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<br />c..., <br />C"l <br />1-. <br />00 <br />-.J <br /> <br />~0 <br />...,. <br /> <br />Evaluation of habitat as a limiting factor was a complex issue requiring a variety ofbio]ogical and physical <br />studies. The biological studies investigated the habitats that the fishes used and attempted to determine <br />which habitats were key for their success. Spawning habitat and nursery habitat were generally considered <br />key habitats for the two endangered fish species because lack of recruitment was a major factor influencing <br />the fishes' endangered status (Minckley et al. ]99], Tyus ]99]), and their spawning and nursery habitats <br />were relatively rare and flow dependent. Physical studies were needed to describe the key habitats, <br />determine their availability, determine their quality, and determine if habitat quantity and quality <br />improvements in the San Juan River were needed. Key habitats may be in short supply, too poor in quality, <br />or not availab]e at the right time of year. This section describes how the SJRIP studies determined key <br />habitats, key habitat avai]ability, and key habitat quality for each of the two endangered species. Also <br />presented are management actions taken to maximize key habitat quality and quantity. <br /> <br />Habitat Use <br /> <br />Colorado Pikeminnow <br />Studies in the Green and Colorado rivers during the 1970s and 1980s identified the major life history <br />components of Colorado pikeminnow. Adu]ts migrated during early summer, often over 200 miles, to two <br />major spawning areas in the Green River (Tyus 1985,1990,1991). Young hatched in a matter of days <br />and drifted downstream to suitable backwater nursery habitats (Haynes et a]. 1984, Nes]er et al. 1988). <br />Y oung-of-the-year were found in backwaters in the fall (Ho]den 1977, Tyus and Haines 1991). Because <br />of sampling inefficiencies, and perhaps low population numbers, 2-, 3-, and 4-year-o]d Colorado <br />pikeminnow were seldom collected (Ho]den and Stalnaker 1975, Tyus and Haines 1991), so their habitat <br />use is poorly understood. These efforts led to research focused on two key habitats: spawning areas and <br />backwaters. Chapter 3 of the Flow Report (Converse and Ho]den 1999) stunmarizes what is known <br />about the life history and habitat use of this species. The following highlights San Juan River habitats used <br />by this species and those habitats that became the focus of studies. <br /> <br />Adults <br />Adult Colorado pikeminnow habitat use in the San Juan River was studied primarily through <br />radiotelemetry. From ]991 to 1994, 13 adult Colorado pikeminnow were captured, radio-tagged, <br />and followed, both on the ground (from shorelines and boats) and in the air (Ryden 2000a, Ryden <br />and AhIm 1996). Fish capture locations, along with 236 subsequent radiotelemetry contacts, provided <br />information on portions of the river used, movements, likely spawning locations, and specific habitat use. <br />Most of the fish remained within a relatively small area of the river (Figure 3.1), from about RM 109 <br />to RM 142 (Figure 2.1). This 33-mile reach included the "Mixer" (RM 129.8 to RM 133.4), an area of <br />structural complexity and numerous secondary channels. Only one of the 13 radio-tagged fish was <br />found outside this 33-mi]e reach, a large female captured and tagged near B]uff, Utah. This fish <br />remained in the area of RM 73 to RM 76, except III 1994 when <br /> <br />September 2000 <br /> <br />3-3 <br /> <br />Program Evaluation Report <br />