126 U.S. BUREAU OF FISHERIES 



For some reason, in Mud Bay the results obtained were entirely 

 different, although the conditions of salinity and temperature in the 

 two bays differ only very slightly. In Mud Bay there were four 

 relatively small waves of setting. The duration of these was as 

 follows: (1) July 6 to 23, (2) July 24 to August 5, (3) August 13 to 

 23, and (4) August 24 to 30. In the same order, the number of spat 

 obtained per bag of shells during the peak of each of these periods 

 was: 1,500, 1,200, 500, and 400. While in Oyster Bay the larvae 

 continued setting up until about the middle of October, in Mud Bay 

 after the first of September practically no further set was obtained. 

 The method of planting cultch at present employed by the oyster 

 growers is apparently based on the assumption that only one setting 

 period normally occurs, for cultch is always planted in June. During 

 two seasons it has been found that in Oyster Bay the second period 

 of setting taking place in August is as great as the first. It has been 

 suggested that oyster growers attempt to take advantage of the 

 second as well. 



A new type of spat collector, a modification of the common egg- 

 crate filler, which provides a large amount of horizontal surface, was 

 put into commercial use during the season. These apparently were 

 highly successful and in every case obtained a most excellent catch 

 of spat. 



Prehminary experiments were made to determine at what tides 

 larvae set most abundantly. It appears to be a common opinion 

 that the water most favorable for setting is that retained in the dikes 

 at low tide. By planting glass plates for periods of a few hours at 

 a time, it was shown that less spat are caught at low tide than at 

 any other time, that setting takes place primarily on the flood and 

 high tides when the water is from 8 to 10 feet deep. Further tests 

 will be made on this matter next season to clear it up more thoroughly. 



An experimental study of the effect of temperature on the feeding 

 of the Japanese oyster was made. It was found that the rate at 

 which the oyster pumps water depends upon the degree of openness 

 of the shells, that the shells are themselves dependent upon tempera- 

 ture and remain open widest at a temperature of approximately 

 20°C. The gills seem to pump most rapidly at a temperature above 

 25°. However, as the temperature rises obove 20°, the shells tend 

 to close more and more, reducing the effectiveness of gill activity. 

 More water is pumped by the average oyster at 20° than at any 

 temperature either above or below. Apparently the Japanese oyster 

 can pump water at a temperature as low as 2°C. 



Oyster investigations in California. — At the request of the State 

 Division of Fish and Game, H. C. McMillin has been detailed to 

 assist the State authorities in developing the California oyster indus- 

 try. At present extensive areas of inshore waters in California 

 remain barren while the oysters are shipped in from the east coast or 

 from the State of Washington. Small areas in San Francisco and 

 Tomales Bay have been used for some time to hold imported oysters 

 until they were marketed, but no attempts have been made until 

 recently to cultivate and grow oyster seed. 



Three species of oysters are available for use in California waters: 

 The native oyster (0. lurida) found in natural beds in many small 

 channels; the eastern oyster {0. virginica) transplanted from the 

 Atlantic coast; and the seed of the Japanese oyster {0. gigas) imported 



