PACIFIC HERRING 
297 
frequencies) of each of the four yearly curves and dividing by four to get the arith- 
metic mean for each ordinate. (Fig. 36, top curve.) With this average curve as 
a base, the deviations of each of the four years from the average curve were plotted 
so that frequency greater than the average ap- 
pears above the line (as solid black), less than 
the average below the line. 
Figure 36 shows more clearly than Figure 35 
the progression of sizes through the commercial 
catch from small fish (roughly 16 to 19 centi- 
meters) in 1924 to large fish (roughly 22.5 to 
25.5 centimeters) in 1927. It shows even more 
clearly the progression of a poorly represented 
size group, which, commencing at 15-17 centi- 
meters in 1925, moves to 17-20 centimeters in 
1926, and to 18.5-21.5 centimeters in 1927. The 
group between 17 and 21 centimeters in 1927 
appears from the size distributions of Figure 35 
to be of great importance, but Figure 36 shows 
it to be below the averages for those sizes, while 
the group from 11 to 15 centimeters in 1927 ap- 
pearing from the size frequencies to be unim- 
portant is shown by Figure 36 to deviate almost 
in its entirety above the average frequency for 
the four years. 
The view that the progression of sizes in 
Elrington Passage is due to the growth of fish of 
dominant age groups is sustained by age analy- 
ses. (Fig. 37, Table 32.) The age histogram 
for 1925 represents only a small portion of the 
fish in the length distribution, but those for 1926 
and 1927 are quite representative. The shift of 
the 1919 and 1920 year classes from 4 and 5 years 
of age in 1925 to 6 and 7 years of age in 1927 is 
very apparent. While there is undoubtedly a 
small percentage of error in the age readings yet 
they are of great value in interpreting the signif- 
icance of the size modes, and the consistency of 
the results obtained by the two methods is fur- 
ther evidence of their validity. 
Eshamy Bay and McClure Bay, about 
10 miles apart, show no racial differences, so 
their length and age distributions have been 
compared for 1926 and 1927. (Figs. 38 and 
39.) Both of the length frequencies present very distinct and sharply defined 
modes, the 1926 Eshamy Bay mode being at 23 centimeters and the 1927 
McClure Bay mode at 24 centimeters, a forward progression of 1 centimeter. The 
/O /4 18 22 26 30 
LENGTH IN CENTIMETERS 
Figure 36. — Deviations of the length frequency 
distributions of each year from 1924 to 1927 from 
the average of the four years for summer herring 
of Elrington Passage and immediate vicinity 
