WWRC 91-04
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 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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