142 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



the year, however, the ratio rose to nearly 10:1; i. e., about 10 fish were caught in 

 the river below the dam for every 1 that reached the dam. Various explanations 

 might be offered, but it seems most likely that, as suggested above, it is due to the 

 fact that a large percentage of the fish entering the river during the late fall spawn 

 in tributaries that enter the main river below the dam. 



We have discussed the importance of the chinook catch above Bonneville during 

 the first few weeks following the closed period, and the fact that the closed period 

 has more effect in spreading the catch out over a longer fishing area than it has in 

 the way of increasing the spawning escapement. Evidently the same effect is apparent 

 in the case of the steelheads. This shift in the relative importance of the fisheries 

 below and above Bonneville is shown somewhat more clearly by the percentages of 



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Figure 8.— Ratio of steelhead trout to chinook salmon in three important elements of the 1938 run, June f>-Ot'tober 28, by weeks. 



the total catch formed by the catches above Bonneville (table 24). For the months 

 of June and July only 4.5 percent of the total catch was token above Bonneville, but 

 during August and September the percentage was 36.2. The relation of this to the 

 net escapement also is shown by the percentages that the catch above Bonneville 

 form of the Bonneville count. For the months of June and July oidy 10.3 percent 

 of the fish counted past Bonneville were later captured hi the fishery above the dam. 

 During the months of August and September, however, 43.9 percent was taken. 



As with the chinooks, the catch of steelheads above Bonneville during the first 

 few weeks following the closed period of August 25 to September 10 exceeds the 

 Bonneville count. This anomaly has been discussed and there seems to be no reason 

 to doubt that the same factors were operating with the steelheads as with the chinooks. 

 It has seemed possible in the case of the steelheads, however, that this phenomenon 



