PROCEDURES 



FISH POPULATION ESTIMATES 



Fish populations were estimated using a mark and recapture 

 method. Population estimates were calculated using Chapman's 

 modification of the Peterson formula (Ricker 1975) . Variance 

 estimates were also made using Chapman's formula. Total length 

 of captured fish was measured to the nearest mm, and weight was 

 measured to the nearest gram. Trout longer than 8.0 in were 

 tagged with individually numbered T-tags in sections downstream 

 from Lincoln. 



We duplicated five electrof ishing sections sampled by Spence 

 (1975) which included: Below Pop's Place, Flesher, Hogum, 

 Poorman-Dalton, and Canyon section (Figure 1) . We remeasured the 

 lengths of sampling sections to account for potential channel 

 changes and errors in identifying previous section boundaries. 

 We also established three new study sections in the Blackfoot 

 River: below the Raymond Bridge, below the Scotty Brown Bridge, 

 and below River Bend FAS (Figure 1) . 



Fish sampling equipment was fitted to the type of water 

 conditions each section presented. In the small stream sections 

 (Below Pop's Place, Flesher, and Hogum) a Coffelt Model BP-IC, 

 gas-powered backpack electrof ishing unit was used. We used the 

 wire hoop positive and a multistrand cable for the negative 

 electrode. We used a Coffelt Model 2C-2000 rectifying unit with 

 a 1500 watt gas-powered generator mounted in an 8 foot long 

 rubber raft in the Poorman-Dalton section. Our positive 

 electrode was a hand-held 1-foot diameter hoop with a braided 

 copper wire negative. On the larger river sections (Canyon, 

 Raymond Bridge, Scotty Brown Bridge, and River Bend FAS) we used 

 an aluminum drift boat mounted with booms; there were four cable 

 droppers per boom. Two rectifying units, a Coffelt Model 2C- 

 2000 and a WP-15, and a 3500 watt generator provided the 

 electrical fields necessary for fish sampling. We also used a 

 Boston whaler with a combination of hand-held and boom mounted 

 electrodes which could be lowered to the stream bottom in an 

 attempt to improve sampling efficiency in the deep pools of the 

 lower river. 



YOUNG-OF-THE-YEAR SAMPLING 



Young of the year (YOY) trout densities were surveyed in the 

 Blackfoot River during early August from the mouth to Aspen Grove 

 Campground near Lincoln. A single habitat type, riffle areas 

 with rock border, was sampled to allow comparisons of YOY 

 densities between sections. This habitat type was chosen 

 because: 1) it provided the most consistent selection of sampling 



