A Method for Monitoring Movements of Small Fishes in Urban Streams

Abstract

The Front Range region of Colorado is an ecological transition zone between the Rocky Mountains and the western Great Plains. Changes to streams resulting from urban and agricultural land uses have contributed to the decline of many plains and transition zone fishes. The fragmentation of stream systems by dams, weirs, and diversions is among the most detrimental of these changes. These structures can inhibit fish spawning migrations, the search for sporadic resources, and recolonization of empty habitats. To assess the magnitude of the problem, there is a distinct need to determine whether existing instream structures are barriers to migration. A relatively simple method of doing so involves giving fish a unique mark and tracking their movements in the vicinity of a suspected barrier. We individually marked fish (15 species; 2,724 individuals) with visual implant elastomer (VIE) marks and tracked their movements across a grade control structure in Spring Creek in Fort Collins, Colorado. Results from a multistratum mark–recapture analysis showed that the grade control structure in Spring Creek prevented upstream movement by most fish. The approach we used identifies problematic instream structures that impede movements and present a potential stressor to fish assemblages in urban streams. The use of individual VIE marks is one of the few methods that can provide accurate information on the movements of small-bodied fishes in streams, but the commonly encountered design issues associated with this type of study must be considered.