SALMON RUNS OF THE COLUMBIA RIVER IN 1938 137 



For the bluebacks this comprises practically the entire season. But there is evidence 

 that the. catch during the central portion of the season constitutes a higher percentage 

 of the run than at the beginning and end of the run — in other words that the fishing 

 is more intense while the fish are most abundant. For the period covered by the 

 weeks ending June 11 to July 16 the estimated number of fish caught is 139,000, 

 while the escapement is 37,600; giving a ratio of catch to escapement of 3.69:1. Ap- 

 plying this ratio to the Rock Island count for the period gives an estimate of 60,500 

 fish weighing 181,500 pounds that may be attributed to the Rock Island runs during 

 this period only. 



The percentage that the Rock Island count constitutes of the total estimated 

 escapement of this species is a measure of the relative importance of the Rock Island 

 runs in the total. On the basis of the entire season the percentage is 40.58, and on 

 the basis of the central, more important period of weeks, the percentage is 43.55. 

 From these figures it appears that approximately four-tenths of the entire run of 

 bluebacks on the Columbia River in 1938 was composed of fish derived from the 

 runs to the upper Columbia River, and that the aggregate commercial catch was 

 approximately 182,000 pounds. 



The application of the second method for converting poundage figures into 

 numbers of fish increases the estimate of the number of fish taken above Bonneville, 

 and correspondingly decreases the estimated number in the escapement — since this 

 is derived by subtracting the estimated catch above Bonneville from the Bonneville 

 count. As shown in table 21, it gives an estimate of 39,400 bluebacks taken above 

 Bonneville, instead of 32,800, on the assumption of an average weight of 3 pounds. 

 The estimated escapement is reduced to 35,600 from 42,200; the ratio of catch to 

 escapement is 4.11:1, and the percentage of the total escapement later counted at 

 Rock Island is 48.05. The total catch and poundage attributable to the Rock Island 

 runs can be determined by multiplying separately the catches made above and below 

 Bonneville by the percentage of Rock Island fish in the whole run (48.05 percent). 

 For the number of 3-pound fish caught below Bonneville this gives 51,500, and for 

 the number of 2K-pound fish caught above Bonneville 18,900 — a total of 70,400 fish 

 with an aggregate weight of 202,000 pounds. A similar estimate for the period from 

 June 5 to July 16 gives a ratio of catch to escapement of 4.66:1, and the percentage 

 of Rock Island fish in the total run is 52.57. The total catch on the basis of these 

 ratios is 76,500 fish of an aggregate weight of 219,300 pounds. 



These estimates show quite conclusively that in 1938 about half of the blueback 

 run was derived from the tributaries above Rock Island; that about four fish were 

 caught in the commercial fishery for every one that was left to propagate, and that 

 the total weight of the fish taken in the commercial fishery and derived from the Rock 

 Island runs was of the order of 200,000 pounds. 



