quantified at each fish location. In addition, snorkeling surveys were conducted during the daytime (1000-1600 hours) in Reach 2 from July through September 2000. Habitat use data will be used to construct habitat suitability index (HSI) curves for the IFIM model that will be used to estimate the weighted usable area for each microhabitat variable, by size-class and species, over a range of river discharges. Seasonal movement information will be used to identify critical spawning, rearing and overwintering habitat and describe seasonal movement patterns by various life history forms of native fishes in the upper Flathead River drainage. At each fish location (focal point), the following information was collected during radio-telemetry and snorkeling surveys (Figure 1): (1) total depth (m); (2) mean water column velocity (m/s); (3) bottom velocity (m/s); (4) substrate composition; (5) cover type(s) identified within a 1m2 radius of the focal point; (6) substrate embeddedness within a 0.5m2 radius of the focal point; (7) habitat type (i.e. pool, riffle, run); (8) channel location (mid-channel or near-shore); and (9) water temperature. In 2000, we collected habitat use observations on juvenile and adult bull trout (N = 389) and juvenile and adult westslope cutthroat trout (N = 212). In general, westslope cutthroat trout used low-velocity microhabitats (<2 ft./s) along channel margins in a variety of water depths (3-15 ft.) whereas bull trout utilized areas with higher velocities (< 3.5 ft./s) and moderate depths (4-10 ft.) (Figures 2-5). Adult bull trout generally used no cover or unembedded cobble and boulder substrate, whereas juveniles generally occupied deep habitats with unembedded substrate and large woody debris (LWD).

Annual Progress Report 2000, Flathead River Native Species Project, Hungry Horse Mitigation

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