AGE AND GROWTH OF THE PACIFIC COCKLE 
639 
Table 2. — Growth constants for different localities 
Locality 
Dis- 
tance, 
miles 
Maxi- 
mum 
age, 
years 1 
Maxi- 
mum 
length, 
centi- 
meters 
IV 
Accel- 
era- 
tion 3 
Locality 
Dis- 
tance, 
miles 
Maxi- 
mum 
age, 
years 1 
Maxi- 
mum 
length, 
centi- 
meters 
IV 
Accel- 
era- 
tion 3 
Tillamook 
Copalis 
Kake 
Cordova _. 
0 
100 
1,000 
1,480 
7.5 
6.8 
12.4 
8.15 
7.00 
9.60 
0. 515 
.515 
.727 
1.235 
-0. 497 
-.986 
-.889 
-1.207 
Constantine Harbor. 
Snug Harbor. 
Kukalc Bay . 
Port Moller 
1,500 
1,800 
1.940 
2, 240 
11.4 
14.8 
15.2 
7. 30 
10.90 
7.40 
1.051 
1.076 
1. 127 
.727 
-1.342 
-.603 
-1.285 
-1.363 
1 Actual ring number; to obtain age substraet approximately one-half year. 
2 .Pi, = relative growth rate= ^ ^ ^ at t = 2. 
at 
3 Acceleration=4£!A 
at 
Scatter diagrams prepared from these data show, in most cases, definite trends 
that agree with the correlations obtained for the razor clam. (Weymouth, McMillin, 
and Rich, 1930; Weymouth and McMillin, 1930.) 
As in the razor clam, geographical position shows the highest correlation with 
maximum age. A lower correlation was obtained between length and age. Cockles 
from the northern beaches reach the greatest ages and largest sizes. The relative 
growth rate at two years shows a high positive correlation with age and with length. 
This agrees with the relation shown by razor-clam growth in which a high relative 
growth rate at two years is associated with great age and large size. The reverse 
correlations must exist between early growth rate, age, and length. Figure 7 clearly 
shows this relation to be true in the growth of the cockle. A high positive correlation 
between age and length is also shown. The cockles reaching the greatest age are 
the largest. 
In the razor clam a confirmation of the relations observed between localities 
was obtained by comparing the growth of the sexes. (Weymouth, McMillin, and 
Rich, 1930.) In the case of Cardium, such a check is impossible, as the cockle is 
hermaphroditic. (Edmondson, 1920.) 
CONCLUSIONS 
In summarizing, it may be said that, although based on a relatively small 
amount of material incidentally collected, this study of Cardium presents several 
interesting features. 
1. The ring method of age determination may be applied to this species as well 
as to others previously studied. 
2. The growth of Cardium is characterized by great regularity, as shown by 
the individual growth curves presented. 
3. The type of growth observed in the razor clam is found in the cockle. In 
this form the relative growth rate falls throughout postlarval life as first noted by 
Minot in the guinea pig. The decline is orderly and regular, and in most cases the 
growth curve can be accurately fitted from the formula L = Be~ ce ~ k \ based on an 
exponential rate of decline of the relative growth rate. 
4. A comparison of growth in different localities shows the same relations as 
observed in the razor clam. The northern forms, in contrast to the southern, show 
a slower initial but more sustained growth and reach the greater age and larger size. 
