Effects Of Rotenone On Macrobenthic Invertebrates Of A Pennsylvania Stream

Although the use of rotenone as a fish toxicant is a common freshwater fisheries management technique, little is known of its effect on stream invertebrates. In this study pre- and post-treatment bottom samples of benthic invertebrates, collected from 4 study stations, were compared to determine the short-term effects of rotenone. Continuous drift sample~ collected throughout the treatment period provided additional qualitative information on the vulnerability of the benthic invertebrates to the toxin. Of the 4 major orders of macrobenthic invertebrates represented in Sinking Creek (Trichoptera, Ephemeroptera, Plecoptera, and Diptera), all exhibited substantial decreases in numerical abundance II days after rotenone treatment. Populations of Plecoptera (stoneflies) and Diptera (blackflies and midge larvae) were nearly exterminated, while densities ofthe 2 remaining taxa, Trichoptera (caddisflies) and Ephemeroptera (mayflies) were reduced to 50% of the pretreatment levels. A1l4 orders appeared in increased numbers in the drift samples taken during the treatment period.

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