1962 



I f 



I 234 I 23451 2341 234 

 APRIL MAY JUNE JULY 



-f^ — I — I — I — I — I — 1 — I — I — I — I — I — I — I 

 [2 I234I2345I234I234 



APRIL MAY JUNE JULY 



WEEKS 

 FiGUKE 4. — Timing of migration of native juvenile fall 

 ehinooli; salmon (age-group 0) from the Snake River to 

 Brownlee Reservoir by weekly periods, 1962-63. 



The size of native juvenile fall chinook salmon 

 increased throughout the migration period (table 

 2). Early migrants in 1962 averaged 52 mm.; by 

 the final week, average length had increased to 71 

 mm. The migrants averaged larger in 1963 — 73 

 mm. at the start and 81 mm. at the end of the 

 migration period. 



Spring Chinook Salmon 



Spring chinook salmon enter Brownlee Reser- 

 voir from Weiser River and Eagle Creek; their 

 season of spawning is similar, but the sizes and 

 seasons of migration of the juveniles into the reser- 

 voir are substantially ditl'erent. 



Weisei' River pojmlafion. — Juvenile spring chi- 

 nook salmon from the Weiser River first appeared 

 at the Snake River trap in early April and peaked 

 in late April or early May (fig. 5). The migration 

 was nearly complete ])y late May in all years. Daily 

 catches of spring chinook salmon were greatest 

 between 7 and 11 a.m. and .'5 and 7 p.m. except 

 during the peak when diurnal liighs were not 



1234! 234 123451 234 

 MARCH APRIL MAY JUNE 



WEEKS 

 Figure 5. — Timing of migration of juvenile spring chinook 

 salmon from the Weiser River to Brownlee Reser\-oir 

 by weekly i>eriocl.s, 1962-65. 



clearly defined. Daily catches were lowest between 

 10 p.m. and 4 a.m. 



The size of spring chinook salmon from the 

 Weiser River differed from that of wild fall chi- 

 nook salmon from the Snake River in 1962-63; 

 spring fish were age-group I and distinctly larger 

 than fall fish, which were age-group O. In 1964 

 and 1965, however, the difference between these 

 wild spring chinook salmon and the hatchery- 

 reared fall chinook salmon was less apparent by 

 late April when the length ranges merged. In 



.JUVENILE SALMON AND TROUT MIGRATION INTO BROWNLEE RESERVOIR 



207 



417-060 O - 71  



