8006 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I I I sexual characteristics such as spawning coloration or breeding tubercles. Spawning was confirmed and time of spawning was estimated based on when larvae were collected. Population Estimate for the Upper Site As part of standard sampling of the upper site during base-flow, large-bodied fish were collected at one site using a four-pass, removal, sampling design. This was done to obtain abundance estimates for each species and to test if removal sampling in a river of this size was practical at base flow. The sample site was a pool, 130-m long that averaged 23-m wide (width ranged 9-26 m) and was similar to other baseflow refugia pools in the upper reach. Within the thalweg, which was about 5-m wide, average depth was 0.8 m and maximum depth was 1.2 m. Outside the thalweg, along the margins of the pool, depths were < 0.5 m due to sand deposition. Substrate in the reach was predominately gravel, but the pool also contained sand and boulders. To meet the assumption of closure required by the population estimator, fish were confined in the reach with nets (White et al. 1 982). An upstream riffle was blocked by a 10-mm mesh net and a shallow, downstream, low-velocity run was blocked with a trammel net partially covered by a 10-mm mesh net. Fish were collected for the population estimate by bank electrofishing. A 5000-watt generator provided electricity to a Coffelt@ VVP-1 5 set to 300 volts, 2.5-4 amps, 30 pulses/second, and 40% pulse width. Three netters stood 1-m abreast and electrofished in an upstream direction. Fish were collected and held in a live-car during each pass. Fish removed from the trammel net were counted and included with fish caught by electrofishing on each pass. All fish were released alive after the fourth and final pass. Population size of each species within the pool was estimated with the computer program CAPTURE (White et al. 1982). 9