476 



BULLETIN OF THE BUREAU OP FISHERIES 



^ 



Iand total departure of air temperature from normal for this period during these years 

 and also for 1922, 1923, and 1924. In Figure 28 the total monthly departures for 

 this 4-month period has been given because of the cumulative effect of water tem- 

 iperature on the development of the gonads during this interval. It can be seen 

 I'clearly that in 1922, 1923, and 1925 the water temperature was ahove normal, and we 

 iknow, because of the set obtained, that spawning in Long Island Sound was successful 

 (in these years. In 1924, 1926, and 1927 the water temperature was below normal 

 and setting was a failure This evidently was due to unsuccessful spawning, because 

 (virtually no oyster larva were found in the water. The success or failure of spawning 

 )in Long Island Sound apparently depends upon the quantity of eggs and sperm 

 jdeveloped by the oysters each year. Since fertilization of the eggs takes place outside 

 of the oyster and is a matter of chance, it is reasonable to e.xpect that the percentage 

 of eggs fertilized and number of larvae and spat produced will vary according to the 

 amount of spawn released. A small increase or decrease in the number of eggs or 

 spawn in a single oyster becomes of importance when we realize that it is midtiplied 

 by the number of oysters on the beds, which is from approximately 125,000 to 250,000 

 for each acre planted. 



It is lilcely that the fullness of gonad development is dependent on the amount 

 of food consumed by the oyster. We know that the process of feeding consists in 

 filtering water through the gills, and that the amount filtered is controlled by tem- 

 perature. Galtsoff has measured accurately the amount of water filtered by the 

 oysters at various temperatures. Taking his figures (GaltsofF, 1928), we can estimate 

 the differences in quantity of water filtered by the average oyster during cold or 

 warm seasons. The period in which we are interested extends from the beginning 

 of feeding (about April 15, when the water temperature reaches 7° C) until the time 

 of spawning (the latter part of July). During this period the approximate number 

 of liters or quarts of water filtered by an average oyster at normal water temperatures 

 is given in the following table: 



Table 11. — Approximate quantity of water filtered by an average oyster at normal water temperature 



1 15 days only. 



As a result of the monthly and annual variations in water temperature that 

 occurred from 1922 to 1927, the quantity of water filtered shows a corresponding 

 variation, which is presented in the following table: 



