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This study evaluated habitat use of each species in relation to thermal conditions in the reservoir

complex, and described how annual reservoir elevation patterns influenced the spatial distribution of

fish. Specifically, the study a) documented seasonal habitat use by fish in four macrohabitat types of the

CML reservoir complex - Masonry Pool (MP), the main basin, delta, and the reservoir/river transition

zone; b) documented the seasonal and diel depth of bull trout and rainbow trout in the main basin of

CML, and c) described thermal conditions for bull trout and rainbow trout.

The adult fish tagging study was part of a larger effort to better understand distribution of adult bull trout,

rainbow trout and pygmy whitefish in the reservoir complex. Results corroborated bioenergetics

simulations, indicating that bull trout in CML occupy thermally suitable habitats during stratification such

that they do not experience prolonged stress or weight loss. Adult bull trout occurred throughout CML

but exhibited seasonal changes in depth and lateral distribution. Masonry Pool, on the west side of the

complex, was the least utilized habitat, and most tagged fish remained distributed at the eastern end of

CML where the Cedar and Rex rivers flow into CML. Bull trout use of the Cedar and Rex deltas was high

from winter through spring, and in summer bull trout moved to deeper and presumably cooler habitats

in the main CML basin. Concurrent detections of pygmy whitefish and bull trout in deltas during winter

and spring, along with increased proportion of pygmy whitefish in bull trout diets during these seasons,

suggested that delta habitats may be important foraging habitat for bull trout in spring.