On some weekends, length measurements and 

 scale samples were taken; on others, the fish 

 were counted and released. After the neces- 

 sary data were recorded, the sampled fish were 

 released in good condition . 



EKiring most of the year it was possible 

 to take length measurements and scale samples 

 from all the bluebacks caught. When large 

 numbers of fish were migrating, a sample usu- 

 ally consisted of all the fish in one of the traps; 

 on occasion it was possible to sample only part 

 of the catch from a single trap. At such times 

 a different trap was picked each day, but no 

 regular rotation was followed. The purpose of 

 this was to avoid bias that might be introduced 

 if size differences existed between the fish 

 caught in different traps. 



The daily samples were pooled into 7- 

 day periods, January 1-7 being the first period, 

 January 8-14 the second, and so on (see table 1). 

 This method simplified comparison of the data 

 between years . Most weekly samples contained 

 at least 2(J percent of the catch, but during some 

 weeKS of heavy migration sample size dropped 

 to as low as 10 percent. 



Scales were taken each day, from 

 representative body lengths, from at least 50 

 percent of the day's sample. Each fish in the 

 scale sample was aged and length -frequency 

 tables by age groups were obtained after the 

 data were pooled into the weekly periods. It 

 was assumed that the fingerling-trap samples 

 accurately depicted the ages and lengths of the 

 total catches. The total catch for each week 

 was computed by direct proportions from 2 -mm. 

 length groups of that week's fingerling-trap 

 sample. Sampling between years was not iden- 

 tical because the proportion of the total catch 

 sampled was not constant; no tests were made, 

 but it is believed that the samples give an ac- 

 curate picture of the trap catches . 



Data on time of migration and number 

 of migrants have been collected since 1946. 

 Age and length data have been recorded since 

 1949. 



A ge Determination 



Scales were used for age determina- 

 tion by counting the number of winter zones 

 (annuli) according to the method perfected for 

 Pacific salmon by Gilbert (1913). The scales 

 were mounted on glass slides in a 4 -percent 

 solution of polyvinyl alcohol, and were always 

 taken, if possible, from the left side below the 

 dorsal fin. All scales were aged unless they 

 were regenerated. 



Fingerling Traps and Their Location 



The Holmes -type inclined-plane finger - 

 ling trapsl', located in the fingerling bypasses 

 of the dam (see fig. 2), were used to collect all 

 samples. The fingerling bypasses provide an 

 escape route for all downstream migrants that 

 enter the auxiliary-water screen pits; however, 

 this number represents only a small fraction of 

 the downstream migrants that pass the dam. A 

 trash sluice that extends across the upstream 

 face of the powerhouse also functions as a 

 fingerling bypass, but it collects only the 

 migrants at the surface of the river . A few 

 migrants pass down the fishways and through 

 the navigation locks. All other downstream 

 migrants pass through the spillway gates or 

 through the turbines. 



The purpose of the auxiliary -water 

 screen pits is to provide additional water to the 

 fishways to attract upstream migrants into the 

 fish ladders. The valve -controlled conduits 

 that carry this water are screened to keep out 

 debris and fingerlings. Figure 3 is a diagram- 

 matic drawing of an auxiliary -water screen pit 

 showing the location of the screens and finger- 

 ling bypasses. 



The fingerling traps are constructed of 

 steel, and can be raised and lowered by hand- 

 operated winches . All water passing through a 

 fingerling bypass is screened by the trap in that 

 bypass. The water is strained through a steel- 

 wire screen that is inclined downward when the 

 trap is operating (fig. 4). A collecting pot 

 j_/Designed by Harlan B.Holmes (Fish and Wild- 

 life Service, 1001 N.E.Lloyd Blvd., Portland, 

 Oregon) and Scott H.Bair (formerly with the Fish 

 and Wildlife Service, and now employed by 

 Chelan County P.U.D. at Wenatchee, Washington) 



