stated untiJ more observations are made No one has yet attempted to follow 

 marked drills in the spawning migration . 



Stauber (1943) has clearly demonstrated during his successive years of 

 drill trapping in Delaware Bay that drills inhabiting deep water bottoms some 

 distance from intertidal areas also exhibit a pronounced prespawnmg locomotory 

 activity which he calls the "pre -egg laying activity" This may be similar to that 

 expressed by drills migrating inshore , Using the number of drills captured per 

 rrap per week as an index of activity, Stauber obtained a marked rate of activity 

 in May when the temperature of the water normally rises from 15 to 20°C in 

 Delaware Bay. This peak of activity subsides conspicuously with the onset of ovi- 

 position even though the temperature of the water continues to rise for about. 6 

 weeks more, and is not usually equalled again until July or August when young 

 drills of the current season, which make up as much as 25 to 50% of the total 

 catch, start moving into the traps . 



It should be emphasized diat it is not known how far drills will travel 

 during the inshore summer migration , nor has it been definitely proven that 

 these migrations occur for spawning purposes alone. It is possible that the migra- 

 tions express the negative response of drills to gravity at summer temperatures 

 in much the same way that in deeper water they crawl onto elevated objects, and/or 

 that drill population pressures add impetus to the migration. Finally, since some 

 drills may bury in intertidal sediment over the winter, not all drills appearing 

 intertidally in the summer may represent deep water migrating Urosalpinx. 



"Sudden Appearance" of Drills on Oyster Grounds 



The "sudden appearance" and unexplained origin of high concentrations of 

 drills on oyster bottoms is reported by oyster growers from time to time. The 

 writer agrees with Stauber (1943) that these phenomena appear to have a rather 

 simple biological explanation . 



Stauber (1943) demonstrated in Delaware Bay that even so-called vacant 

 oyster bottom retains some drills and that grounds dredged free of market oysters 

 in the winter may be infested with appreciable quantities of drills. In either case, 

 as is generally the commercial practice, seed oysters are planted on these 

 bottoms in the spring before the peak of oyster drill oviposition and supplement 

 the food supply of the drills . During the summer the hatching drills also find 

 added food on the newly planted seed oysters which regularly catch quantities of 

 oyster spat ; barnacles, and other sessile organisms. As a consequence the 

 survival of the small snails is high, but the oyster grower who does not always 

 carefully search for the pests and who uses only the ordinary oyster dredge as 



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