Mobile brook trout in two high-elevation Colorado streams: Re-evaluating the concept of restricted movement

Movements of brook trout (Salvelinus fontinalis) were studied in two high-elevation (>2700 m) Colorado streams by marking (n = 4005) and recapturing fish using weirs and electrofishing at locations spaced up to 4500 m apart. Movement was most common in the upstream direction during summer, and about equal upstream and downstream between summers. Highest rates of movement occurred during and just after runoff, and before spawning, but substantial numbers of fish moved throughout the summer. Fish captured moving through weirs tended to be longer but in poorer condition than fish captured during electrofishing in 500-m reaches between weirs (i.e., the general population). On the basis of capture histories for individual fish, 59 and 66% in the two streams moved at least 50 m (up to 3380 m), even though most could be tracked only for several months. Thus, significant proportions of fish in electrofishing samples spaced throughout the stream bore marks from locations up to 2000 m away, indicating that long-range movements were relatively common. This conclusion is contrary to most literature on resident stream salmonids. We show how methods commonly used to study movement may be seriously biased, and suggest that movement may be more widespread than currently recognized.