2010-11-22_REVISION - M2009023 (7)

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Outside of the spawning season, adult razorback suckers occupy a variety of shoreline and main channel habitats including slow runs, shallow to deep pools, backwaters, eddies, and other relatively slow velocity areas associated with sand substrates (Tyus 1987; Tyus and Karp 1989; Osmundson and Kaeding 1989; Valdez and Masslich 1989; Osmundson and Kaeding 1991; Tyus and Karp 1990, Holden 1999; Ryden 2000b). Habitat requirements of young and juvenile razorback suckers in the wild are not well known, particularly in native riverine environments. Prior to 1991, the last confirmed documentation of a wild razorback sucker juvenile in the Upper Basin was a capture in the Colorado River near Moab, Utah (Tabs et al. 1965). In 1991, two early juvenile (36.6 and 39.3 mm TL) razorback suckers were collected in the lower Green River near Hell Roaring Canyon (Gutermuth et al. 1994). Juvenile razorback suckers have been collected in recent years from Old Charley Wash, a wetland adjacent to the Green River (Modde 1996). Between 1992 and 1995 larval razorback suckers were collected in the middle and lower Green River and within the Colorado River inflow to Lake Powell (Muth 1995). No young wild razorback suckers have been collected in recent times in the Colorado River or San Juan River. / Population Dynamics / Between March of 1994 and November 2002, a total of 6,861 hatchery raised razorback suckers were stocked into the San Juan River (Ryden 2001; USFWS, unpublished data). Some fish that were stocked as early as 1994 are still being collected during annual sampling (Ryden 2001). A Schnabel multiple-census population model estimated that there were 268 razorback sucker in the San Juan River from RM 158.6-2.9 in October 2000 (Ryden 2001). Larval razorback suckers were collected in 1998, 1999, 2000, and 2001 indicating that the stocked fish are successfully spawning in the San Juan River (Ryden 2001; USFWS, unpublished data). In addition, in 2000 and 2001 larval razorback sucker were collected upstream of the only known spawning site, indicating that spawning is occurring at more than one location in the San Juan River (Ryden 2001; USFWS, unpublished. data). In 2003, two juvenile (age-2) razorback sucker, 249. and 270 mm (9.8 and 10.6 in), thought to be wild-produced were collected in the lower San Juan River (RM 35.7 and 4.8) (Ryden, USFWS, in litt. 2004). Analysis of Species/Critical Habitat Likely to be Affected In the San Juan River subbasin, small concentrations of wild razorback suckers have been reported at the inflow area in the San Juan arm of Lake Powell, Utah (Meyer and Moretti 1988), and one specimen was captured in the San Juan River near Bluff, Utah, in 1988 (Platania 1990, Platania et al. 1991). Two specimens were also collected from off-channel ponds in 1988 (Platania 1990). In Bestgen (1990) additional captures of small numbers of razorback suckers also were reported from the Dirty Devil and Colorado River arms of Lake Powell. Beginning in May 1987, and continuing through October 1989, complementary 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 (six recaptures) 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 14