appeared in spring chinook spawning 

 areas. These were spring chinook and 

 not summer chinook as evidenced 

 by their characteristic small size, 

 greenish-gray appearance, and early 

 spawning. Summer chinook average 

 larger, take on a reddish color in spawn- 

 ing streams, and spawn later in the 

 season. Apparently a delay along the 

 migration route was responsible for 

 the unusually late passage of mainy 

 spring chinook at Rock Island Daan, 

 Davidson' noted that the upstream 

 salmon migrationin the ColxunbiaRiver 

 is retarded by floods, and at stages of 

 extreme high water may be inhibited. 

 In 1956 a minor flood occurred in the 

 Coliunbia River and the unusually late 

 passage of many spring chinook could 

 be attributed to this occurrence. It 

 should be noted that none of the fish 

 tsigged prior to July 9 was recovered in 

 summer chinook spawning areas that 

 season. 



Another tagging experiment con- 

 ducted during 1956 confirmed our be- 

 lief that fall chinook spawn in the main 

 Columbia River. Sixty- two chinook 

 from the September migration at Rock 

 Island Dam were tagged and released 

 over a 3-day period. No tagged fish 

 were recovered fronn this lot during 

 the streaun surveys made on all tribu- 

 tary streauns. For similar experiments 

 in August, however, in which the num- 

 ber tagged ranged from 24 to 70 chinook, 

 some tags were recovered. Total re- 

 coveries from these summer experi- 

 ments averaged 10 percent. If the fall 

 escapement of chinook salmon spawned 

 in the tributaries, surely some tags 

 would have been recovered; six fish 

 would have been recovered if the 10 

 percent average were obtained. It 

 seems certain that these fish sp>awn 

 only in the main Columbia River, but 

 because of the difficulty of finding 

 tagged fish in so large a river, no re- 

 covery was attempted there. 



Blueback salmon 



Majority of the blueback scdmon 

 passing Rocky Reach Dam site are 



' Davidson, F. A. 1957. The effect of floods on the up- 

 stream migratioii of the salmon in the Columbia River. 

 Riblic Utility District No. 2 of Grant County (Ephrata, 

 Washington). 20 pp. Processed. 



bound for the spawning areas in the 

 Okanogan River in Canada as evi- 

 denced by the strezim surveys (see 

 fig. 7). Very few blueback salmon 

 enter the Entiat, Methow, and Similka- 

 meen Rivers. Blueback seilmon tagged 

 during all parts of the migration period 

 at Rock Island Dam were recovered on 

 the Okanogan River spawning grounds. 

 Spawning commences in the Okanogan 

 River during the lastweek in September 

 and continues throughout the month of 

 October. 



SUMMARY AND CONCLUSIONS 



Investigations of fish runs passing 

 Rocky Reach Dam site have revealed 

 that important runs of chinook and blue- 

 back salmon pass the site bound for 

 S|>awiiing areas in all mciin tributaries 

 between Rocky Reach and Chief Joseph 

 Dam. The runs passing Rock Island 

 Dam would be expected at Rocky Reach 

 Dam site within Ij or Z days since the 

 dams are only Zl miles apart. 



For 1957 the spring and stimmer 

 chinook escapement pass Rocky Reach 

 Dam site was approximately 11,000 

 and 6,000 fish respectively. The es- 

 capement of blueback salmon passing 

 Rocky Reach Dam site was approxi- 

 mately 67,000 fish in 1956 and 43,000 

 fish in 1957. 



Steelhead trout and silver salmon 

 are assumed to pass Rocky Reach; 

 however, their numbers were not deter- 

 mined. Although numerous in the area 

 up to the year 1920, very few silver 

 salmon have been counted at Rock 

 Island Dam since counting commenced 

 in 1933. 



The rate of travel of blueback 

 salmon between Rock Island Dam and 

 Zosel Dam established from tagging 

 experiments was found to be 10.7 days 

 for the 145 miles distance or 13.5 

 miles per day. The difference in time 

 between peaks of abundance at Rock 

 Island and Zosel Dam also indicated 

 that about 10 days were required 

 for fish to travel between the two 

 points. 



14 



