Bay encounteied drilled oyster spat as small as 36 mm. in diameter which 

 had not yet produced dissoconch shell He corroborates Pope's conclusion that 

 large numbers of young spat may be dnlled : and this may in part explain the 

 apparent disparity frequently encountered between plankton counts of oyster larvae, 

 counts of newly attached oyster spat and subsequent densities of seed oysters 

 According to Cole in England; where Uro salpinx has become a serious menace 

 much of the damage it inflicts on the oyster beds passes unrecognized since the 

 shells of small spat up to thumb nail size ; one of its chief prey are easily swept 

 off the cultch and broken up. He states that there is evidence that the drill 

 annually destroys very large numbers of tiny spat within a few weeks of settle- 

 ment. In plunger jars in the laboratory he determined thattfrirfs averaging 3.5 

 mm. m height may destroy 9.7 oysters varying m diameter from 3 to 7 mm. per 

 drill per week at a temperature of 20° C. Engle (1940 ; 1953) also demonstrated 

 a high rate of destruction of very young spat by young drills . 



Table 9. The Relation of Water Temperature and 

 Drill Size to the Rate of Destruction of 

 Oysters by Uro salpinx cinerea 

 (Modified from Engle, 1953) 



Average Number of 1 inch Oysters 

 Destroyed per Drill per Month of 



the Following Heights 



Temperature 



16-20 mm. 21-24 mm 25-27 mm. Range °C 



1.3 1 6 2.1 13.2 16.2 



24 3.7 4.9 16.2-18.5 



3,3 4.4 5 2 18.5-22.5 



78 11.1 22.5-23 5 



A number of estimates on the seasonal damage imposed by Uro salpinx have 

 been reported Federighi (1931c) from data collected in Beaufort ; North Carolina, 

 reports that ore drill can kill from 30 to 200 oysters in a season depending or 

 their size. Galtsoff et al. (1937) state that in New Jersey a single drill can kill 

 over 300 very young spat per season, or " . . may devour on the average 34 

 adult oysters per week . . . " . The data in the quotation refer not to adult oysters 



56 



