Final Programmatic Biological Opinion for Bureau of Reclamation's

A marked decline in populations of razorback suckers can be attributed to construction of damsand reservoirs, introduction of nonnative fishes, and removal of large quantities of water from theColorado River system. Dams on the mainstem Colorado River and its major tributaries havesegmented the river system, blocking migration routes. Dams also have drastically altered flows,temperatures, and channel geomorphology. These changes have modified habitats in many areasso that they are no longer suitable for breeding, feeding, or sheltering. Major changes in speciescomposition have occurred due to the introduction of numerous nonnative fishes, many of whichhave thrived due to man-induced changes to the natural riverine system.Critical habitat was designated in 1994 within the 100-year floodplain of the razorback sucker'shistorical range in the following area of the upper Colorado River (59 F.R. 13374). The primaryconstituent elements are the same as critical habitat for Colorado pikeminnow describedpreviously.Colorado, Mesa and Garfield Counties. The Colorado River and its 100-year floodplainfrom Colorado River Bridge at exit 90 north off Interstate 70 in T. 6 S., R. 93 W., section16 (6th Principal Meridian) to Westwater Canyon in T. 20 S., R. 25 E., section 12 (SaltLake Meridian) including the Gunnison River and its 100-year floodplain from theRedlands Diversion Dam in T. 1 S., R. 1 W., section 27 (Ute Meridian) to the confluencewith the Colorado River in T. 1 S., R. 1 W., section 22 (Ute Meridian).Colorado, Delta and Mesa Counties. The Gunnison River and its 100-year floodplainfrom the confluence with the Uncompahgre River in T. 15 S., R. 96 W., section 11 (6thPrincipal Meridian) to Redlands Diversion Dam in T. 1 S., R. 1 W., section 27 (UteMeridian).Utah, Grand, San Juan, Wayne, and Garfield Counties. The Colorado River and its100-year floodplain from Westwater Canyon in T. 20 S., R. 25 E., section 12 (Salt LakeMeridian) to full pool elevation, upstream of North Wash, and including the Dirty Devilarm of Lake Powell in T. 33 S., R. 14 E., section 29 (Salt Lake Meridian).Status and DistributionThe current distribution and abundance of the razorback sucker have been significantly reducedthroughout the Colorado River system, due to lack of recruitment to the adult population (McAda1987; McAda and Wydoski 1980; Holden and Stalnaker 1975; Minckley 1983; Marsh andMinckley 1989; Tyus 1987). The only substantial population exists in Lake Mohave with anestimated population of 25,000 adult razorback suckers in 1995 (Chuck Minckley pers. com.)down from an earlier estimate of 60,000 adult razorback suckers (Minckley et al. 1991). They donot appear to be successfully recruiting. While limited numbers of razorback suckers persist inother locations in the lower Colorado River, they are considered rare or incidental and may becontinuing to decline.29