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<br />196
<br />
<br />The Southwestern Naturalist
<br />
<br />vol. 33, no. 2
<br />
<br />TABLJ:: 2-Cumulative, 8-day morality for all cold shock temperatures in 1984 and 19115. The
<br />1985 data, where 150 fish were used, were multiplied by \.33 to compare with the 19114
<br />experiment where 200 fish were used.
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<br />Ab,upl Yea,
<br />!l'rnp.',alu,,' .IUK"k ("C) 1981 1985 TOlal
<br />0 58 2 60
<br />-5 49 4 53
<br />-10 63 2 65
<br />-15 130 131 261
<br />Total 300 139
<br />
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<br />temperature drops sudden~y below lOoC during embryonic development
<br />(Hassler, 1970).
<br />These bioassay results emphasize the need to assess temperature
<br />conditions in critical habitats. Cold shock duration and severity in field
<br />situations would depend on the location of drifting larvae and hydrological
<br />conditions in the mixing zone. When abrupt shocks are possible, my data
<br />might be used to suggest the boundaries of sa[e_~per~t!9E. .oL~~ter:l:lse._
<br />projects that affect water temperaMeJ."n-Coloratlo squawfish spawning and
<br />nursery areas. Water temperatures below major Colorado River dams
<br />(Flaming Gorge, Glen Canyon) are usually <120C (Vanicek and Kramer,
<br />1969; Marsh, 1985), which is 8 to lOoC below the temperature at which
<br />squaw[ish larvae are probably hatched (Haynes et a1., 1984). Discharges
<br />from epilimnetic penstocks could be scheduled to avoid shocking larvae
<br />drifting [rom tributary spawning areas like the Yampa River (Haynes et a1.,
<br />1984; Tyus and McAda, 1984).
<br />The similarity in temperature response between geographical populations
<br />of other fish (Mathur et aI., 1983) may also hold for the endemic Colorado
<br />River species. Immature Colorado squawfish, humpback chub (Gila cypha),
<br />bony tail chub (G. elegans), and razorback sucker (Xyrauchen texanus) have
<br />similar final temperature preferenda (Black and Bulkley, 1985b). Therefore,
<br />these data on cold shock effects on Colorado squaw fish might provide
<br />general guidelines for other endemic Colorado River fish as well.
<br />
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<br />
<br />Funding for this project was provided by the U. S. Fish and Wildlife Service (Contract Number
<br />14-16-009-1501-W05). U, S. Fish and Wildlife Service Biologists H,Tyus~ R.Jones, B. Jensen, and
<br />D. Archer cooperated, V. Rosen conducted most o{ the labOT~l~~ye;(p~~i~ents, and L. Tucker
<br />counseled on statistical analysis. The Cooperative Unit is supported by the U, S. Fish and
<br />Wildlife Service, Utah State University, and the Utah Division o{ Wildlife Resources.
<br />
<br />LITERA TV RE CITED
<br />
<br />ALLANSON, B. R., A. BOK, AND N. I. VANWYK. 197\. The influence of exposure to low
<br />temperature on Tilapia mossambica Peters. (Cichlidae), II. Changes in serum osmolarity,
<br />sodium and chloride ion concentrations. J. Fish BioI., 3:181-185.
<br />BLACK, T., AND R. V. BULKLEY. 1985a. Growth rate of yearling Colorado squawfish at diUerent
<br />water temperatures. Southwestern Nat., 30:253-257.
<br />_, 19115b. Preferred temperature of yearling Colorado squaw fish, Southwestern Nat.,
<br />30:95-100.
<br />BURT~N, D. T., P. R. ABELL, AND T. P. CAPAZZI. 1979. Cold shock: eHect of rate of thermal
<br />decrease on Atlantic menhaden. Mar. Pollut. Bull., 10:347-349.
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