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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 15. — Chinook salmon — comparison of certain estimates as made on the following bases: (1) An 

 average weight of 22 pounds throughout the season; (2) average weights of 15 pounds in May, 20 

 pounds in June, and 25 pounds for the remainder of the year; and (3) average weights for each week as 

 calculated from the trend lines described in the text. The first two were used in the original report by 

 Calkins, Durand, and Rich 



Basis of estimate 



Ratio of catch 

 to escapement 



Percentage 



of Rock Island 



fish in 



total run 



Catch 



attributed 



to Rock Island 



run— in fish 



Catch 



attributed 



to Rock Island 



run — in pounds 



April 17 to May 28 



(1). 



(2). 

 (3). 



95, 300 

 104. 000 

 109, 000 



July 31 to August 27 



(1). 



(2). 

 (3). 



40, 900 



41, 000 

 40, 600 



On the basis of these figures the total catch that may reasonably be attributed to 

 the Rock Island runs is between 500,000 and approximately 600,000 pounds, of which 

 by far the larger proportion was of the valuable spring run. Furthermore, it is of 

 especial importance to note that the Rock Island run forms a particularly large percent- 

 age of the seriously depleted and heavily fished June-July run. 



RATE OF TRAVEL 



These data provide additional information relative to the rate of migration up the 

 river. We have given the reasons for thinking that the interval between the time that 

 the fish appear in Zones 1 and 2 and at Bonneville is approximately 2 weeks. The 

 peak of the run that occurs in late August and early September is obviously an 

 important landmark and should, therefore, provide important evidence on this point — 

 evidence that was not available at the time the original report was prepared. 



From the figures of the numbers of fish caught (estimated on the basis of the 

 trend lines of average weights obtained in 1939) it would seem that the peak of the 

 catch in Zones 1 and 2 came 3 weeks before the peak of the count at Bonneville, instead 

 of 2 weeks (fig. 3). The drop in the catch that occurs between the weeks ending 

 August 20 and 27, however, is due, at least in large part, to the fact that there were 

 only 4 days of fishing in the week ending August 27. The spring fishing season closed 

 on August 25. An estimate may be made of what the catch would have been if the 

 full 6 days of fishing had prevailed, instead of 4 days, by multiplying the estimate 

 already presented by IK- The result is over 71,000 fish; actually a few more than 

 estimated for the week ending August 20. This result indicates strongly that the real 

 peak of abundance in Zones 1 and 2 came not earlier than the week ending August 27 — 

 2 weeks earlier than the actual peak in the Bonneville count and quite in agreement 



