GROWTH AKD AGE AT MATURITY OF THE PACIFIC RAZOR CLAM 
215 
MORTALITY OF YOUNG 
Tlie preceding paragraphs give some idea of the great number of small clams 
that may settle in the sand in late summer as the result of a successful spawning 
year. The set is not equally hea\^' in consecutive years. Some years the young are 
very numerous, while at other times it is difficult to collect specimens enough for an 
examination. The abundant set of 1923 gave an excellent opportunity to study the 
mortality as well as the growth of these small clams during the first season. 
On August 1 the young clams, now only 0.25 centimeter in average length 
(about Yg inch), were foimd on the beach in groat numbers. From four counts the 
I.2S r3-2 
\ 
\ 
\ 
\ 
\ 
\ 
\ 
® 
\ 
V ^ 
• 
• 
/ 
<g— 
percentite 
1 August 
\ September 
October 
November 
December 
1 Uanuary 
February | 
/ 923 
19 24 
Fig. 10. — Showing the growth and mortality of small clams on the Copalls beach of Washington 
In 1923. Solid lines, read from scale on the left, indicate growth, showing rapid increase 
in size during August, soon after settling in the sand, and no increase during the winter. 
The brojsen line, referred to scale on the right, shows the decrease in numbers of small clams 
per square foot. The sudden drop in early December was due to a storm 
average number per square foot was found to be 1,451. In determining the distri- 
bution the clams were taken only from the top layer of the sand about 2 inches in 
thickness. The shifting of the sand may account for some errors, as Thompson 
(1919) has shown that the action of the surf on exposed sand beaches continually 
changes the topography of the beach. This was illustrated by the counts of Sep- 
tember 1 and 9, in which 986 clams per square foot were found on the first date, 
while 1,122 were found on the same area nine days later. 
As indicated by the figures just given, there was a steady decrease in the number 
of clams per unit area. By late fall they had been reduced to a third of the original 
42886—25 3 
