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River (Burdick et al. 1997) but artificial cover could be placed on the gravel substrates of such ponds. Juvenile razorback suckers readily use rooted aquatic vegetation as cover in the Lower Colorado River Basin based on SCUBA observations (G. Mueller and T. Burke, 1994, personal communication). Aquatic vegetation in Leota Bottoms and Old Charley Wash may have been a factor in the survival of Age-O razorback suckers. Abundant red shiners in Old Charley Wash were captured in open water so they would were spatially separated from the larval and juvenile razorback suckers that used vegetative cover in the littoral zone (Modde 1997). Sonic-tagged subadult razorback suckers stocked into Lakes Mohave and Powell quickly occupied backwaters with cover (Mueller and Marsh 1998). In Lake Mohave, 40% of the fish used Saqo pondweed as cover and about 14% used cavities in rubble and cobble substrates. In Lake Powell, a high percentage (up to 86\) of the fish used flooded Tamarisk as cover. Some recruitment of razorback suckers was documented in Lake Mead where fish between 318 and 381 mm TL (one dead fish was determined to be 4 years old) were captured (P.B. Holden, 1998, personal communication) . Holden attributed the recruitment of razorback suckers in Lake Mead to higher densities of zooplankton, presence of more cover as rooted aquatic vegetation and flooded Tamarisk, and stable water levels, compared to Lake Mohave where such conditions do not exist and recruitment has not occurred. If management of the nonnative minnows, green sunfish, channel catfish, smallmouth bass, and juvenile largemouth bass is possible in the general vicinities of enhanced or restored floodplain habitats (particularly downstream to reduce numerous nonnative fishes in backwaters), razorback suckers may be able to develop self-sustaining populations. However, the size attained by razorback suckers is only about 25 mm TL in 8 weeks (Figures 1 and 2). The body of a 25 mm razorback sucker is deep and wide enough to preclude predation by adult red shiner based on the gape size of adult red shiner mouths (T. Crowl, 1995, personal communication). A razorback sucker of 25 mm may still be vulnerable to fathead minnows since these minnows tear their prey apart and eat the pieces (Dunsmoor 1993). In addition, razorback larvae of 25 mm as well as larger juveniles would still be highly vulnerable to predation by juvenile and adult green sunfish, channel catfish, smallmouth bass, and largemouth bass. D. Caotive Propaqation/Stockinq of Razorback Suckers. The razorback sucker was considered the highest priority species for propagation among the four endangered Colorado River fishes by the Biology Committee (Wydoski 1994) because the stocks are declining and little or no recruitment has been documented for this species in the Upper Colorado River Basin. A dramatic decline in razorback suckers occurred between 1974 and 1991 in RK 245.9-297.8 (RM 152.8-185.1) of the upper Colorado River (Burdick 1992). A high capture of 206 razorback suckers in this reach during 1974 declined and no fish were captured during 1989-1992. Three adult razorback suckers were captured in this reach in 1993, one in 1995, and none in 1996 and 1997 (C. McAda, 1998, personal communication). The Recovery Program Biology Committee also agreed that augmentation stocking was required in the middle Green River to increase and stabilize the present population (Wydoski 1994) that is estimated to be about 500 razorback suckers (Modde et al. 1996). Captive propagation and stocking of razorback suckers should be considered a fishery management tool and not a solution to recovery. Captive propagation and stocking are needed to (1) reestablish or augment stocks in Upper Basin rivers until other problems are solved, (2) accelerate the rate of recovery, and (3) have fish in the rivers to evaluate various recovery actions. Ultimately, the integrity of river- 36 I I I I I I I I f fl ~ I J J , 1 J 1 J