GROWTH AND AGE AT MATURITY OF THE PACIFIC RAZOR CLAM 
223 
However, more definite data may show a closer correlation between the rate of 
growth and the length of growing season of the different beds, which in turn may 
be confined to clams below a certain size. The maximum for the Washington 
clams is about 12 years, while those from Alaska may reach an age of 17 or 18 
years, but the large number of specimens necessary for an average to extend the 
growth curves to those ages are not available. 
The ordinarj^ growth curves, samples of which have been presented in Figure 
14, are constructed from a table in which the average (median used) length of 
each age is calculated. With the same data used to calcidate the values for the 
Swickshak growth curve the process was reversed, and the aAcrage age of each 
length class was determined (fig. 15 and Table 5) and a growth curve constructed 
from these figures (Weymouth, McMillin, and Rich. 1925). As the annual interval 
is very much larger than is convenient to use, tlie points at the lower end of the 
curve are irregular. The range was too small to calculate the tenth and ninetieth 
percentiles until the fifth year. Up to the age of five years the two curves might 
well be considered as coinciding; then the second "regression" (the average age 
for each length) tends to fall below the first, but later it rises and crosses it at 
about nine j-ears, after which there is a distinct separation of the two curves. 
This shows that the correlation between age and size is less as the clams increase 
in age. In younger specimens size is a fair indication of age. A 2-year-old and 
a 4-year-old clam are greatly different in length, but the difference betAveen a 
9-year-old and an 18-year-old clam m^ay amount to very little, with the possibilit}' 
of the younger being the larger. 
Table 5. — Swickshak beach 
Length on age 
Age on length 
Age in years 
Percentiles 
Length in centimeters 
Percentiles 
10 
50 
90 
10 
50 
90 
1 
0.24 
1.94 
4. 70 
8. 13 
10.30 
11.92 
12. 74 
13. 27 
13. 57 
13.94 
14. 29 
14. 53 
15. 19 
0. 38 
2. 70 
6.41 
9. 28 
11.49 
12. 74 
13. 70 
14. 19 
14. 63 
14.94 
15. 25 
15.61 
16. 12 
15.96 
0.76 
3.52 
7. 81 
10.94 
12. 68 
13.76 
14. 51 
15. 11 
15. 60 
15.93 
16.28 
16. 61 
16. 78 
1.5 
1. 00 
2. 00 
2.00 
2. 00 
2.60 
3. CO 
3.00 
3. 16 
3. 87 
4.05 
4.67 
5.03 
5.94 
7. 12 
8.83 
10.03 
11.25 
2 
2.5 
3..-- 
3.5 
4 __ _ 
4.5 
5 
5.5. _ 
6.._ __ _ 
6.5 _ 
7 _ 
7.5 
8 
8.5 
9 _ 
9.5 : 
10 _ 
10.5. __ 
11 
11.5._ _ 
12 _ 
12.5 
4.09 
4. 85 
5. 77 
6. 91 
8.08 
10.03 
6.04 
7.25 
9. 15 
10.97 
11.94 
12. 78 
13 
13.5.- _ _. 
14 
14.5 _.. 
15. 5 _- 
16.5- 
17. 5 
