Effects of electroshocking on macroinvertebrate drift in three cold water streams

The effect of electroshocking and walking on the substrate on macroinvertebrate drift was evaluated in three streams located in southwestern Oregon, USA. A randomized block experimental design was used to determine treatment (electroshocking and walking, electroshocking-only, walking-only) and drift distance effects on the number, biomass, and length of macro invertebrates drifting up to 30 in downstream. In all streams, electroshocking caused significantly (p < 0.05) greater number of macroinvertebrates to drift compared to merely walking on the substrate. The differences among treatments decreased the farther downstream the macroinvertebrates drifted. No significant difference) > 0.05) was observed in mean biomass between electroshocking and walking on the Substrate among the drift distances. The longest macro invertebrates were collected from the electroshocking treatment at the shortest drift distance (2.5 in) in all of the streams. The length of macroinvertebrates collected between electroshocking and walking on the substrate were similar at drift distances of 10 in and greater and represented predominately the smaller, poor swimming taxa.