GROWTH AND MORTALITY OF PACIFIC RAZOR CLAM 
561 
The correlations of length with the other factors are the lowest. Large size is 
associated with great age, northern habitat, low early and high later relative growth 
rates. This lower correlation apparently reflects the fact that there is a lower per- 
cental variability in length than in any of the other factors. 
To summarize, we may say that the complex of environmental features on the 
southern beds produces a more rapid initial relative growth rate which more rapidly 
falls to a lower final value, and that the clams reach a smaller final length and have 
a shorter life span than on the northern beds. 
That these differing types of growth characteristic of the different localities are 
significant is indicated by their occurence in other cases. An example is furnished 
by the comparison of the growth of the two sexes at Hallo Bay, Alaska, where, as 
stated, slight sexual differences in size were observed. An inspection of Figure 4 
will show that the females grow more rapidly at first, but that by the third or fourth 
year the more sustained growth of the males has placed them in the lead, and that 
they reach a greater final length and outlive the females on the average by more than 
a year. Chamberlain obtained for one species of fresh-water mussel a sexual differ- 
ence in growth similar to that just described (1931). The results from other species 
of lamellibranchs are concordant. Thus in Cardium the differences of growth with 
latitude appear to parallel those found in the razor clam (Weymouth and Thompson, 
1931). It is not here possible to examine other groups but recent work on the life 
history of the striped bass in California by Scofield 3 has shown a difference in 
growth between the sexes essentially similar to that in the razor clam. 
Although the case is not comparable in detail, the findings of Gray (1928), who 
reared the eggs of Salmo jario at different temperatures, is interesting. Those 
developing at 15° C. grew far more rapidly but did not reach as great a weight as did 
those growing at 5° C. Gray points out that the yolk available for the metabolism 
of the embryo is limited, and must serve for both maintenance and growth. At the 
higher temperatures the life processes are pitched at a higher level and the fraction 
consumed in maintenance is greater, that available for growth is therefore less, hence 
the smaller size. Although there is no similar limitation of food material in the case 
of the clam, the observations are suggestive. 
BIOLOGICAL FINDINGS AND THEIR BEARING ON FISHERY REGULATIONS 
On the basis of the data presented in this and previous reports on the razor clam 
(McMillin, 1924, 1925, 1927, 1928; Weymouth, McMillin, and Holmes, 1925; Wey- 
mouth, McMillin, and Rich, 1931), the more significant biological findings may be 
summarized and their bearing on the question of fishery regulations pointed out. 
BIOLOGICAL FINDINGS 
These investigations have extended the applicability of the ring method of age 
determination to the razor clam. Work now in press (Weymouth and Thompson, 
1931), has shown that the same relations hold for the cockle ( Cardium corbis) and 
Chamberlain 4 has successfully applied the method to the fresh-water mussel ( Lamp - 
silis). There can be little doubt, therefore, that the ring method is of general validity 
for lamellibranchs and that in it we have a tool of great usefulness for the study of 
growth. 
3 Manuscript, in press. California Fish and Game Commission. 
‘ Thesis, Stanford University. 
