422 U. S. BUREAU OF FISHERIES 



TJrosalpinx and Eupleura, wliicli constitute a serious menace to oyster 

 production, causing a loss to the Delaware Bay oyster industry of 

 approximately $1,000,000 a year. 



Headquarters were established at Bivalve, N. J., with a field station 

 at Cape May, N. J., whei-e the State of New Jersey maintains an 

 oyster experiment laboratory. Still another station was in operation 

 during June, July, and August at Barnegat Bay, N. J., where studies 

 were made on the activities of the drills with relation to changes in 

 environmental conditions. The cooperation of the State of New 

 Jersey, both hy a generous offer of laboratory and office facilities, 

 and by the use of its personnel and equipment, made possible a much 

 broader and a more thorough study on the biology of the drill and 

 the methods of its capture than would have otherwise been possible. 



The work was carried out in cooperation with Dr. Thurlow C. 

 Nelson, by Dr. Sizer, J. B. Engle, and H. H. Haskin. The State 

 W. P. A. branch generously cooperated with the Bureau of Fisheries 

 project by assigning 10 relief laborers for the construction and hand- 

 ling of drill traps, and by providing the boat for trapping experi- 

 ments. Because of the seriousness of the drill problem in Delaware 

 Bay, the work was carried out throughout the year and valuable 

 information was recorded on the behavior of the drills during the 

 winter months. 



Two methods of controlling drills were attempted in Delaware 

 Bay. One was the use of a chicken-Avire bag trap that could be 

 hauled to the surface at regular intervals, making use of the habit 

 of the drill to climb upon any elevated portion of the bottom to feed 

 and lay eggs. By using 3,500 traps for a period of 6 months, a total 

 of approximately 1,300,000 drills were caught. To attempt control on 

 a commercial scale, traps were concentrated in areas where tests 

 showed the densest population. The traps were baited with young 

 oysters and rebaited as often as needed, about once a month, and at- 

 tached by snoods to a line of copper oleated rope, about 50 traps to a 

 line. Four to six of these lines were placed at a station and tended 

 weekly. 



The other method of control developed during the course of the 

 investigation consisted in dredging the bottoms with a drill dredge, 

 especially designed to make it economical and available to the com- 

 mercial oysterman. It is operated practically the same as an oyster 

 dredge. 



The combination of trapping with wire bag traps and the use of 

 the drill dredge is considered a practical and efficient means of 

 oyster drill control for Delaware Bay. 



Since the knowledge of the life liistory and behavior of any 

 destructive animal is essential for the operation of control measures, 

 a comprehensive study was made of the habits, migration, and 

 propagation of the drill. 



A series of experiments was conducted on the migration of drills 

 under varying conditions of temperature, salinity, and bottom. "Re- 

 sults showed that drills are influenced in the direction of their 

 migration by the position of food, that they move at a rate of at 

 least 150 feet in 48 hours in the direction of food, and against 

 prevailing currents. These migrations were performed over a bot- 

 tom of loose sand and mud devoid of oysters or shells. The drill 



