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<br />March 1984
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<br />Haynes et al.-Larval Colorado Squawfish
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<br />31
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<br />in 1980 and 1981 (Haynes and Muth, in press). Although the frequency of
<br />deformed squawfish is presently undetermined, theJrequency for roundtails
<br />was relatively high e.g. 10.3% and 16.5% in 1980 and 1981, respectively. A
<br />number of different causative factors for lordosis have been implicated
<br />including pesticides, heavy metals, nutritional deficiencies, oxygen and
<br />temperature fluctuations and extremes, genetic aberrations, and disease
<br />(Hickey, 1972; Bengtsson, 1979); however, Haynes and Muth were able to
<br />rule-out disease only. Since deformed age group I roundtails have not been
<br />observed (no juvenile squawfish were collected during the present study),
<br />either the condition was reversible or deformed individuals did not survive.
<br />This suggests that exogenous factors other than flow and temperature
<br />regimes may also be limiting recruitment in Colorado squaw fish. Further-
<br />more, interactions between squawfish and other native and exotic species
<br />(Colorado River Fishes Recovery Team, 1978; Holden, 1979; Behnke and
<br />Benson, 1980) could be playing a critical role in the survival of this rare
<br />species 1980.
<br />
<br />We express our appreCla110n to the following persons who provided field and laboratory
<br />assistance and/or equipment for the conduct of this study: John Cancelosi, John Hawkins,
<br />Robert Hufziger, and Larry Wycoff (Department of Fishery and Wildlife Biology, Colo. State
<br />Univ., Ft. Collins) assisted variously with field collections, sample processing and data reduction.
<br />Darrel Snyder (same affiliation) provided field assistance and confirmations of larval identifica-
<br />tion. Tom Beck and Glenn Smith (Colo. Div. Wildlife) provided field assistance in 1981. Richard
<br />Valdez and Charles McCada (U.S. Fish and Wildlife Ser.) provided field assistance and
<br />equipment. Steven Petersburg and Earl Perry (Dinosaur National Monument) provided unlimited
<br />access to and equipment for Yampa River studies. Don Hays, Carl Lesher, and Robert Ugland
<br />(U.S. Geol. Sur.) provided unpublished flow and temperataure data.
<br />
<br />LITERATURE CITED
<br />
<br />ANONYMOUS. 1975. Colorado River regional assessment study. Part one: executive summary,
<br />basin proHle, and report digest. Utah Water Res. Lab., Utah State Univ., Logan. Prep.
<br />for Nat. Comm. on Water Qual., Contract No. WQ5AC05A.
<br />BEAMESDERFER, R. C. AND T. C. BJORNN. 1980. Habitat selection, spawning behavior and early
<br />life history of Northern squaw fish with inferences to Colorado squawfish. Idaho Coop.
<br />Fish. Res. Unit, Univ. of Idaho, Moscow. Prog. Rep. to Colo. River Fish. Proj., U.S.
<br />Fish and Wildlife Ser., Sail Lake City, Utah. (unpubl., mimeo).
<br />BEHNKE. R. J. AND D. E. BENSON. 1980. Endangered and threatened fishes of the upper
<br />Colorado River basin. Coop. Ext. Ser., Colorado State Univ., Ft. Collins, Colorado,
<br />Bull. 503A.
<br />BENGTSSON, B. -E. 1979. Biological variables, especially skeletal deformities in fish, for
<br />monitoring marine pollution. Phil. Trans. R. Soc. Lond. B., 286:457-464.
<br />CARLSON, C. A., C. G. PREWITT, D. E. SNYDER, E. J. WtCK, E. L. AMES AND W. D.
<br />FRONK. 1979. Fishes and macroinvertebrates of the White and Yampa rivers. Colorado.
<br />BLMBiol. Sci. Ser., 1. Denver.
<br />CoLOUDO RIVER FISHES RECOVERY TEAM. 1978. Colorado squawfish recovery plan. U.S. Fish
<br />and Wildlife Service.
<br />CUSHMAN, R. M., S. B. GOUGH, M. S. MORAN AND R. B. CRAIG. 1980. Sourcebook of
<br />hydrological and ecological features. Water resource regions of the conterminous United
<br />States. Ann Arbor Sci. Pub. Ine., Ann Arbor.
<br />DEACON J. E., G. C. KOBETICH, J. D. WILLIAMS AND S. CoNTRERAS. 1979. Fishes of North
<br />America endangered, threatened, or of special concern 1979. Fisheries. 4:29-44.
<br />DE VUMING, V. L. 1972. Environmental control of teleost reproductive cycles: a brief review.
<br />J. Fish. BioI., 4:131-140.
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