228 
BULLETIN OF THE BUBEATJ OP FISHEBIES 
centimeters were found, and all clams more than IOV2 centimeters were mature. 
The size at which 50 per cent were mature (9.75 centimeters) was taken as the 
size at maturity. At Swickshak clams are first mature at 8V2 centimeters, and 
all above 111/2 centimeters are mature, maturity (50 per cent) being at 9.91 centi- 
meters. All clams from the Washington beach spawn when they are 2 years old. 
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Age in Yean 
Pig. 19. — Showing portions of tliree growth curves and points at which 50 per cent, by age, 
and 50 per cent, by size, are mature on each bed (points W, 8, and C). For the Swickshak 
material, Sio, 8, and Sm represent the points at which 10, 50, and 90 per cent, respectively, 
by both age and size, become mature 
Since all mature at the same age, the median length of these at spawning time 
has been taken as the size at maturity. 
Thus in order of size the lengths at maturity on the different beaches are as 
follows: Cordova, 9.75 centimeters; Swickshak, 9.91 centimeters; Washington, 
10.30 centimeters. At the rate at which the Washington clams were growing at 
