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. . Area Manager DRAFT 37 eradication program, and physical changes associated with the dam, wild pikenUnnow have been eliminated from the upper San Juan River, both upstream of Navajo Dam as well as at least 25 river miles downstream of the dam (because of cold water temperature). Between 1987 and 1996, no wild pikeminnow adults were caught above Shiprock (approximately RM ISO). Radiotelemerty studies conducted from 1991 to 1995 indicated that pikeminnow remain within a relatively small area of the river, between RM 110 to RM 142 (Holden 2000). However, pikeminnow captures now have extended upstream as far as the PNM weir (RM 166). During the seven-year research period (1991 to 1997) it was estimated that there were fewer than 50 adults in a given year (Ryden 2000a). Razorback sucker From 1991 - 1997, no wild adult razorback suckers were collected in the San Juan River and only one was caught during studies conducted in the late 1980s (Holden 2000). Beginning in May 1987, and continuing through October 1989, complernentary investigations of fishes in the San Juan River were conducted in Colorado, New Mexico, and Utah (Platania 1990; Platania et al. 1991). In 1987, a total of 18 adult razorbacks were collected on the south shore of the San Juan arm of Lake Powell (Platania 1990; Platania et al. 1991). These fish were captured near a concrete boat ramp at Piute Farms Marina and were believed to be either a spawning aggregation or possibly a staging area used in preparation for migration to some other spawning site. Of the 12 razorbacks handled in 1987, eight were running ripe males while the other four specimens were females that appeared gravid. In 1988, a total of 10 razorback suckers were handled at the same general location, 5 of which were in reproductive condition (Platania et al. 1991). Six of the ten individual specimens in the 1988 samples were recaptures from 1987. Also in 1988, a single adult tuberculate male razorback sucker was captured in the San Juan River near Bluff, Utah (RM 80) (Platania 1990, Platania et al. 1991). This was the first confirmed record of this species from the main stem San Juan River. The presence of this reproductively mature specimen suggested that razorback suckers were attempting to spawn within the riverine portion of the San Juan drainage. However, no wild razorback suckers have been collected on the San Juan River since 1988 (Dale Ryden, Service, pers. comm., 2002). A Schnabel multiple-census population model estimated that there were 268 razorback sucker in the San Juan River from RM 158.6 to 2.9 in October 2000 (Ryden 2001). Factors affecting the species environment within the action area Navajo Dam was completed in 1963. Dams have many effects on the physical and biological components ofa stream ecosystern (Williams and Wolman 1984). Some of these effects include a change in water temperature, a reduction in lateral channel migration, channel scouring, blockage offish passage, transformation of riverine habitat into lake habitat, channel narrowing, changes in the riparian community, diminished peak flows, changes in the timing of high and low flows, and a loss of connectivity between the river and its flood plain (e.g., Sherrard and Erskine 1991, Power et al. 1996, Kondolf 1997, Polzin and Rood 2000, Collier et al. 2000, Shields et al. 2000). Of these, change in water temperature, blockage offish passage, transformation of riverine habitat into lake habitat, and changes in the timing and magnitude of