Influence of added habitat structures on the ecology of fishes in the Laramie River

Substantial effort and money are being directed toward river restoration projects that seek to restore aquatic organisms through habitat improvement. Common techniques include adding structural habitat to rivers to increase cover and habitat diversity, as well as installing rock riprap along banks to reduce erosion and sedimentation. More scientific evaluation of projects is needed for understanding effects on non-salmonid species, entire communities, and ecosystem functioning. In the Laramie River in southeastern Wyoming, two restoration projects were completed in 1987 and 2011, independently of one other. The fish assemblage in these reaches is dominated by warmwater nongame species. Two top predators are present in this system, native creek chub, Semotilus atromaculatus, and naturalized brown trout, Salmo trutta. The major goal of this study was to evaluate the influence of added habitat structures on the ecology of game and nongame fish by comparing results between two sites with added habitat structures (the Greenbelt and Monolith Ranch) to two sites lacking added habitat structures (Private Ranch and Paradise Farm). Paradise Farm was an outlier in terms of low habitat diversity and low fish density; however, species composition and diversity were similar between all sites. Most fish species were habitat generalists, and added habitat structures appeared to be beneficial to nongame fish species in the Laramie River as most species showed positive selection for both natural and added habitat types. Potential negative effects (e.g. predation) from brown trout appear to be buffered by other prey subsidies (crayfish and terrestrial inputs) and by other environmental factors limiting brown trout densities at these sites. Stomach content analysis showed the diets of top predators at the Greenbelt and Private Ranch were dominated by crayfish and contained small amounts of fish. Stable isotope analyses showed piscivory was low at both sites, as trophic position of top predators was similar between sites.