PROGRESS IN BIOLOGICAL INQUIRIES, 1935 433 



OYSTER IN\'ESTIGATIONS IN WASHINGTOX STATE 



Most of the work carried on at the Piiget Sound Laboratory by 

 I>i\ A. E. Hopkins has been a continuation of the plan of study 

 on the problems concerning the Olynipia oyster, Osirea lurlda^ and 

 is inseparable from the general results obtained and recorded since 

 the investigation was undertaken in 1931. The purpose of this in- 

 vestigation was to make a study of the factors influencing spawning 

 and setting of the Olympia oyster in order to develop a system 

 whereby oyster growers could be assured annually of an abundant 

 supply of seed. Therefore, studies were made of spawning habits, 

 larval life, and the attachment of the larvae. 



Thermograph records of water temperatures taken continuously 

 over a period of 5 seasons indicate that 13° and 14° C, the average 

 temperatures of the water in which Olympia oysters begin to spawn 

 in the spring, may not be called the critical temperature for some 

 sj)awning takes place above and below this temperature range. 



It has been found that after their discharge from the maternal 

 brood chamber the larvae swim freely for a period of from 20 to 41 

 days, depending upon water temperature. 



The relative number of spat caught daily per unit of cultch was 

 obtained for each of the past 5 summers as follows: Wire baskets 

 containing shells were planted throughout each season, allowed to 

 remain in the water for a few days, and the collected spat counted. 

 It has been found consistently that the setting of larvae occurs in 

 w^ell-defined periods directly correlated with tidal cycles. Typically 

 setting is heaviest during a run of extreme minus tides. Experi- 

 ments show that most of the larvae attach upon the flood tide, few at 

 the ebb tide during this period. Very little setting occurs during 

 neap tides. Thus, within certain limits, the waves of setting are pre- 

 dictable merely from the tide tables. On the basis of such results, 

 oyster growers were advised as to the time to plant cultch for the 

 collection of seed, and it is generally agreed that the industry has 

 benefited materially by this assistance during the past several years. 



Continued study of the effect of changes in salinity on the rate 

 of feeding of the Japanese oyster have further shown these quan- 

 tities to be directly correlated. When the salinity falls below ap- 

 l^roximately 13, the oyster appears to be unable to pump water. 

 Above this level, within limits, the rate of pumping increases directly 

 with salinity. These experiments provide the much-needed infor- 

 mation about the effect salinity may have on transplanted oysters. 



A study was begun on the spawning and setting habits of the 

 Japanese oyster, which has recently become established on the Pacific 

 coast. While the temperature of the waters in this State is in 

 general somewhat too low for successful natural propagation of this 

 species, it is evident that scientific investigations may show it pos- 

 sible for growers to produce their own seed instead of importing it 

 from the Orient. In the summer of 1935 an investigation was 

 begun to lay the foundation for a more extensive study of this 

 problem during the next few years. 



A matter requiring immediate attention is the Japanese oyster 

 drill which, unfortunately, has been introduced into several waters 

 in the State of Washington, and in one locality has done tremendous 



