Behavior of a Stream-Dwelling Fish before, during, and after High-Discharge Events

Abstract

The movements of giant kokopu Galaxias argenteus were recorded before, during, and after high-discharge events in two small streams using radiotelemetry. Giant kokopu remained within defined stream reaches during base flow conditions. During high-discharge events, individuals either stayed within their home reach, moved and settled elsewhere, or moved and returned to their home reach as flows subsided. The variable behavior exhibited by individual giant kokopu suggested that reasons for moving during floods are complex. Reasons that may have influenced movement during floods included reproduction and mate searching, lack of adequate refugia, or some combination of these. In many instances, individual giant kokopu appeared to exhibit adaptive behaviors in response to high discharges. Behaviors supporting this view included fish not moving during the highest floods, fish moving upstream during the peak discharge period, and fish making purposeful “micromovements” (movements <5 m) into low-velocity habitats. This study shows that high-discharge events may play an important role in organizing populations of fish in small streams by providing opportunities for individuals restricted during base flow conditions to move to other stream locations.