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I I I I I I I I I I I I I I I I I I I 3.0 METHODOLOGY 3.1 BASIC STUDY DESIGN The Lake Powell inflow of the Colorado River was sampled twice in 1994, once in April before spring runoff and again in August when Colorado River flows had returned to base levels. The objectives of pre-runoff sampling were to measure densities of age-O Colorado squawfish prior to spring runoff and to assess levels of predation on age-O squawfish. The purpose of the post-runoff sampling trip was to measure densities of age-O squawfish after runoff and to again assess predation on age-O squawfish. Each sampling trip was 5 days long. A crew of four biologists (1 NPS and 3 BIO/WEST) participated in each trip. Pre-runoff sampling was conducted April 18 - 22, post-runoff sampling August 22 - 25, 1994. 3.2 SAMPLING GEAR Electrofishing, seining, and passive light traps were used to capture fish in the Lake Powell inflow. A brief description of each gear and its associated data code are presented in Table 1. For each gear type fish were counted and released. All native species were measured (total length) and weighed (in grams). Adult Colorado squawfish (>200 mm TL) were PIT-tagged if not previously tagged. Table 1. Description of fish sampling gear used in the Lake Powell inJJow Study, 1994. GEAR DESCRIPTION CODE Electrofishing 220-voH DC with Coffelt VVP-15 on 16' aluminum Jon boat EL Seine SB SE 15' x 4' with 1/8- delta mesh 10' x 4' with 1/16- delta mesh Ught Trap Floating clear plastic trap with integral light source (quatrefoil design) LT 3.2.1 EIectrofishine Electrofishing was used to capture adult and juvenile fish along sborelines and return channels. All fisb were captured using a Coffelt VVP-15 pulsed DC elearofisbing unit, with a duty cycle of 20% and a pulse rate of 40 Hz. Normal operating level was 190-220 volts and 8-10 amps. This system was operated from a 16 it aluminum Jon boat and powered by a 5500 watt Yamaba generator. Anodes of three-pronged 1/4-inch stainless steel braided cable were used. Catcb rates for elecuofisbing were calculated by pooling the data. This method is simply the total number of fisb divided by total time sampled. CPE's are expressed as number of fish per 10 bours of elecuofisbing. 3.2.2 SeIDiD!! Small mesh seines were used in backwaters, shorelines and return channels to capture age~ and juvenile fish. The area seined was measured and the catch per effort (CPE) was computed as number of fish per 100 square meters of area sampled (number fisbl1OOml. Water deptb, temperature and substrate type were recorded for each seine hauL 3