T — I — I — I — I — I — I — I — I — I — 1 — I — 1 — I — I — I — I — I — I — I — I — I — r 



1952 : 144 FISH 



— - 1953 : 89 FISH 



12 2 4 6 8 10 12 2 4 6 8 10 12 

 AM HOUR PM 



Figure 8. --Hourly catches of allver* in 1952 and 1953- Each 

 hour representB th« suamatloa of the y«ar'0 catch 

 for that hour. 



12 2 4 6 8 10 12 2 4 6 8 10 12 



AM ^^ouR PM 



Figure 9> — Hourly catches of steelheads in 

 1952 and 1953- Bach hour re- 

 presents the sunmation of the 

 yeeir's catch for that hour. 



peaks at 7> 9, and 10 a.m. Because compara- 

 tively few fish vere taken, these hours may 

 be of no slgnlflccmce. 



Steelheads 



Well-marked peaks of steelheads 

 occurred at 6 a.m. in 1952 and 1953* hut 

 only 1953 had a noticeable evening peak 

 (fig. 9). Two 72-hour fishing periods in 

 1953 having similar hours of sunrise and 

 sunset were plotted. Both periods have 

 peaks at 8 p.m. , but the morning periods 

 lack any discernible modes (fig. 10). 



Discussion of Hourly Movement 



Hourly fishing of the flngerllng 

 traps in 1^2 and 1953 indicates that at 

 dawn and dusk there is an increatse In the 

 migration rate of most downstream^ilgrant 

 salmonids at Bonneville Dam. Chinook fln- 

 gerlings and yearlings showed dawn and 

 dusk peaks in both years. Steelheads had 

 a morning peak in both years, but an eve- 

 ning peak only in 1953- Silvers and blue- 

 backs exhibited a tendency to migrate at 

 all hours. The data on hourly migration 

 are not conclusive because too few years 

 have been sampled; they are nevertheless 

 indicative of migration behavior. 



12 2 4 6 8 10 12 2 4 6 8 10 12 

 AM PM 



HOUR 



— APRIL 28- MAY I 323 FISH 

 — MAY 4- MAY 7 258 FISH 



Figure 10. --Percent of steelheads caught 

 each hour during two 72-hour 

 periods in 1953- 



