The average depth of water in the pools of the ladder was calcu- 

 lated to be $o5 feet for the h pools in 19h9 and U.U feet for the 3 

 pools as operated during 19.^1 « 



THE EXPERIMENT 



V/ith the completion of the Denil-type ladder at Dryden Dam 

 in the spring of 19l;95 plans were formulated for fish-passage obser- 

 vations at both the Denil-type and pool-type ladders, in connection 

 with the migration of blueback salmon ( Oncorhynchus nerka) and chinook 

 salmon ( Oncorhynchus tshawytscha) on their way to their spawning grounds. 



The method used for making comparative counts of fish utilizing the 

 individual ladders was for the observer to alternate his attention from 

 one ladder to the other for approximately equal periods. When two observers 

 were available, fish were counted simultaneously in both ladders. 



During the 19li9 migration, llU hours 20 minutes of observa'' ions were 

 made, with a total of 260 fish being counted through the ladders. However, 

 not as many fish were tallied as had been anticipated, since, as the result 

 of flow conditions over this relatively low dam, a great many were able to 

 negotiate the dam without using the ladders. Fish other than salmon seen 

 ascending the Dryden ladders were rainbow or steehead trout ( Salmo 

 gairdenrii) , Dolly Varden trout ( Salvelinus malma ) , suckers ( Catostomus 

 so. ) and Squawfish ( Ptychocheilus oregonensis ) . 



In I9L9, a total of 259 fish was counted through the Denil-type ladder 

 in 6U hours and $ minutes, while only one fish was observed passing 

 through the pool-type ladder in 50 hours l5 minutes of observation. Data 

 concerning these observations are listed in Table 1. The observations 

 were extended to the 19^0 season, but were soon abandoned after no fish 

 were seen using the ladders over a period of several days. High water 

 conditions resulted in the fish finding other means of negotiating the 

 dam than by the ladders. 



From the standpoint of the experimental observationo, water levels 

 during the 19^1 season were more satisfactory and salmon used the fish 

 ladders to a greater extent. Both the Denil-type and pool-type ladders 

 were observed for a total of U6 hours IiO minutes during which time l^SS^ 

 fish ascended the Denil-type ladder and 225 fish were counted through the 

 pool-type ladder. The data on 195l observations can be found in Table 2. 

 Thus in the total time that counting was conducted in 19^9 and 19^1 (207 

 hours ho minutes, 89 percent of the fish used the Denil-type ladder and 

 11 percent used the pool-type ladder. As will be noted from Tables 1 and 

 2, a larger percentage of fish negotiated the dam in 195l by use of the 

 pool-type than in I9U9. 



10 



