Livestock grazing, golden trout, and streams in the Golden Trout Wilderness, California: Impacts and management implications
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Authors: R. A. Knapp, and K. R. Matthews
Date: 1996
Journal: North American Journal of Fisheries Management
Volume: 16
Number: 4
Pages: 805-820
Summary of Methods: Twelve habitat characteristics were measured inside and outside three livestock exclosures on two different streams in the Golden Trout Wilderness (118° 15' N, 36° 22' W), Sierra Nevada Mountains, California to determine the effect of livestock grazing on trout habitat. One exclosure was constructed in 1983, while the other two were built in 1991. Stream dimensions, water flow, substrate, and canopy height were measured among other variables along 125 m reaches at each site. Golden trout were surveyed using the electrofishing and willows were counted, and age-size classed along a two meter strip along the stream bank. Trout density was calculated as fish per square meter and fish per 125 meters stream reach. Measurements were taken in August of 1993 and 1994.
Article Summary / Main Points: Water depths and canopy shading were the variables with greatest differences between grazed and ungrazed sites and were less in grazed reaches than ungrazed. Willows were shorter and less plentiful in the grazed sites. Trout occurred in lower densities in the grazed reaches when measured as fish per area, but were typically denser when measured per stream length. Grazed riparian areas had less suitable trout habitat compared to ungrazed areas and had less fish per meter squared.
Vegetation Types: Riparian and Wetlands
MLRA Ecoregions: 18 Sierra Nevada Foothills 22A Sierra Nevada Mountains
Agrovoc Control Words: Riparian zones Rangelands Fish
Article Review Type: Refereed
Article Type: Documented Case History
Keywords: california golden trout, oncorhynchus mykiss aguabonita, habitat degradation, riparian vegetation, cattle grazing, threatened species, riparian health
Annotation: This study is fairly site specific due to the unique nature of exclosures; however, overgrazing can degrade many types of fish habitat and should be monitored accordingly. Because the exclosures were new, longer periods of recovery from overgrazing might have produced clearer patterns of trout density. The difference in fish density numbers between density per unit area and density per stream length is due the inclusion of stream width in the unit area measurements, which accounts for increased habitat. The results of the second part of this study can be found in Knapp et al. (1998, Ecol Appl:1104-1117) as part of the RSIS database.
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