Do Electrofishing Activities Disrupt Stream Biofilm Standing Stocks? An Assessment from Two Headwater Streams in Western Oregon

Humans affect ecosystems in many ways, and scienti?c ?eld studies are no exception. If data collection disrupts environments or biota too much, it can lead to inaccurate conclusions in the study of interest or in subsequent studies. We evaluated whether stream electro?shing surveys could measurably disturb the benthic bio?lms in two forested headwaters in western Oregon, USA. While the consequences of electro?shing to macroinvertebrates and ?sh have been assessed, to date no studies have quanti?ed its in?uence on benthic bio?lms. We observed declines in the standing stocks of accrued benthic chlorophyll a directly after electro?shing in both streams. After electro?shing, the standing bio?lm stocks declined by an average of ~15% in Oak Creek, a small third-order stream in the Oregon Coast Range Mountains, and by an average of ~34% in a third-order section of Lookout Creek, which is located in the western Cascade Mountains of Oregon, USA. In returning to Oak Creek 2 weeks after electro?shing, the standing stocks had fully recovered to their pre?shing levels. While the benthic bio?lm standing stocks did decline in association with electro?shing, the effects were small when compared with those of disturbances from common ?ow events and when scaling to the whole stream system. In Oak Creek, the proportional bio?lm standing stock decline from electro?shing activity was about 26% of what was observed following a moderate ?ow event (40% of bank-full discharge), and about 15% of the decline in bio?lm standing stocks following a complete bank-full discharge event (140% of bank-full discharge).