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20 I I I I I I I I I I I I I I I I I I I Usually two netters dipped the fish from the bow of the raft, but at times only one netter was used. The actual electrofishing time was recorded for each sample directly from the timer on the WP-15 in order to compute catch per unit effort (CPE) for each species within each sample. An average CPE (number of fish caught per 10 hours of actual electrofishing time) was then calculated for each species using the CPE's of each sample, including zeros, where the species was not captured in a given sample. All netted endangered fish as well as the native f1annelmouth and bluehead suckers, roundtail chub and game species such as st.riped bass and walleye were measured and weighed. 3.3.2 Gill and Trammel Nets Gill and trammel nets were used to sample adults and juveniles in eddies, pools, and slow runs (Photo A-42). Five mesh sizes of gill nets were used, including 1.5, 2.0, and 2.5-inch mesh, as well as a net with large floats for surface sets, and experimental gill nets. The experimental nets yielded numerous small chubs of a size not captured by other nets and proved most valuable in assessing size distribution. The trammel nets used were 50 feet long, 5 feet deep, and had 1.5-inch inside bar mesh and 10.0-inch outside mesh. All the nets were set and retrieved from the 17-foot Havasu raft or the 17-foot Achilles. When water temperature was warmest (>200c) in July and August, each net was set for no longer than 2 hours to minimize st.ress on the netted fish. After temperature cooled in September and October (<200c), some nets were set for up to 4 hours. CPE was computed for each species for each sample as the number of fish caught per 100 linear feet of net per 100 hours. Average CPE was then calculated using the CPE's for each species from each sample, including zeros, where the species was not captured in a given sample. 3.3.3 Seines Small-mesh seines were used to sample larvae, YOY, and juveniles primarily in backwaters, shorelines, isolated pools, and small eddies. The seines were 10 feet long and 4 feet deep, with either 1/16 or 1/8-inch delta mesh (Photos A-43 and A-44). The smaller mesh seine was used when larvae and small YOY were present, and the larger mesh seine was used following the growth of these fishes. The surface area seined by each sample effort was measured and the CPE was computed for each species as the number of fish per 100 square meters of area sampled. An average CPE was computed for each species using the CPE's from each sample, including zeros, where the species was not captured in a given sample. 3.3.4 Kick Screens Kick screens were used in a few concavities and isolated pools where seines could not be used. Each screen consist.ed of a 4-foot length of 1/32-inch mesh screen tacked to two hand-held brailes. No CPE st.atistics were computed for this gear. 3.3.5 Drift Nets Larval drift nets were used to capture larvae and YOY being transported downstream by river currents. These fine-mesh nets were designed from the prototypes developed by Haynes et at (1985). Each net was 10 feet long with a 12 by 18-inch opening (Photos A-45 through A-48). The mesh was 560 micron Nitex plankton netting. Drift nets were placed in sets of four in water 3-4 feet deep along the shoreline. Most sets were left in the water for only 15 to 20 minutes to prevent clogging and backup from the large volume of detritus carried by the river. A Marsh-McBirney current meter was used to determine average velocity at the mouth of each drift net during the duration of the set; a reading was taken at the beginning of the set and one at the end. The total volume of water filtered by each net during a set was computed as the basis for estimating the density of drifting fishes. An average CPE was computed for each species using the CPE's from each drift sample, including zeros, where the species was not captured in a given sample. CPE was computed as the number of fish in 1000 cubic feet of water by using the following formula (Valdez et at 1985):