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FISHERY BULLETIN: VOL. 72, NO. 3 



SPAWNING LIU SPENT 



MALE 



1- 60 



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cc 



Ui 



a 40- 



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FEMALE 



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NOV DEC 

 1970 



FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC I JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV 



1971 I 1972 



Figure 4. — Male and female reproductive cycles of the soft-shell clam, Mya arenaria, during 1971 and 1972 from Skagit Bay, Wash. 

 The length of each shaded area represents the percentage frequency of clams in each reproductive phase. A total of 1,739 clams (48% 

 males and 52% females) were examined during the 2-yr study. y 



The smallest mature male clam examined dur- 

 ing the 1971 reproductive cycle was 22.9 mm in 

 length, and the smallest female 31.0 mm. Both 

 were taken in the September sample and were in 

 the inactive phase. The largest immature clam 

 was collected in late May and was 45.2 mm in 

 length. 



1972 Reproductive Cycle 



The 1972 reproductive cycle (Figure 4) was 

 similar to 1971 with the exception that the cycle as 

 a whole began earlier and the active phase was of 

 longer duration. Active female clams first ap- 

 peared in November 1971 and active males in 

 December 1971. The active phase lasted until May 

 1972. During the period from February until April 

 the majority of all clams sampled of both sexes 

 were in the active phase. 



Ripe male clams first appeared in April and ripe 

 females in May. Ripe clams of both sexes, 78% of 

 the males and 49% of the females, were most 

 abundant in May. 



Spawning commenced in late May and peaked 



in June for both males (86%) and females (65%) 

 and then continued at a diminished rate until 

 September. 



Spent clams of both sexes were present from 

 June through October. They were most abundant 

 in September when 45% of the males and 72% of 

 the females were in the spent phase. 



Inactive male clams first appeared in July 

 (10%), while inactive females first appeared in 

 September (13%). The highest percentage of inac- 

 tive clams occurred in October with 79% of the 

 males and 70% of the females in the inactive 

 phase. 



As in 1971, the spawning cycle for most of the 

 clams under 60 mm in length commenced about 1 

 mo later than the normal cycle and ended 1 mo 

 earlier. The smallest mature clam collected was a 

 36.3-mm spawning male obtained in July. The 

 smallest mature female was 38.9 mm in length 

 and was in the active phase in March. The largest 

 .immature clam was 51.5 mm in length and was 

 collected in March. 



In 1971 spawning was quite complete in both 



654 



