The Effect of Rotenone on Zooplankton Populations in Freshwater Lakes

Abstract
Though the use of rotenone is a common procedure in freshwater fishery management, little is known of its effect on zooplankton. Fern Lake, a shallow dystrophic lake in western Washington, was treated with 0.5 p.p.m. of 5 percent rotenone powder in June 1960. Biweekly sampling of the open water, shore edge, and marsh area prior to and for 6 months following treatment provided quantitative and qualitative measurements of zooplankton populations. Open‐water species were completely removed, and remained absent for over 3 months. Organisms along the shore edge resisted the effect of rotenone, but eventually disappeared for several weeks. Those species inhabiting the dense weed patches did not all succumb to rotenone. The rare appearance of large numbers of males and usually early ephippial‐egg‐bearing female Cladocera were observed. Silver Lake, another shallow, dystrophic lake, was treated with 1 p.p.m. of rotenone in September 1960, and an immediate effect on the zooplankton populations was observed. The rotenone penetrated to the thermocline at the 30‐foot depth in the first 6 hours, killing Cladocera and Copepoda as it sank. A most significant observation for fishery management was the length of time that zooplankton, organisms important as fish food, were absent from the lake. Preapplication zooplankton populations were not established until several months after the lakes had become nontoxic to fish and had been restocked.

This publication has 0 references indexed in Scilit: