7610

• UCREFRP Catalog Number: 7610
• Author: Wick, E. J. and J. A. Hawkins.
• Title: Colorado Squawfish Winter Habitat Study, Yampa River, Colorado, 1986-1987
• USFW Year: 1987.
• USFW - Doc Type: Final Report Year 1.
• Copyright Material: NO

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"active" if its location changed within e 5 meter diameter circle over its
original location, as long as the specific habitat used remained the same.
"Local" movement was designated if a fish moved to new location outside the
original 5 meter diameter circle about its original location but within the
same specific habitat. The "moving" designation was used if a fish was
observed in the process of moving to a new location or had moved to a
different specific habitat type regardless of distance (ie: fish moved from
eddy to run or from one eddy to another eddy).
Habitat measurements
At the conclusion of a monitoring period habitat.measurments were taken at all
site locations at which fish spent 30 or more minutes. Site locations were 49
determined by triangulation from 2 to 5 transects which were previously marked
by survey flags placed along the bank during monitoring. Measurements taken
were water depth, velocity, substrate, cover, and water temperature. When fish
habitat was free of ice, measurements were taken from a boat or by wading.
When ice formed over the site location and was considered unsafe to walk upon,
access to the fish location was achieved by sitting in a small inflatable raft
at waters edge and pushing it over the surface of the ice using a wading rod.
Throughout most of the winter the ice was thick enough to walk upon safely.
However, as an added safety precaution a small inflatable raft was often taken
out on the ice and used to carry measurement equipment. Depth was measured
using a 10 foot wading rod (1\2 inch electrical conduit marked in 0.1 foot

increments). Velocity was measured using a Marsh- McBirney Model 201 current •
meter. Negative velocity was recorded if direction of current flow deviated
more than 90 degrees from that of the main channel current. Substrate was
categorized as a combination of primary and secondary components of clay,
silt, sand, gravel, coble or boulder by probing with a wading rod. Cover
designations included vegetation, brush, and boulder.

Three sets of measurements were taken at each site, one set was at the •
triangulated fish location (main site) with additional sets taken 1-2 meters
"in" toward shore and "out" away from shore. Velocity measurements at the main
site were taken at 0.2, 0.6, and 0.8 depth from the water surface when ice
free or from the bottom of the ice during ice cover. At the "in" and "out"
measurement sites velocity was measured at 0.6 depth. During ice cover,

habitat measurements were taken through holes drilled in the ice. Holes were •
drilled using either an 8 inch Strikemaster hand auger or 7 inch Strikemaster
gasoline power auger. Additional measurements were then taken to determine
ice-free water depth. These included solid ice thickness (ice below the water
surface in the hole), frazil ice thickness, and total depth (water depth in
the hole). Water depth below the surface of the ice was then calculated by

subtracting ice thickness from total water depth (Figure 2a). When frazil ice •
was present under the hard ice cover its thickness was determined by lowering
the velocity probe to the bottom, getting a positive velocity reading, and
then slowly raising the probe until the frazil could be felt touching the
probe and velocity decreased to 0.0 feet per second. The compact, non-moving,
frazil ice deposits were treated as solid ice in making water depth and

velocity measurements (Figure 2b). •
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