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Chironomid larvae appear to be the most important food <br />item. They were present in all four samples and in 27 of the 35 <br />digestive tracts examined. They had the highest I.R.I. value in <br />three of the four samples and third highest in one. Other items <br />of importance include: larvae of two species of hydroptillid <br />caddisfly, other aquatic invertebrates, plant material, and <br />detritus. Chironomid larvae, caddisfly larvae, and detritus were <br />present in all four samples, indicating that they are available <br />year-round (Fig. 6). <br />An examination of plant material collected from the CD <br />headspring showed that most of the invertebrate food items were <br />present in the vegetation, chironomid larvae being the most <br />abundant and profuse. This finding indicates that aquatic <br />vegetation is not only an important food source, but also <br />provides an important substrate which supports the aquatic <br />invertebrate fauna of the headsprings. <br />These experiments and observations suggest that aquatic <br />vegetation is an important ecological component of the <br />headsprings. Another outstanding component, and one that is <br />highly interrelated, is the constancy of this environment, <br />primarily flow and temperature. Environmental constancy, among <br />other things, allows for the persistence of the vegetation <br />through the winter, as well as a year-round production of the <br />aquatic invertebrate fauna. Any management or recovery plan for <br />the Owens tui chub in these headsprings should recognize the <br />importance of these two ecological components. <br />LITERATURE CITED <br />Bailey, R. A., G. B. Dalrymple, and M. A. Lanphere. 1976. <br />Volcanism, structure, and geochronology of Long Valley <br />Caldera, Mono County, California. J. Geophysical Research. <br />81(5):725-744. <br />Bird, F.H. 1975. Biology of the blue and tui chubs in East and <br />Paulina Lakes, Oregon. M. S. thesis, Oregon State Univ, <br />Corvalis. 165 p. <br />Burns, J. W. 1966. Tui chub. Pages 528-530 in A. Calhoun, ed. <br />Inland Fisheries Management. Calif. Dept. Fish Game. 546 p. <br />Castleberry, D. T. 1985. The physiological responses of an <br />endangered fish (Gila bicolor mohavensis) and its competitor <br />(Gila orcutti) to environmental stressors. Masters <br />thesis. Univ. Calif. Davis. 35 p. <br />Cooper, J. J. 1978. Contributions to the life history of the <br />Lahontan tui chub, Gila bicolor obesa (Girard), in Walker <br />Lake, Nevada. Masters thesis, Univ. Nevada, Reno. 88 p. <br />. 1982. Observations on the reproduction and embryology <br />of the Lahontan tui chub, Gila bicolor, in Walker Lake, <br />Nevada. Great Basin Naturalist. 42(1): 60-64. <br />22