Brachycentrus americanusandB. occidentalis(Trichoptera) in a Regulated Stream

Abstract

ABSTRACT Late instar Brachvcentrus americanus larvae were collected just prior to and during normally high spring runoff; adults were collected immediately following runoff; and early instar larvae appeared during the late summer low flow period of September and October. Brachvcentrus occidentalis adults were collected prior to normal spring runoff and early instar were first collected following runoff during moderate flows of July and August. Both strategies helped these species avoid stresses of high water velocities and sediment scouring often associated with spring runoff. During the study period, yearly high stream flows and maximum sediment movement occurred during summer flushing releases from Electric Lake, rather than the normal spring runoff period. Increased stream discharges with associated sediment movement that occurred when early instar Brachvcentrus larvae were present, appear to have had noticeable negative affects. Whatever the cause, following these occurrences, either species having ea...