244 BULLETIN OF THE BUREAU OF FISHERIES 



has been selected. (See fig. 61.) It will be noted here that the winter check of the 

 fifth year is represented by only a slight narrowing of the marginal rings and that no 

 new growth of the sixth year is present. 



The scales of one of the fish recovered during 1924 are very unusual. One of 

 them is shown in Figure 58. The nucleus of this scale is the largest in the collection, 

 and the radius of the scale to the second winter check is unusually small. This makes 

 the second year's growth appear extremely slight. The cause of such unusual growth 

 proportions is unknown. It is possible that this fish remained in fresh water for a 

 part of the second year, in which case the nucleus would represent more than the 

 first year. A more typical scale of a fish in its fourth year is shown in Figure 57. 



This experiment is nearly an exact duplicate of experiment No. 7. Both involved 

 the progeny of the spring run of chinooks that spawn in the headwaters of the Willa- 

 mette River. The fingerliugs in both cases were reared at Bonneville and liberated 

 at approximately the same time of the year. The fingerlings preserved in experiment 

 No. 7 are sUghtly larger than those in experiment No. 9, but this difference may 

 well be due to the difference of about six weeks in the dates on which the samples were 

 preserved. The size of the fish at the end of the first year, as shown by the size of 

 the nuclei, was nearly identical. 



The number of returns from these experiments, however, differs widely. The 

 recoveries from experiment No. 7. represent 0.39 per cent of the fingerlings marked, 

 whereas only 0.08 per cent (less than one-fourth as many) were recovered from 

 experiment No. 9. No satisfactory explanation for this difference has been suggested. 

 It could not have been due to a failure of our data to be representative of the actual 

 returns. This may be seen by comparing the returns from the two experiments dur- 

 ing the season of 1925. The 5-year-olds that returned from experiment No. 9 were 

 nearly equaled by the 6-year-olds in experiment No. 7, whereas invariably a much 

 larger proportion of fish from any brood mature during theu" fifth year than during 

 the sixth. These two groups of fish were running simultaneously, and there is no 

 reason to believe that the cannery employees and others who were searching for 

 marked salmon selected one mark in preference to the other. 



EXPERIMENT NO. 10.— BONNEVILLE HATCHERY, AUGUST AND SEPTEMBER, 1922 



Eggs: McKenzie and Santiam Rivers, 1921. 



Reared and marked at: Bonneville hatcliery. 



Mark used: Removal of adipose fin and right ventral fin. 



Number marked: 100,000. 



Liberated: In Tanner Creek during August and September, 1922. 



Age: Approximately 12 months. 



A sample of 25 of the fingerlings preserved on August 28, 1922, averages 76 

 millimeters (3 inches) in length. Their scales have an average of 11.6 rings and an 



33 9 

 average anterior radius of j^ millimeters. The scales of all but two of the finger- 

 lings show an incidental check about 7 rings from the center. The incidental check 

 is followed typically by 3 to 5 rings, which stand out as distinctly heavier and more 

 widely spaced than those preceding the check. (See fig. 62.) The length and scale 

 data are given in Table 23. 



