7762

• UCREFRP Catalog Number: 7762
• Author: Valdez, R. A. and B. R. Cowdell.
• Title: Annual Summary Report-1994, Effects of Flow Regulation and Ice Formation on Overwinter Nursery Habitat of Age-0 Colorado Squawfish in the Green River Below Flaming Gorge Dam.
• USFW Year: 1994.
• USFW - Doc Type: \
• Copyright Material: NO

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Backwaters which became inundated were not considered usable habitat. Reductions in backwater size were
not considered significant unless the total area became less than 30 m2 (The minimum size of suitable habitat).

Shifts in channel morphology can alter the original configuration of a backwater. Additions of subtractions
to the surface area to a backwater habitat were not considered detrimental so long as other minimum habitat
requirements were not violated.

6.1.2 Chemical Habitat Criteria

Wintertime changes in the chemical characteristics of a backwater were primarily related to changes in
temperature and dissolved oxygen.

Minimum temperature requirements for backwater habitats were set at -OSC. Supercooled water below minus
OSC is near the freezing point depression ('d') of most freshwater teleosts (modern bony fishes)(Lagler et a1.
1962). Freezing point depression is a measure of the solute content of a solution, and hence its water
diffusion pressure through tissue membranes. Most freshwater teleosts have a 'd' for blood and plasma of
about -O.570C, which means that body temperature (water temperature) below minus OSC may cease water
diffusion in the circulatory system, and lead to the death of the fish .

Ice formation can isolate backwaters or reduce water exchange with the mainchanne1. This reduction in water
circulation can cause reduced dissolved oxygen levels as O2 is depleted in the stagnant water of the habitat.
No information on dissolved oxygen tolerance limits for Colorado squawfish were found, so general limits
reported for Ictalurids (catfishes) and Centrarchidids (sunfishes) were used. Culture guidelines for
Centrarchids suggest maintaining oxygen concentrations above 5 mg/L with concentrations near 1.0 mg/L being
avoided and potentially fatal (Whitmore et a1. 1960; Moss and Scott 1961; Bonn et al. 1976; Piper et al. 1982;
and Stickney 1986). Information on catfish is similar with minimum concentrations of 5.0 mg/L (Tucker 1985)
and letballevels near 1.0 mg/L (Moss and Scott 1961). For this study dissolved oxygen concentrations below
5.0 mg/L were considered unsuitable habitat for age-O Colorado squawfish.

Table S.

Summary or minimum physical and chemical habitat requirements for
backwaters sampled during the W"mter Ice Study.

Parameter

Minimum Value

Physical Parameters
Surface Area
Free Water Depth
Chemical Parameters
Temperature
Dissolved Oxygen

30 m2

0.3 ft (9.0 em)

-OSC

5.0 mg/I

6.2 WINTER CONDITIONS WITHIN BACKWATER HABITATS

This section provides an outline of winter conditions in 14 backwaters sampled during the first winter ice
measurement trip (January 31 - February 4, 1994) and second measurement trip (February 21 - 24, 1994).
Descriptions of winter habitat conditions in each backwater is presented by reach. A brief synopsis of river
ice conditions for each reach is provided (see Ice Conditions section for detailed description). Table 6 is a
summary of ice thickness, depth of free water, temperature and dissolved oxygen for winter ice measurement
Trips I and IL

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