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V MANAGEMENT BRIEFS Methods Telemetric transmitters were externally attached to 120 razorback suckers that were stocked at three different locations: (1) areservoir, (2) a small (<1- ha) backwater connected to the Green River, Utah, and (3) a large (30-ha) backwater (Laughlin La- goon, Nevada) connected to the lower Colorado River. Thirty fish were released in both the res- ervoir and small backwater, and 60 were released in the large-backwater test. Their movements were followed for 28 d. Reservoir and small-backwater tests were sub- divided into two 15-fish subgroups; one group was released (reference) after being acclimated to wa- ter conditions and the second was site-acclimated for 3 d behind a barrier net (6-mm mesh) before release. The large-backwater test was divided into four subgroups of 15 fish each: (1) pond-reared and released immediately (reference), (2) pond- reared and acclimated for 7 d at the site, (3) flow- conditioned and released immediately, and (4) flow-conditioned and site-acclimated for 7 d. Sonic transmitters (70 kHz) were used for the reservoir experiment, and radio transmitters (40- 41 MHz) were used for the small- and large- backwater tests. Transmitters were individually coded (pulses or frequencies) and similar in shape (conical), size (8 mm diameter, 35-50 mm long), weight (4-7 g), and transmitter life (45 d). Radio transmitters had external trailing antennae. Ra- zorback suckers possess a unique cartilaginous dorsal hump suitable for transmitter attachment. Transmitters were externally attached, a process taking about 30 s, to reduce stress and convales- cence associated with abdominal surgery (Mellas and Haynes 1985). Anesthesia was not used, par- tially because it could have impaired swimming performance. The reservoir test was conducted at Lake Pow- ell, a large (65,000-ha) mainstream reservoir on the Colorado River. Reservoir fluctuations typi- cally exceed 15 m annually, which prevents es- tablishment of submergent vegetation. Under- water cover is limited to rock talus Tamarix sp. and sparse flooded salt cedar. Fish were trans- ported by boat on 3 June 1997 and released in Castle Creek Canyon, a large inundated side can- yon of the San Juan Arm of Lake Powell, Utah. The release site was 16 km down-reservoir of the inflow of the San Juan River. Fish were thermally acclimated (1 h), after which the transmitters were attached. Fish were alternately released in front of (reference group) or behind a barrier net 271 enclosure (200 mz), which held the acclimating fish (test group) for 3 d. The small-backwater test was conducted in Mil- lard Canyon, a side canyon of the Green River, Utah, that seasonally floods. Thirty fish were trans- ported by tank truck and raft on 16 June 1998 to the release site located 53 km upstream from the confluence of the Green and Colorado rivers. Both rivers were turbid and confined by steep canyon walls that limited channel widths to typically less than 100 m. Backwater habitat was rare except for small side eddies and side canyon entrances that flood during spring runoff. Water velocities were moderate (about 0.5-1.0 m/s) for both the Green and Colorado rivers upstream of their confluence. However, downstream the Colorado River enters Cataract Canyon, a 26-km white-water reach that extends downstream to Lake Powell. The large-backwater experiment was conducted on the Colorado River downstream of Davis Dam in Arizona and Nevada. Fish were released into Laughlin Lagoon, a 30-ha backwater 12 km down- stream of Laughlin, Nevada. The lagoon is con- nected to the river through a navigational channel and by paired culverts (1 in diameter) located at both ends of the levee. Portions of the lagoon were recently dredged, but 75% of the area is shallow (<1 m) and supports lush stands of submergent pondweed Potamogeton sp. and emergent bullrush Scirpus sp. The river was dredged in the 1950s, and channel widths are typically less than 150 m. Currents appeared similar to those observed in the Green River (<1 m/s), but backwaters and sub- mergent vegetation were more common. Fish for the large-backwater experiment origi- nated from two sources: Willow Beach National Fish Hatchery (WBNFH), where fish are reared in ponded (0.05 m/s recirculating flows) raceways, and Boulder City Municipal Ponds (BCMP), Ne- vada, where fish were maintained in lined earthen ponds (Table 1). Thirty WBNFH fish were placed in a concrete raceway (1.5 X 10 m) on 16 No- vember 2000 and subjected to flow for 2 months. A 10-cm inlet pipe produced flows that varied from 0.1 to 1.0 m/s, depending upon location. On 12 January 2001, radio transmitters were attached to these and 30 fish collected from the BCMP. Half of each group was transported and site acclimated in a 0.5-ha netted embayment at Laughlin Lagoon. The remaining half stayed on site until 19 January (after 7 d), when they to were transported to Laughlin Lagoon. The barrier net was removed and all study fish had access to the river at the same time.