Rocky Reach site Ij or Z days later. 

 Therefore, the arrival times of the 

 blueback and chinook runs at Rock 

 Island Dam have been used as the ap- 

 proximate times the runs would be ex- 

 pected at Rocky Reach Deun site. 



The rates of travel of individual 

 steelhead were found to vary widely in 

 the Columbia River between Bonneville 

 and McNary Dams. Schoning, Johnson, 

 and Merrell, in an unpublished report, 

 found that these rates varied from 1.9 

 to 14.6 miles per day.' Thus steelhead 

 could be expected to pass Rocky Reach 

 from Z to IZ days after passing Rock 

 Island Dam. 



Chinook salmon . --The season of 

 passage and the number of chinook 

 salmon passing Rock Island Dam are 

 given in figure Z. Chinook runs in the 

 Columbia River are composed of 

 spring, summer, and fall segments ac- 

 cording to the time they enter the river. 

 Each season, the chinook salmon escap- 

 ing the fishery appear during the same 

 time period at Rock Island Dam; spring 

 chinook pass in May and June, summer 

 chinook pass in July and August, and 

 fall chinook make their appearance 

 after August. The spring and summer 

 chinook runs are fairly well defined by 

 their period of passage at Rock Island 

 Dam. The fall run, however, is not 

 clearly marked and appears as a minor 

 part of the escapement late in the 

 season. Fish and Hanavan (1948) re- 

 ported on the bimodality of the chinook 

 runs at Rock Island Dam and reported 

 that the spring run apparently termi- 

 nates during early July. They did not 

 report on the existence of a fcill run, 

 but evidence of a fall run atRock Island 

 Deim is presented in a later section of 

 this report. Considerable overlap of the 

 three segments occurs. All three 

 groups should be expected at Rocky 

 Reach Dam site during the same time 

 period as at Rock Island Dam. 



Spawning ground counts above and 

 below Rocky Reach Dajn site and counts 



^Schoning,. Robert W., Donald R.Johnson, and Theodore 

 R. Merrell. 1950. The expected appearance of certain runs 

 of Columbia River salmon at McNary Dam. Fish Commis- 

 sion of Oregon. February, unpublished report., IS pp. 

 Portland. 



of spring and summer chinook at Rock 

 Island Dam are given in table 1. We 

 found that 77 percent of the spring 

 chinook counted in 1956 and 65 percent 

 in 1957 were in areas above Rocky 

 Reach. In 1957 this meant that about 65 

 percent of the spring run counted over 

 Rock Island, or approximately 11,000 

 fish, were estimated as having passed 

 Rocky Reach Dam site. Twenty-one 

 percent in 1956 and 19 percent in 1957 

 of the summer chinook were counted 

 in areas above Rocky Reach Dam site. 

 Thus, in 1957 the population of summer 

 chinook passing Rocky Reach was es- 

 timated at 6,000 fish. Counts of spring 

 and summer chinook runs passing Rock 

 Island DaJTi in 1956 were not reliable 

 because of the overlap of the runs that 

 season. The reason for this overlap is 

 discussed in a following section. 



Fall chinook salmon spawn in the 

 Columbia River in the limited area be- 

 tween Rock Island Dami and Rocky Reach 

 Dam site, and on extensive spawning 

 riffles above Rocky Reach. Determina- 

 tion of their abundance in this stretch 

 of the main Colunibia River was as- 

 signed to another fishery agency. 



Blueback s almon .--Bluebac k 

 salmon, first appearing at Rock Island 

 Dam in early July, show a peak of 

 abundance around July 15 to Z5. (see 

 figure 3.) To determine the size of the 

 blueback escapement passing Rocky 

 Reach Dam site we have used the sea- 

 sonal counts of blueback at Tumwater 

 Dam (fig. 1) as the number of blueback 

 entering the Wenatchee River system. 

 The remaining part of the run, or Rock 

 Island Dam counts minus the Tumwater 

 Dam counts, has been used as the es- 

 timated number passing Rocky Reach 

 Dam site. This procedure was in pref- 

 erence to usirig stream surveys for 

 obtaining ratios of blueback salmon in 

 the two areas. In recent years the 

 Okanogan run has been the larger of 

 the two runs. Counts of the Wenatchee 

 River run at Tumwater Dam for 1954- 

 57 have ranged from 28 to40 percentof 

 the total escapement counted at Rock 

 Island Dam. The remaining 60 to 72 

 percent of the blueback runs for these 

 years has been attributed to the 

 Okanogan run. The estimate of the blue- 

 back run passing Rocky Reach Dam site 



