Density‐dependent mortality of trout fry (Salmo trutta L.) and its relationship to the management of small streams

The natural mortality rate of trout fry and the impact of weed cutting and cleaning out of weeds, branches and twigs from the stream‐bed upon the mortality rate of trout fry was studied on several reaches in small streams. Above an initial density of 3.1 fry m–2 natural mortality rate was found to be density‐dependent in the first few months of life. In reaches where weed cutting and cleaning out of the stream‐bed had taken place the mortality rate was higher than that found under natural conditions in undisturbed reaches. The results support the suggestion that stream management works which make the stream more uniform will be in conflict with sound fishery management.