Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Natural Resources

Department name when degree awarded

Fisheries and Wildlife


Chris Luecke


A bioenergetics model was constructed for stream-resident drift-feeding salmonids. Model predictions of surplus power (energy available per unit time for lll growth and reproduction) were not statistically distinguishable from observations of surplus power in three laboratory studies. Of 40 experimental trials in these three studies, the model correctly predicted surplus power in 39 cases (p < 0.05).

I collected observations of rainbow trout (Oncorhynchus mykiss) focal velocity and physical habitat availability in the Green River of northeastern Utah, USA (1988-1990). In the winter of 1988, Flaming Gorge Dam generated hydropower and delivered an lJDStable discharge regime with a higher mean discharge to the Green River. During 1989 and 1990, Flaming Gorge Dam's operation was curtailed by drought. Therefore, the Green River exhibited a more stable discharge regime with lower mean daily discharge.

During winters exhibiting the stable discharge regime, all size classes of rainbow trout selected slower focal velocities than under an unstable winter discharge regime. Season had less influence on microhabitat selection of large fish than smaller individuals. Rainbow trout larger than 33 cm (total length) find and use positions with low focal velocities and high velocity shear regardless of season. In contrast, during the summer, fish less than 33 cm TL find and use positions with much higher focal velocities and greater velocity shear compared to the winter.

Four bioenergetic models were tested with the focal velocity use data. Two optimal goal models produced excellent fits (r2 = 0.91 and 0.93) to observed focal velocity use of rainbow trout larger than 33 cm TL. These results were consistent with the hypothesis that large rainbow trout were finding optimal focal velocity positions in stable discharge summers and under both discharge regimes in winter.

Rainbow trout movement was quantified along two scales with radio-telemetered fish: 1) weekly observations generated estimates of distances moved at intervals greater than one day and 2) multiple observations of a fish in one day produced estimates of distances moved over hours. I found an unstable discharge regime significantly reduces movement measured weekly (F = 11.10, P = 0.0019); hourly movement rates (m/h) were also reduced (F = 5.90, P = 0.0273).