month the temperature of the water dropped gradually from 24.2 to 16. 4° C, and 

 by the end of the second month, to 10° C. The tidal currents flow north and south 

 over this bottom. In the two months of trapping only 4% or 81 of the marked 

 drills were recovered. Ten of these were captured between the 7th and the 11th 

 days, suggesting (if the drills travelled in straight lines . . . .which is not generally 

 the case) that they moved roughly 400 feet in 7-11 days, or 36 to 57 feet per day. 

 The maximum catches of drills occurred 19 to 26 days after the marked drills 

 were released, connoting a migration rate for the majority of the recovered drills 

 of 15 to 21 feet per day, Although 63% of the total number of drills recovered 

 moved southward toward oyster plantings, 7.4% moved west toward bottom with 

 but a few oysters and at right angles to the flow of the currents, and 9 9% moved 

 east and 19.7% moved north both to areas devoid of oysters. 



Needier (1941) states in summary of his observations which he does not 

 describe that drills in Canada move only an average of 10 to 15 feet in a month, 

 that they show no definite horizontal migrations, and that they spread quickly only 

 if carried. 



In his drill trapping operations Stauber obtained much information on the 

 spottiness of drill densities over large areas of the bottom in Delaware Bay. This 

 was particularly evident on adjacent grounds on which drill food supplies differed 

 strikingly over long periods of time, and confirmed Federighi's earlier observa- 

 tions on similar irregularities in the distribution of the drill. One of Stauber' s 

 many examples will suffice: In 1936 he trapped three contiguous sections of 

 bottom: the first held small oysters planted two months earlier; the center, old 

 oysters planted four years earlier; and the third, oysters planted two months 

 earlier but slightly larger than those in the first section. Traps, baited with 

 freshly collected brackish water oysters, were tended weekly from July to September, 

 and yielded insignificant differences among the three sections. On the basis of 

 Haskin's (1950) results it would be postulated that drills on the large oysters would 

 tend to migrate to the younger oysters . This apparently did not occur . In South 

 Carolina Lunz (pers. com ) also finds an extremely spotty distribution of drills; 

 some oyster beds are inhabited by drills while nearby grounds with apparently 

 identical conditions are not infested. Newcombe and Menzel (1945) also report 

 much variation in the concentration of drills from ground to ground. 



Stauber has summarized additional information which tends to minimize the 

 extent of migration by Uro salpinx. He found in drill dredging operations that the 

 proportion of^ drilled Urosalpinx shells increased with the increased degree of 

 barrenness of~bottoms . He observes that it is difficult to reconcile such cannibal- 

 ism with the maximum migratory rate reported by Galtsoff et al (1937) and the 

 relative proximity of oysters on adjacent bottoms . 



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