SALMON RUNS OF THE COLUMBIA RIVER IN 1938 



117 



river above Bonneville, this will tend to magnify the importance of the spawning in 

 the river above Bonneville, including that above Rock Island. Undoubtedly a part 

 of the commercial catch of all species except the blueback is composed of fish derived 

 from the tributaries below Bonneville, but it seems probable that this forms a relatively 

 small part of the total catch of chinook salmon, at least until after the peak of the fall 

 run. There is a very large count of chinooks at Bonneville immediately after the 

 beginning of the closed period in August — certain evidence that a large proportion 

 of the fish that are in the river at that time 

 are derived from populations spawning 

 in the higher tributaries. On the whole we 

 feel fairly confident that only a relatively 

 small part of the commercial catch of this 

 important species that is made before the 

 first of October comes from the runs into 

 tributaries below Bonneville. 



An understanding of the analysis of 

 these runs, particularly in relation to the 

 fish destined to spawn in the upper Colum- 

 bia River above Rock Island Dam, may 

 be aided by the following discussion (see 

 also fig. 2). 8 While this particular treat- 

 ment is related specifically to the run to 

 Rock Island, a similar treatment could be 

 applied to any other tributary runs for 

 which similar data were available. 



Let us assume: 



A. That the estimated escapement at 

 Celilo is the total escapement for the total 

 run of the period; and 



B. That the ratio between the escape- 

 ment at Rock Island Dam and the catch 

 made from the same stocks of fish 

 that furnished this escapement is the 

 same as that between the escapement 

 at Celilo and the total catch. This 

 assumes that there is no appreciable 

 loss between Celilo and Rock Island, 

 and that, for each species, the proportion 

 of Rock Island fish caught is the same as the average for all salmon of the species 

 that are passing through the fishery at the same time. 



From this it would follow also that the relation between the escapement at Rock 

 Island Dam and the run referable to this escapement will be the same as that between 

 the escapement at Celilo and the total run. 



Having then determined, for a selected time interval, the total catch, denoted 

 by C, the escapement at Celilo, denoted by Ei, and the count at Rock Island, denoted 

 by E 2 , we are able to determine the following: 



• This clarifying symbolic treatment was contributed to the original report of the Board ot Consultants by Dr. Durand, who 

 has kindly permitted slightly altered repetition here. 



449G68— 42 3 



Figure 2.— Diagram of the ultimate subdivisions of the 

 main run of chinook salmon entering the Columbia River, 

 illustrating the various ratios. R denotes total run; C, 

 denotes total catch below Bonneville Dam; BC denotes 

 Bonneville count; Ci denotes catch above Bonnevilt 

 Dam; Ei denotes escapement at upper limit of commercial 

 fishing; Ei denotes escapement at Rock Island Dam; " 

 denotes diversions of unknown amounts at various points 

 In the river. 



