Density and biomass of redband trout relative to stream shading and temperature in southwestern Idaho
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Authors: B. W. Zoellick
Date: 2004
Journal: Western North American Naturalist
Volume: 64
Number: 1
Pages: 18-26
Summary of Methods: Response of redband trout (Oncorhynchus mykiss gairdneri) to stream shading and temperature of Big Jacks and Little Jacks Creeks under season-long grazing and no grazing, respectively in southwestern Idaho was investigated over two years. Topographic maps and aerial photographs were used to stratify each reach into 5 segments, based on stream gradient and canopy cover of riparian plant communities determined from. Trout density and biomass were estimated. Stream or bankfull channel, wetted channel, insolation, stream shading, shading from deciduous vegetation, shading from topographic features, and daily temperatures and fluctuations were measured in July.
Article Summary / Main Points: Along Little Jacks Creek, which received not grazing, stream shading was greater and solar insolation was lower than at Big Jacks Creek. In both streams maximum water temperatures increased with distance from headwater springs; temperatures increased more rapidly and to higher levels on Big Jacks Creek. Trout density and biomass were greater in Little Jack Creek when compared to Big Jacks Creek. Trout density was negatively correlated with increase in water temperature and solar insolation while biomass was negatively correlated with solar insolation and increased with stream shading. Warmer water temperatures in Big Jacks Creek were related to the reduced riparian shading. Water temperatures in Little Jacks Creek met Idaho water quality regulations, while the lower reaches of Big Jacks Creek did not meet these standards. Differences in temperature and trout abundance between the 2 streams indicate Idaho's cold-water criteria are appropriate for protecting redband trout populations.
Vegetation Types: Riparian and Wetlands
MLRA Ecoregions: 11 Snake River Plains 25 Owyhee High Plateau
Agrovoc Control Words: Riparian zones Streams Aquatic vertebrates
Article Review Type: Refereed
Article Type: Experimental Research
Keywords: redband trout, oncorhynchus mykiss gairdneri, water temperature, density, biomass, stream shading, solar insolation, desert streams, southwest idaho
Annotation: This replicated two year study and its results are applicable to most riparian areas and desert streams. As is true for all grazing research, the results are most directly applicable to areas with similar landscapes, species, level and season of use, and weather conditions. Season long grazing was the only grazing system that was examined and therefore limits use of these results in making of generalized statements. Examination of various levels of grazing intensities, seasons, and sites are needed. Different grazing systems, season of use, stocking rates and utilization levels may also achieve Idaho’s cold water criteria and the idea that livestock exclusion is the only way to achieve these standards may not be accurate.
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