Abstract Biologists have attempted to link intragravel survival of juvenile salmonids to changes in stream substrate quality caused by land management, but the failure to standardize measures of substrate composition has hindered this effort. We compared 15 such measures in laboratory tests that evaluated survival to emergence of Colorado River cutthroat trout Oncorhynchus claria pleuriticus in substrates of different composition. We also evaluated the sensitivity of three measures of substrate composition to the modification of stream substrates by spawning brook trout Salvelinus fontinalis and to the deposition of sediment in former redds of Colorado River cutthroat trout. Different estimates of the geometric mean particle size accounted for the greatest proportion of the variation in survival to emergence in laboratory tests, but the percentage of substrate less than 0.85 mm in diameter was the most sensitive measure of known changes in substrate composition in the field. We concluded that a single measure of substrate composition may be inadequate to both assess the potential survival to emergence in a substrate and detect changes in substrate composition caused by land use.
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