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filiculoides), duckweed (Lemna sp.), pondweed (Potamogeton sp.), aquatic buttercup (Ranunculus aquatilis), and elodea (Elodea canadensis). Under natural conditions, these plants cover approximately 50% to 75% of the stream surface area. The plants typically grow out from the sides in the main channel, forming dense beds along the stream margins which delineate a small chute of swift flowing water in the center of the channel. In the backwater areas with zero water velocities, vegetation covers nearly 100% of the surface area. There is a limited die-off of vegetation beds during the winter, but most of the beds persist due to the thermal characteristic of the headsprings. The hatchery has a continuing problem with impingement and entrainment of aquatic vegetation which obstructs their water intake and raceway screens. The water intakes divert the entire flow for hatchery operations and constitute the barriers which isolate the Owens tui chubs from hybrids that exist downstream (Fig. 2). To remedy this problem, hatchery personnel, until recently, had been periodically removing nearly 100% of the vegetation from both springs. This consequently rendered the entire habitat devoid of aquatic vegetation for several weeks after removal. The purpose of this study was to investigate the nature of the relationship between the Owens tui chub and aquatic vegetation so that recovery actions could be identified and implemented, and to identify impacts caused by hatchery procedures so that these procedures could be modified. Although life history information has been documented for other subspecies of tui chub inhabiting similar environments (Cooper 1978; Kimsey 1954; Vicker 1973; Bird 1975; Kucera 1978) and for the tui chub as a species (Burns 1966; Moyle 1976), life history and ecological requirements of the Owens tui chub have not been investigated. Life history and population data from limited California Department of Fish and Game observations are primarily in the form of unpublished memoranda and correspondence. Most of what is known of this fish concerns taxonomy and distribution (Gilbert 1893; Snyder 1917; Miller 1969, 1973). Aquatic vegetation is an important habitat component for several subspecies of tui chub (Moyle 1976). Lahontan tui chub are opportunistic generalist feeders and an integral part of their diet consists of aquatic plants and invertebrates associated with aquatic plants (Kimsey 1954). Both Mohave tui chub (G. b. mohavensis) and the Lahontan tui chub utilize aquatic vegetation as a spawning substrate. (Kimsey 1954; Vicker 1973; Cooper 1978). 15