1^1''] Barrows: Shipworm in San Francisco Bay 33 



The average monthly discharge from this double river system, 

 which of course varies with the rainfall and melting of the snow over 

 the watershed of the rivers, is given as follows (Sumner, et al., 1914, 

 p. 78). 



MEAN MONTHLY DISCHARGE OF SACEAMENTO AND SAN JOAQUIN 



RIVER SYSTEMS 

 Based Upon Records For Ten Years 



The months of maximum discharge of fresh water are seen from 

 this table to be April and May, and it is during these months that we 

 should expect the salinity of San Pablo Bay to be at its minimum. 

 The months of least discharge of fresh water are the fall months of 

 August, September, October, and November, and it is during these 

 months, constituting one-third of the year, that we should expect the 

 salinity of this bay to be at a maximum. The seasonal increase in 

 the amount of fresh water discharged and the corresponding decrease 

 in the salinity of this part of the bay begins during December and 

 becomes marked during the month of January. It is to be noted in 

 this connection that shipworms M^ere found dead in the later part of 

 January, 1914, in certain test piles which had been taken up early in 

 the month and moored for a few weeks alongside the dike which had 

 been infested with the borers. This may have been due to the influx 

 of a large amount of fresh water into this part of the bay during 

 that month as the first of a discharge of considerably more than even 

 the normal amount for that month during the rainy season of 1913- 

 1914, or possibly to heavy jarring of the pile when removing it. 



Salinity of San Pablo Bay. — From this varying discharge of fresh 

 water into San Pablo Bay it has been found, as was expected, that the 



