STUDY OF FOOD PREFERENCE AND RATE OF FEEDING 

 OF JAPANESE OYSTER DRILL, Ocinebra japonica (Dunker)^ 



by 

 Kenneth K. Chew 



ABSTRACT 



Two experiments, of 70 days each, were conducted to determine 

 food preference of the Japanese oyster drill, Ocinebra ( = Tritonalia) 

 japonica. Individually marked drills were presented with a choice of 

 four different food organisms: bay mussels, MytiltCS eduHs; Manila 

 clams, Venerupis japonica; Olympia oysters, Ostrea lurida; Pacific 

 oysters, CrasSOStrea gigas. Daily observations were made on the 

 location of each drill and the food animal being attacked. 



The Japanese drills, which were originally collected fronm Pacific 

 oysters, preferred either Manila clanas, Olympia oysters, or bay 

 mussels to Pacific oysters. Most of the drills attacked the same 

 species of food organism attacked previously, and did not move to 

 another organism of a different species. 



Ocinebra usually took 4 to 5 days to drill and to finish feeding on 

 bay mussels; 5 to 6 days for Pacific oysters; 6 to 7 days for Olympia 

 oysters; and 7 to 8 days for Manila clams. The duration of attack by 

 drills appeared to be related to the thickness of the shells of the prey. 



THE PROBLEM 



The Japanese oyster drill, Ocinebra 

 (= Tritonalia) japonica (Dunker), is con- 

 sidered by oyster growers of the Pa- 

 cific coast to be potentially the most 

 serious predator on Pacific (Cras- 

 SOStrea gigas) and Olympia oysters 



1 Contribution No. 44, College of Fisheries, University 

 of Washington, Seattle, Washington. 



Note. --Kenneth K. Chew, Fisheries Research Assistant, 

 College of Fisheries, University of Washington, Seattle, 

 Washington. 



(Ostrea lurida). Ocinebra was intro- 

 duced to the Pacific coast of America 

 with the importation of Japanese seed 

 oysters (Galtsoff, 1929). This drill has 

 beconae well established in several 

 bays of Puget Sound in the State of 

 Washington (Galtsoff, 1932). It has 

 also been found to occur in the water 

 along the Canadian Pacific coast (Elsey, 

 1935), as well as in California and 

 Oregon oyster growing areas. 



Although Ocinebra japonica has been 

 found to drill oysters with resultant 



