The American Oyster Drill, Urosalpinx Cinerea (Gastropoda): Evidence Of Decline in an Imposex-Affected Population (R. Blackwater, Essex)

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Abstract
The American oyster drill, Urosalpinx cinerea introduced to UK waters around the turn of the century, flourished in the Essex oyster grounds until the 1970s. Recent observations, 1987–1990, made in Goldhanger Creek, River Blackwater, indicate that the population level has been reduced to the point of scarcity and that those individuals remaining are old. All females examined exhibited imposex. In most, this masculinizing syndrome was developed to an advanced state that involved oviducal malformation; copulation and egg capsule formation are thought to have been inhibited and hence such affected females were sterile. Other, probably very old, females appeared infertile because of senility. No viable spawn was observed during the four summers of 1987 – 1990.