426 U. S. BUREAU OF FISHERIES 



Comparison of results witli traps containing seed oysters and 

 those containing clam and oyster shells showed that the former are 

 seven times more efficient for catching those pests. A total of 80,838 

 drills of both species were removed from 60 acres of oyster beds, by 

 hand picking, on the tidal fiats at Wachapreague and vicinity. 



Beds that have been cleaned and replanted with seed oysters can 

 be protected against invasion of drills from surrounding bottoms by 

 leaving an nnplanted zone, approximately 20 feet wide, around the 

 replanted area and surrounding the outer edge of this zone with a 

 continuous line of traps set at 5- to 8-foot intervals. This method 

 when tested on a commercial scale, showed an average collection of 

 5,760 drills per 25 traps over a period of 8 w^eeks. Subsequent 

 examination of the seeded area showed an almost complete absence 

 of drills, thus indicating that trapping operations of this type are 

 of practical value for the protection of oj^ster beds. 



It is clearly evident that the drill is a serious oyster pest, of such 

 economic importance as to justify the immediate adoption and ex- 

 tensive application of control measures of the type outlined by the 

 present investigation. 



Two species of oyster drills occur in this region, namely Urosal- 

 pinx cinerea and Eupleura caudata, the former being considerably 

 more numerous and destructive to oysters, comprising over 78 per- 

 cent of the number collected. Prolific reproduction of Urosalpinx 

 was observed in the heavy deposition of egg cases during June and 

 July and the more or less continuous spawning of this species over 

 a period of 71/2 months. Egg cases of Eupleura were found in only 

 three instances in numerous examinations of natural and planted 

 beds. 



Studies of the distribution, abundance, and possible control of 

 oyster pests in the principal beds in Pamlico, Core, and Bogue 

 Sounds and their tributaries in North Carolina were conducted in 

 cooperation with the North Carolina Department of Conservation. 

 In Core and Bogue Sounds where the salinity is high, ranging from 

 27.16 to 35,61 parts per mille, the destruction of 14 to 68 percent of 

 spat and seed oysters by drills and 60 to 90 percent of adult oysters 

 by boring sponge, was observed on beds located below low water 

 mark. Drills were found to be most abundant on public beds in 

 the vicinity of Harbor Island and Atlantic where 13 to 22 specimens 

 were collected per bushel sample. By means of trapping operations 

 a total of 10,755 drills were removed from these areas over an aver- 

 age fishing period of 4 weeks. In one locality an unusual catch 

 of 3,238 drills was made with 100 traps in 1 week, of which approxi- 

 mately 94 percent were young specimens measuring from 3 to 14 

 millimeters in length. This particular area had been restocked the 

 previous year with culled seed oysters from drill infested beds near 

 Portsmouth, thus demonstrating how transportation of Q,gg cases 

 of this pest may cause its spread to other beds. 



Field investigations were conducted from June 15 to October 15 

 along the western shore of the Chesapeake Bay in cooperation with 

 the Virginia Commission of Fisheries. Observations at 245 stations 

 showed the drill to be abundant throughout this region. An average 

 of 9 drills and 35 egg capsules were found per bushel of oysters. 

 Drills were most numerous in lower portions of the bay and rivers 



