Effect of removal of the fish population on the invertebrate fauna and phytoplankton of Emmaline Lake, Colorado

Abstract

Summer standing crop of phytoplankton, zooplankton, and macroscopic bottom organisms was sampled before (1964) and after (1965) removal of brook trout from Emmaline Lake, an alpine lake. Cirque Lake, adjacent to Emmaline Lake but barren of fish, served as a control. Brook trout were removed by rotenone (1 ppm) in September, 1964. Stomach samples of the trout, collected during the summer prior to removal, indicated that the trout consumed approximately 50 per cent aquatic and 50 per cent terrestrial organisms. Tendipedid larvae and pupae were the most abundant aquatic organisms in the stomachs. After fish removal, standing crop of phytoplankton did not change in either the control or experimental lake. Standing crop of zooplankton and macroscopic bottom fauna was significantly less in the experimental lake but was stable in the control lake. One season was not sufficient time for invertebrate populations to reach natural levels after the effect of rotenone. Prolonged effect of rotenone masked predator-prey relationships within Emmaline Lake.