The influence of water velocity on the downstream movement of alevins and fry of brown trout, <i>Salmo trutta</i> L.

Abstract

Trout eggs were planted in four experimental stream channels, each channel being run at a different but constant discharge. Survival of the eggs to hatching was low and apparently unrelated to surface water velocity. However, movement of young trout out of channels was affected by water velocity, the higher the velocity the greater the proportion of trout that were lost. Virtually all fry moved out of a channel with a mean surface water velocity of 0.73 m s −1 . The rate of loss was not constant over the experiment but increased as the young trout entered the free‐feeding stage. At the end of the experiment loss of fry, after abrupt increases in discharge, was demonstrated in the lower velocity channels.