WWRC 91-21
Description of Brown Trout Redds in a Mountain Stream
Abstract
We sampled redds of brown trout Salmo trutta in a mountain stream to describe egg
location and substrate composition after spawning and during egg incubation. A single-probe
freeze-coring device was used to sample egg depth and substrate composition. We found eggs
throughout redds but most often in the front half of the tailspill (the substrate mound that accumulates
as the redd is excavated progressively upstream). Eggs were buried between 2 and 23 cm
below the substrate surface but were most frequently 9-12 cm deep. Spawning fish cleaned substrate
particles less than 6.3 mm in diameter from egg pockets, yet the percentage of particles smaller
than 1.7 mm in egg pockets was correlated with that outside redds. Egg pockets contained particles
larger than 50 mm more often than did any other location, indicating that particles of this size
were used as egg pocket centrums. The percentage of 1.7-mm and smaller particles in egg pockets
was higher in winter than in fall. We conclude that (1) spawning brown trout 20-40 cm in total
length substantially alter the substrate in egg pockets; (2) the amount of fine sediment in egg pockets
is positively correlated with that in the adjacent streambed; and (3) fines accumulate in egg pockets
during the incubation period.
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