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Methods The 60 Ian of river extending from the tailrace of Davis Dam (RM-82, Fish-n-Map Comp.) to Catfish Bay (RM-25) was sampled during a four-year period (1999-2002) (Figure 1.1). Surveys were conducted between the months of December and May when both sucker species spawn. Working during the winter and early spring also avoided conflicts with recreationalists that visit the area during the summer. Trammel nets were used to minimize fish stress and mortalities. Net lengths and mesh sizes varied in order to capture all life stages of fish. Nets were 2 m deep and lengths ranged from 25 to 50 m. Three mesh sizes were used, 1.2, 2.5, and 3.8-cm. Nets were generally set off jetties and in backwaters where currents were mild and nets were less apt to collect debris. Sampling occurred at night with nets set just prior to dusk and pulled at dawn. Initial surveys conducted in 1999 and 2000 sampled approximately every 3 kIn along the 60 kIn reach. During these cold months, we found that the vast majority of fish were concentrated into off-channel habitats such as Davis Dam tailrace, Laughlin Lagoon, Boy Scout Camp, Park Moabi, Golden Shores, Pulpit Rock, Tampas Wash, Blankenship Bend and others. Sampling in 2001 and 2002 focused on locations where fish were found concentrated. Biweekly sampling surveys were based out of Big Bend State Park in Laughlin, Nevada, and Park Moabi, California. When adequate help was available, two survey crews worked both sites. When only one crew was available, they worked Park Moabi during January through early March and the Laughlin area from February through April. Fish data included: gear type, location, species, total length, weight, and sexual condition. Native fish were implanted with a passive integrated transponder (pIT) that allowed us to identify individual fish. Recapturing these marked fish provided information pertaining to growth, movement, and population size. Collections did result in some net mortality. Fin rays, vertebrae, and otoliths were collected for the netting mortalities to age flannelmouth suckers. Global Positioning System (GPS) coordinates were taken for all razorback suckers, bonytail, and for flannelmouth suckers collected in California waters as requested by the state. Sampling in the main channel proved impractical due to water depth (3 m) and currents. A method of visually surveying fish from a boat was developed and standardized. We used time intervals of 15 minutes (fish #/15 minutes), similar to electrofishing and used a GPS to measure the distance we traveled. Only fish observed within 10m of either side of the boat were counted to standardize our survey width. A member of the crew would stand on the bow and count fish while another kept record. We idled downstream at about 6 lan/hour. Standing crop was calculated based on fish/m2 and kg/m2. Populations were estimated based on the river's surface area ofthe river reach. Light traps were used in 2000,2001, and 2002 to help identify when and where spawning was taking place. Quatrefoil, Plexiglas traps were equipped with internal lights that attracted fish into the trap. Traps were generally set along shore at dusk and collected at dawn. Samples were generally examined in the field. Larval fish were removed and preserved for laboratory analysis. Larval sucker identification was verified by the Larval Fishes Laboratory, Fort Collins, Colorado, and through voucher specimens. Results and Discussion Passive Netting More than 8,000 fish were collected during the 4-year effort (Table 1.1). Nineteen species (3 native, 16 introduced) were represented. Due to the successful introduction of flannelmouth sucker, native species (flannelmouth and razorback sucker) made up 40% ofthe catch in the Laughlin area. A total of238 razorback sucker, 1,355 flannelmouth suckers, and 1 bonytail were captured. 3