Winter ecology of brown trout, white sucker and common carp in the Grand River, Ontario

The movement, habitat use, and swimming activity of adult river dwelling brown trout, white sucker and common carp were studied during winter. Movement was quite limited during the winter except during periods of high water discharge or the break-up of river ice. Both white sucker and common carp moved the longest distances during flooding and ice break-up. Brown trout movements were less affected. Both white sucker and common carp had positive relationships between mean weekly movements and water discharge. This relationship was also positive for brown trout, but not significant. During periods of high water discharge and ice break-up, white sucker and common carp used backwater habitats more and main channel habitats less. During high flows, brown trout tended to use runs more and pools less.; None of the three species of fish studied displayed a conspicuous daily rhythm of activity. About one third of the riverine brown trout studied were arrhythmic, and twilight was the only period which usually had the highest activity rates or was not significantly lower than any other period of the day. Diel swimming activity patterns of white sucker were generally arrhythmic or showed the least activity during night. Most common carp which were not arrhythmic were less active during the day than either twilight or night. After surface ice cover formed, the amount of activity at night, relative to day and twilight, decreased in brown trout. The swimming activity levels of most brown trout were changed by the presence of a solid surface ice cover. Water discharge appeared to have little influence on swimming activity of brown trout. Most white sucker and common carp showed a negative relationship between mean daily swimming activity and water discharge. Common carp were much more active than brown trout and white sucker.; Formation of a hanging dam filled over 80% of an overwintering pool with frazil ice and increased mean and bottom water velocities dramatically. Fish left the pool in which the dam developed but activity levels of fish leaving the pool were not affected in a consistent way.; Adult rainbow trout swam less when exposed to frazil and anchor ice in a refrigerated hydraulic flume. Fish appeared more sluggish during the ice events' and were not frightened when approached by observers (showed a reduce escape response).