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<br />r <br />, <br />, <br />, <br /> <br /> <br />~ <br />:) <br /> <br />. . <br /> <br />Backwalers which became inundated were not considered usable habitat. Reductions in backwaler size were <br />nOI considered Significanl unless the lotal area became less than 30 m' (The minimum size of suitable habitat). <br /> <br />Shifts in channel morphology can aller the original COnfiguration of a backwater. Additions of subtractions <br />[0 the surface area to a backwater habitat were nOI considered detrimental so long as other minimum habital <br />requirements were not violated. <br /> <br />6.1.2 Cheml.:al Habitat Critcria <br /> <br />Winlertime changes in the chemical characteristics of a backwater were primarily related 10 changes in <br />lemperature and dissolved oxygen. <br /> <br />Minimum temperature requirements for backwaler habitats were set at -O.5"C. Supercooled water below minus <br />O.S"C is near the freezing point depression ('d') of most freshwater teleosts (modern bOny fishes)(LagIer et at <br />1962). Freezing point depression is a measure of the solute content of a solution, and hence its water <br />diffusion pressure through tissue membranes. Most freshwater teleosts ha\'e a 'd' for blood and plasma of <br />abOut -O.57"c, which means that body temperature (water temperature) below minusO.5"C may cease water <br />diffusion in the circulatory S}'Stelll, and lead to the death of the fish . <br /> <br />Ice formation can isolate backwaters or reduce water =1IaDge with the mainchannel. This reduction in water <br />circulation can cause reduced dissolved oxygen levels as 0, is depleted in the stagnant water of the habitat. <br />No information on dissolved oxygen tolerance limits for. Colorado squawfish were found, so general limits <br />feported for IctaJurids (catfishes) and Centrarehidids (sunfishes) were used. Culture guidelines for <br />Cenuarchids suggest maintaining oxygen concentrations above 5 mgIL with concentrations near LO mg/L being <br />avoided and potentially fatal (WhitmOre et aL 1960; Moss and Sant 1961; Bonn et al. 1976; Piper et aL 1982; <br />and Stickney 1986). Information On catfish is silDilarwith minimum concentrations of 5.0 mg/L (TUcker 1985) <br />and lethal levels near 1.0 mg/L (Moss and Scolt 1961). For this study dissolved oxygen concentrations below <br />5.0 mgfL were considered unsuitable habitat for age-O Colorado squawfish. <br /> <br />Table 5. <br /> <br />SllJDlILiI'Y oC mInlmllJD physical and chemJcal bahttat requlI'emenlS Cor <br />bacbalen sampled dDrinl !be WInter Ice SlDdr. <br /> <br />Parameter MlnImam Value <br />Physical Parameters <br />Surface Area 30m' <br />Free Water Depth Q.3 tl (9.0 CIIl) <br />Chemical Parameters <br />Temperature -O.5"C <br />Dissolved Oxygen 5.0 mgtl <br /> <br />6.2 WINTER CONDmONS WlTHIN BACKWATER HABITATS <br /> <br />This section provides an outline of winter conditions in 14 backwaters sampled during the first winter ice <br />measurement trip (January 31 . February 4, 1994) and second measurement trip (February 21 - 24. 1994). <br />Descriptions of winter habitat conditions in each backwater is presented by reach. A brief synopsis of river <br />ice conditions for each reach is provided (see Ice Condilions section Cor derailed description). Table 6 is a <br />summary of ice thickness, depth of free waler, temperatufe and dissOlved oxygen ror winter ice measurement <br />Trips I and II <br /> <br />11 <br />