Sexual Maturity 



According to available but not always complete information the oyster 

 drill attains sexual maturity at ages varying from one to three years and heights 

 of 13 to 24 mm. in different regions. Pope (1910-11) in Woods Hole, from field 

 observations states that sexual maturity apparently occurs at the age of one year. 

 He found females about 13 mm. in height, the size attained at the end of one 

 season, depositing egg capsules early in June . 



On the basis of field experiments in Delaware Bay Stauber (1943) con- 

 cludes that sexual maturity is not reached at least until 15, and possibly 25, 

 months of age, at a size of more than 15 mm. in height. In April when the 

 temperature of the water had not yet reached 14° C he confined two sets of 

 drills in cages with oysters at the low water line . The height range of the drills 

 in the first cage was 11-15 mm., and in the second cage, 21-30 mm. By August 

 the drills had grown to heights of 16-24 mm . and 23-30 mm . respectively. Al- 

 though the larger drills oviposited 895 egg cases during the summer, the smaller 

 drills deposited no egg cases . By October 10 one cluster of egg cases was found 

 in the cage of the smaller drills indicating that the larger drills therein had now 

 reached sexual maturity. Because of their small size Stauber states that the 

 smaller drills when confined in April, 1939, were either 9 months old (derived 

 from the early 1938 summer hatching) or possibly 19 months old (from the late 

 1937 summer hatching) . The smallest isolated drill to oviposit in Stauber's 

 other experimental cages measured 16.5 mm. in height. 



By confining Urosalpinx in cages with barnacles in English waters Cole 

 (1942) determined that females start depositing eggs when not much smaller than 

 24 mm . in height at an approximate age of two years, but the number of egg cases 

 oviposited is slight . At the start of the breeding season he noticed that the majority 

 of females 22 mm . or less in height contained undeveloped gonads and immature 

 accessory reproductive organs . From these data and field observations he con- 

 cludes that full spawning in English waters does not begin urtil drills are three 

 years old. The differences reported in the age and size of drills at sexual 

 maturity in different regions may express not only incomplete information but 

 the existence of different geographic races . 



Longevity and Mortality 



Cole (1942) from his size frequency curve and growth mark studies con- 

 cluded that the approximate duration of life of LL cinerea i n English waters is 

 10 years, and that occasionally drills as old as 13 or 14 years are encountered. 



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