Stauber (1943) relates that a ground in Delaware Bay was planted heavily 

 with small oyster seed in May, and during the summer additional oyster spat . 

 catches amounted to 49 spat per shell. Although drill trapping was begun soon 

 after spatting began, most of the summer spatfal! was destroyed and the original 

 spring planting was much reduced by drills . In a second instance in the same bay 

 an oyster farmer obtained a heavy spatfall of oysters (91.6 spat per shell) on 

 cultch planted on an isolated ground . By the end of October at least 65% of the 

 spat were drilled, and soon after most of the set was a total loss . 



Newcombe and Menzel (1945) report that in 1944 more than 40% of the 

 oysters on Nansemond Ridge, mouth of the fames River, Virginia ; were killed 

 by drills; and that on the Sea Side it is not uncommon to find a 70% mortality. 



Mackin (1946) observed that 75 to 83% of the oyster spat in Wachapreague, 

 Virginia; were destroyed by Urosalpinx between June and December . 



hi eastern Canada on one heavily drill infested oyster ground at Malagash, 

 32% of the oysters present were destroyed in one summer. 



Cole (1951) notes that in Essex rivers, England,, approximately 75% of 

 English oyster spat present are destroyed during the first year of life. 



Mistakidis (1951) found an average of 1 .75 drills per square meter on an 

 English oyster bottom in a poor state of cultivation, and using Cole's (1942) 

 figure of ,9 spat destroyed per drill per day, has calculated that during a period 

 of three months in the summer this concentration of drills feeding at this rate on 

 a 15 acre ground would destroy a maximum of 8, 840, 000 oyster spat. 



Engle (1953) reports a case in Tangier Sound, Maryland, at a time when 

 drills were abundant and salinities high in which 50% of the seed oysters planted 

 in April were destroyed by drills by July, and 100% by October of the same season. 



At the Institute of Fisheries Research pier s Morehead City, North Carolina, 

 Chestnut and Fahy (1953) found that 23 spat in a total of 516 spat collected on ex- 

 perimental cultch near the bottom were drilled by Urosalpinx. 



RELATION TO ENVIRONMENTAL FACTORS 

 Substratum 



Studies in which the distribution of the oyster drill has been related to the 

 nature of the substratum appear to agree rather consistently that soft muddy bottoms 

 devoid of shell, stone, living epifauna, and ether hard objects are unfavorable for 



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