Winter Habitat Utilization by Stream Resident Brook Trout (Salvelinus fontinalis) and Brown Trout (Salmo trutta)

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Abstract
Habitat utilization by brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta) is described from three winters of underwater observations in a southern Ontario river. Older trout (>age 1) generally occupied positions in deeper and faster water than age 0+ trout. In winter, at sites of sympatry, brown trout occupied greater focal point water depths than brook trout; both species had similar focal point water velocities. At all sites, and for both age groups and species, there was a strong preference for positions beneath cover. Relative to summer, trout positions in winter were characterized by slower water velocities and greater overhead cover, In winter, most trout were in aggregations, usually in pools beneath cover and close to point sources of groundwater discharge. Gregarious behaviour appeared to increase as water temperatures decreased; no such relationship was evident in the summer. Specific strategies for overwintering varied between sites and age groups but generally conformed to the theory of energetic cost minimization for position choice. These variable patterns appear to be adaptive.