GROWTH AND MATURITY OF SALMON IN THE OCEAN 
41 
Table 8. — Percentage of mature and immature females taken outside the river at different times during 
the season 
Date 
May 8 to 10, 
May 24 
June 4 
June 10 
June 21 
June 25 
Percentage due to mature 
during — 
Year 
taken 
(mature) 
16. 9 
0. 3 
1. 5 
11. 1 
01. 3 
42. 9 
Next 
year 
71. 7 
71.9 
55.9 
5.5. 5 
29. 1 
57, 1 
Second 
year 
11.3 
21. 8 
42. n 
33. 3 
9. 6 
Total 
percent- 
age of 
imma- 
ture fish 
83. 1 
93. 7 
98. 5 
88. 9 
38. 7 
57. 1 
Date 
July 2 
July 28 
Aug. 13 
Aug. 13 to 17._. 
Sept. 18 and 19 
Percentage due to mature 
during — 
Year 
taken 
(mature) 
48. 5 
80. 4 
88. 2 
Next 
year 
37. 6 
19. 6 
12. 7 
10. 9 
Second 
year 
13. 9 
4. 9 
Total 
percent- 
age of 
imma- 
ture fish 
51. 5 
24. 4 
13.fi 
11. 7 
91.7 
Reference to these tables shows that, with the exception again of the three 
collections made in the lower part of the Columbia estuary, the fish found inside 
the river are all mature. This is so obviously in accord with the familiar facts 
of the life history of the chinook salmon that it would be quite unnecessary to 
present the data given in Table 7 were it not for the unusual presence of immature 
fish in those collections made in the estuary and the desirability of presenting a 
table that may be compared with the similar table for the fish taken in the ocean. 
In the case of the fish taken outside the river, it is apparent that during May and 
the first half of June the percentage of immature fish is high. This percentage 
gradually falls during the latter part of June, July, and August, until by the middle 
of August only about 10 per cent of the fish taken outside are immature. The 
one collection made in September shows a high percentage of immature fish again. 
The number of fish included in this September collection is too small to be reliable 
(12), but it would not be surprising to find that at this time of year most of the 
fish taken outside are immature, since the height of the run of chinooks in the 
Columbia comes during August, and the result of the entrance into the river of 
most of the maturing fish would be to leave mainly iramature fish outside. At 
the time these collections were made there was little outside fishing done during 
the fall months, so that it was impractical to gather adequate data. 
The percentages of mature fish taken outside are shown in Figure 11. It is 
evident that, with the exception of the last record (that made in September), 
there is a fairly steady increase in the percentage of mature fish in the collections. 
The trend of this increase has been calculated, omitting the record for September 
and that for May 18, 1920, which has previously been shown to be unreliable for 
this purpose, and assuming that a straight line will approximate the most probable 
change in the percentage of mature fish taken. The trend has been calculated 
by the method of averages, ^ weighting the various points by the number of indi- 
viduals contained in the collections that established the points. The trend, shown 
on the graph by the broken line, fits the later part of the data remarkably well, 
but it fails to fit accurately the data for the early part of the season. It is probable, 
however, that this trend represents the true tendency as accurately as could be 
done by any such generalization of the observed data. It is quite conclusively 
» For a description of this method see Lipka, Graphical and Mechanical Computation, Wiley, 1918. 
