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Response of trout populations in five Colorado streams two decades after habitat manipulation

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Evaluating the effectiveness of instream structures for increasing trout populations is complicated by a paucity of long-term studies. We report on a study spanning 23 years to assess the effect of installing log weirs on stream habitat and trout abundance. Structures were installed in a randomly selected half of a 500 m study reach in six small Colorado, USA, mountain streams in 1988, and habitat and trout abundance and biomass were measured annually from 1987 to 1994. When five of the streams were resampled in 2009, none of the 53 logs had moved, and all but one were functioning properly. Pool volume remained more than three times higher in treatment sections than in adjacent controls, and mean depth was also greater. Adult trout abundance increased rapidly after structures were installed and remained 53% higher in treatment sections than in controls 21 years later. Effects on juvenile trout abundance were not detected, probably because fry recruitment is strongly influenced by effects of snowmelt runoff, which vary annually among basins. This evaluation shows that instream structures placed in small, stable channels can function for more than two decades when properly installed and can cause long-lasting increases in trout abundance when habitat is limiting.

Document Type: Research Article


Affiliations: 1: Environmental Studies Program, Randolph–Macon College, Ashland, VA 23005, USA. 2: Department of Fish, Wildlife, and Conservation Biology, Colorado State University, Fort Collins, CO 80523, USA.

Publication date: December 6, 2011

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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