MIGRATIONS OF COD 
113 
The number of fish included in the III, IV, and V year classes in this table appear 
to be sufficient to give a good idea of the frequency distribution of lengths at the 
completion of the first growth zone for this particular sample of fish. Thus the III 
and the IV year olds present simple modes at 7 inches, while the V-year fish have two 
modes, at 6 and at 10 inches, respectively. This does not necessarily imply that the 
V-year fish during their first year of life were divided into slow-growing and fast- 
growing groups. What is more probable, the fish may have originated from dif- 
ferent spawning periods, for the 6-inch fish might have come from eggs deposited 
late in winter, while the 10-inch fish could have hatched early in the winter. If this 
were so the difference in the calculated first-year size (between 6 and 10 inches) 
could be due largely to a difference in age and not to rate of growth. 
The role of the circulus count in defining the first full year of growth already has 
been discussed. 
In order to show the relation between the calculated lengths at the end of the first 
year and the number of circuli formed in the first growth zone, most of the III, IV, 
and V year scales included in the preceding table have been arranged in Table 43 
according to number of first-zone circuli. 
Table 43. — Relation between number of first-zone circuli and calculated length at the formation of the 
first annulus 
Circuli in first zone 
Average 
length, in 
inches, 
calculated 
from first 
growth 
zone 
Fish 
Circuli in first zone 
Average 
length, in 
inches, 
calculated 
from first 
growth 
zone 
Fish 
Circuli in first zone 
Average 
length, in 
inches, 
calculated 
from first 
growth 
zone 
Fish 
8-9 
3. 3 
1 
16-17 
6. 0 
56 
24-25 
7.8 
58 
10-11_ 
5. 1 
1 
18-19 
6. 2 
94 
26-27 
9.2 
19 
12-13. 
4. 3 
4 
20-21... 
7.0 
123 
28-29 
10.0 
5 
14-15 
5.5 
39 
22-23 
7.4 
103 
It is significant that the calculated lengths of fish with 20 to 21 circuli in the 
first-growth zone of their scales averaged 7 inches, for this agrees with the 7 to 8 
inches estimated as the average size at 1 year attained by southern New England cod, 
based on collections of juveniles. In Table 44, which follows, therefore, the extremes 
in the calculated sizes for each age group are due partly to a difference in age, as 
measured by months. This is particularly evident in the I-year class, which may 
include individuals as young as about 8 months and as old as about 15 months, but 
would not be so evident with the higher age classes, for the first year’s discrepancy, 
not being cumulative, would tend to be of less and less importance in comparison 
with the actual differences in the rates of growth which do exist. 
