GBOWTH AND AGE AT MATURITY OF THE PACIFIC RAZOB CLAM 
229 
this age (1.54 centimeters in three months) this difference amounts to one month's 
growth. 
It must be remembered, in comparing these lengths with possible size limits, 
that at the above lengths but 50 per cent are mature. A recommended size limit is 
intended to provide opportunity for all individuals to spawn at least once. 
RELATION OF AGE AND LENGTH TO MATURITY 
The comparison of the results of the last two sections throws an interesting 
light on the process of maturing on the various beds of the Pacific coast. From a 
study of Table 8 and Figure 19 we see that there is a Avide difference in age at ma- 
turity, but there is a close agreement in size. While the differences in size are small 
in comparison with those of age, an examination of the data shows them to be ord- 
erly and significant. Clams from beds where growth is slow, while older at ma- 
turity, are also smaller. The Washington clams, which show the most rapid 
growth, are the youngest but are largest at maturity ; conversely, those at Cordova 
which show the slowest growth are the oldest but the smallest. 
QUANTITATIVE MEASURES 
A quantitative measure of the respective influences of age and length may be 
obtained by analysis of the figures given in Table 8. Between the youngest and 
the oldest there is a difference of 2.2 years, or, compared with the average of the 
three ages (3.1 j^ears), a variation of 71 per cent. In contrast with this we have a 
variation of 0.55 centimeter in length, which, compared with the average length 
(10 centimeters), gives but 5.5 per cent. Therefore, in the process of maturing 
an increase in size of 1 per cent accompanies the same sexual development as an in- 
crease in age of 13 per cent. 
Table 8. — Age and length at maturity 
Locality 
Maturity 
Age 
Length 
Washington 
2.0 
3.2 
4.2 
10. 30 
9. 91 
9. 75 
Swiclishak 
Cordova 
The data of Table 8, plotted in Figure 19 as line W-S-C^ show the influence 
of both age and length on maturity. If age alone determined maturity, this line 
would be perpendicular and clams from all beds, while varying in size, would 
mature at one average age. If size alone determined maturity, the line would be 
horizontal. The age would vary, but the size would remain constant. From this 
line another ratio may be obtained by comparing the average relation of age to 
length and this same relation in respect to maturity. For example, from Figure 
14 (p. 218), on the Swickshak curve near the size of maturity (3 to 4 years of age), 
one year's growth is equal to 2.89 centimeters, or, using this proportion, 0.346 of 
