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I I I I I I I I I I I I I I I I I I I 001611 Evaluation of habitat as a limiting factor was a complex issue requiring a variety of biological and physical studies. The biological studies investigated the habitats that the fishes used and attempted to determine which habitats were key for their success. Spawning habitat and nursery habitat were generally considered key habitats for the two endangered fish species because lack of recruitment was a major factor influencing the fishes' endangered status (Minckley et al. 1991, Tyus 1991), and their spawning and nursery habitats were relatively rare and flow dependent. Physical studies were needed to describe the key habitats, determine their availability, determine their quality, and determine if habitat quantity and quality improvements in the San Juan River were needed. Key habitats may be in short supply, too poor in quality, or not available at the right time of year. This section describes how the SJRIP studies determined key habitats, key habitat availability, and key habitat quality for each of the two endangered species. Also presented are management actions taken to maximize key habitat quality and quantity. Habitat Use Colorado Pikeminnow Studies in the Green and Colorado rivers during the 1970s and 1980s identified the major life history components of Colorado pikeminnow. Adults migrated during early summer, often over 200 miles, to two major spawning areas in the Green River (Tyus 1985, 1990, 1991). Young hatched in a matter of days and drifted downstream to suitable backwater nursery habitats (Haynes et al. 1984, Nesler et al. 1988). Young-of-the-year were found in backwaters in the fall (Holden 1977, Tyus and Haines 1991). Because of sampling inefficiencies, and perhaps low population numbers, 2-, 3-, and 4-year-old Colorado pikeminnow were seldom collected (Holden and Stalnaker 1975, Tyus and Haines 1991), so their habitat use is poorly understood. These efforts led to research focused on two key habitats: spawning areas and backwaters. Chapter 3 of the Flow Report (Converse and Holden 1999) summarizes what is known about the life history and habitat use of this species. The following highlights San Juan River habitats used by this species and those habitats that became the focus of studies. Adults Adult Colorado pikeminnow habitat use in the San Juan River was studied primarily through radiotelemetry. From 1991 to 1994, 13 adult Colorado pikeminnow were captured, radio-tagged, and followed, both on the ground (from shorelines and boats) and in the air (Ryden 2000a, Ryden and Ahlm 1996). Fish capture locations, along with 236 subsequent radiotelemetry contacts, provided information on portions of the river used, movements, likely spawning locations, and specific habitat use. Most of the fish remained within a relatively small area of the river (Figure 3.1), from about RM 109 to RM 142 (Figure 2.1). This 33-mile reach included the "Mixer" (RM 129.8 to RM 133.4), an area of structural complexity and numerous secondary channels. Only one of the 13 radio-tagged fish was found outside this 33-mile reach, a large female captured and tagged near Bluff, Utah. This fish remained in the area ofRM 73 to RM 76, except in 1994 when September 2000 3-3 Program Evaluation Report