298 
BULLETIN OF THE BUREAU OF FISHERIES 
age histograms show that this shifting in the length mode was due to the growth of 
the dominant 1920 year class, which was 6 years old in 1926 and 7 in 1927. 
The age frequencies presented in Table 32 show that in no case is there a sym- 
metrical distribution of ages around a mode, such as one would expect to find in a 
population in which the annual increments of new members were about equal. In 
fact, very unequal proportions of different age groups seems to be the rule. There- 
fore, it is safe to conclude that our data demonstrates conclusively that dominant 
year classes are ordinarily present in the Alaska herring. 
Table 32. — Frequency at each age 
Age 
(years) 
San Diego, 
December, 
1926 
Stephens 
Passage, 
January, 
1928 
Larch Bay, 
August, 
1927 
Halibut 
Cove, gill 
netted, 
April, 1926 
Halibut 
Cove, beach 
seined, 
April, 1926 
Dogfish 
Bay, Au- 
gust, 1925 
Lower 
Kachemak 
Bay, Au- 
gust, 1926 
Shuyak 
Strait, 
July, 1925 
9.. 
10 . 
11 . 
12 . 
13. 
14. 
15. 
16. 
17. 
Total . 
Num- 
ber 
46 
Per 
cent 
Num- 
ber 
8.7 
76.1 
13.0 
9 
22 
9 
109 
4 
3 
6 
13 
4 
2 
2 
1 
184 
Per 
cent 
Num- 
ber 
4.9 
11.9 
4.9 
59.2 
2.2 
1.6 
3.2 
7.0 
2.2 
1. 1 
1. 1 
. 5 
Per 
cent 
19.0 
31.8 
23.8 
12.7 
7.9 
3.1 
1.6 
Num- 
ber 
89 
Per 
cent 
2.2 
1. 1 
318 
37. 1 
4.5 
12.lt 
6.7 
1.1 
Num- 
ber 
24 
66 
64 
79 
31 
10 
22 
22 
4 
340 
Per 
cent 
7.1 
19. 
18.8 
23.2 
9. 1 
2.9 
6.5 
6.5 
1.2 
2.4 
2.4 
.6 
Num- 
ber 
85 
Per 
cent 
1.2 
1.2 
3.5 
3.5 
9.4 
50.6 
25.9 
4.7 
Num- 
ber 
Per 
cent 
Num- 
ber 
2.0 
1 . 2 
2.0 
5.7 
12.2 
3.7 
22.lt 
23.7 
4.9 
5.7 
13.5 
2.0 
.4 
149 
Per 
cent 
0.7 
1.3 
2.7 
18.8 
12.1 
4.7 
42. S 
13. 4 
2.7 
.7 
.7 
Age 
(years) 
Shvak Strait, 
July, 1926 
Elrington Pas- 
sage, July and 
August, 1925 
Elrington Pas- 
sage, June and 
July, 1926 
Elrington Pas- 
sage, June and 
July, 1927 
Eshamy Bay, 
September, 1926 
McClure Bay, 
September, 1927 
Dutch Harbor, 
August, 1928 
1 
Number 
Per cent 
Number 
Per cent 
Number 
Percent 
Number 
Per cent 
Number 
Per cent 
Number 
Percent 
Number 
Per cent 
2 
21 
4.9 
1 
0. 6 
3 
13 
7.9 
35 
9.0 
13 
3.0 
4 
2.2 
1 
.6 
1 
1.2 
4 
1 
1.3 
42 
25.5 
137 
35. 4 
21.2 
207 
48.4 
12. 1 
17 
9. 5 
30 
17. 6 
6 
7.9 
59 
35.8 
82 
52 
27 
15. 2 
31 
18. 2 
6 
10 
13.2 
11 
6.7 
120 
31.0 
38 
8.9 
114 
64.1 
3.4 
23 
13. 5 
58 
68.2 
2 
2.6 
11 
6.7 
3 
.8 
78 
18.2 
6 
68 
40.0 
10 
18.8 
8 
18 
21.0 
6 
3.6 
3 
.8 
2 
. 5 
1 
. 6 
1 
. 6 
4 
4.7 
9 
16 
21.0 
4 
2.4 
1 
.3 
9 
2. 1 
1 
. 6 
7 
4. 1 
10 
3 
3.9 
9 
5.5 
1 
.3 
4 
1.0 
2 
1. 1 
6 
3. 5 
4 
4.7 
11 
6 
7.9 
10 
6. 1 
3 
.8 
3 
.7 
1 
. 6 
1 
.6 
12 
13 
17.1 
2 
. 5 
1 
.2 
5 
2.8 
2 
2.4 
13 
1 
1.3 
1 
. 6 
14 
2 
2. 6 
76 
165 
387 
428 
178 
170 
85 
OCCURRENCE OF DOMINANT YEAR CLASSES 
Whether the conditions that cause certain year classes to survive in unusual 
numbers are entirely fortuitous or whether these conditions recur in cycles, is a 
question. Linked with this comes the question as to the effect the spawning of a 
dominant year class will have on the stock of the following years. Gilbert and Rich 
(1927) found that in the Karluk River the red or sockeye salmon ( Oncorhynchus 
nerka) presents 5-year cycles. Quoting: 
The graph shows clearly the cyclic character of the runs of red salmon in the Karluk River. 
Since the Karluk salmon are predominantly 5-year fish, we anticipate a correlation between the 
run of any year and that of the fifth year preceding, the fifth year following, etc. * * * If it 
