Comparison of Methods to Verify Fish Passage through Remediated Culverts

Land- and wildlife-management agencies that work in aquatic systems have invested considerable resources to restore connectivity in fluvial systems affected by stream-road crossings.  Remediation activities such as culvert removal or installation of passage-friendly structures are expected to result in movement past the former barrier and utilization of the re-connected habitat.  Relative to the cost of remediation, much less money has been devoted to demonstrating biological effectiveness even though that is the ultimate goal.  Here we report on efforts to identify an efficient, cost-effective monitoring scheme to detect movement of trout past remediated culverts that biologists could use to demonstrate ‘success’.    We conducted a capture-mark-recapture study with native cutthroat and nonnative brook trout adjacent to remediated culverts in four streams in the northern Rocky Mountains of Idaho and Montana.  We marked or tagged trout above and below culverts, then monitored their subsequent movements by:  ‘traditional’ recapture using electrofishing, passive detection at fixed PIT-tag antennas located inside the culverts, and active detection with a mobile PIT-tag antenna.   Performance of each method was assessed by evaluating detection frequency relative to associated equipment and labor costs, and we also contrast these capture-mark-recapture results with those obtained  by genetic methods to detect fish passage.