Selection of Measures of Substrate Composition to Estimate Survival to Emergence of Salmonids and to Detect Changes in Stream Substrates

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 clarki pleuriticus in substrates ofdifferent 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 meas...

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