HERRING IN PRINCE WILLIAM SOUND, ALASKA 
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mature fish, or to the unusually high rate of growth causing the larger fish of this 
year class to attain a size suitable for schooling with the older fish at an earlier age. 
That the 1926 year class actually did grow at a faster than normal rate is shown by 
comparing the positions (fig. 8) of mode F in 1928 with mode B in 1924 and mode 
F in 1929 with mode D in 1927. 
The effect of dominant year classes on the catch is expressed in the following 
quotation (Rounsefell, 1930): 
The presence of dominant age groups may have a far-reaching effect; at times a race may be 
exceedingly abundant and at other times exceedingly scarce, for there may be periods of several 
Figure 10.— Age frequencies from Evans Island, southern Knight 
Island, and Montague Island areas for June and July, shown as per- 
centages of each distribution 
years between dominant year classes, the population becoming much reduced before another dom- 
inant year class appears in the catch. The appearance of such a year class may cause excessive 
abundance for a time. When a very dominant year class first enters the commercial catch its 
members will be small, lowering the average size of the fish in the whole catch. Later, as the fish 
of this year class grow older, the average size of the fish in the commercial catch will be gradually 
raised, until another dominant year class appears and temporarily lowers it. 
The fluctuations in the catch caused by these dominant year classes are of great 
importance to the fishery. During the intervals when no abundant year classes of 
