74 



TABLE 8 



First Settlement of Teredo in San Francisco Bay and 

 Corresponding Salinities, 1921 



Mean salinity 



Location of Date of first for 5 days preceding, 



test timber settlement parts per 1000 



Dumbarton July 20 



Goat Island Aug. 15 



Oakland Harbor Light Aug. 15 



Black Point Sept. 15 24.3 



Mare Island Strait Aug. 26 



Crockett Aug. 8 21-1 



Port Costa Aug. 23 20.3 



Benicia Sept. 22 



Martinez Nov. 15 17.9 



Rowe Island Light Nov. 15 



It appears from these records that the breeding season of Teredo 

 began several months later in 1921 than in 1920 or that larvae of 1919 

 survived to a later date in 1919-20 than in 1920-21. Data are lacking 

 to determine with certainty which of the two conditions prevailed. The 

 lower salinities of the winter of 1920-21 might explain the delay in Car- 

 quinez Strait, but not elsewhere in the Bay region. It is possible that 

 temperatures might explain this contrast, but unfortunately we have 

 complete records only of air temperatures, not of those of the Bay 

 waters. The spring season of 1921 was delayed and vegetation showed 

 the depressing effect of the prolonged lower temperatures. 



Factors Limiting the Persistence and Distribution of Teredo navalis 

 in San Francisco Bay in 1921 



The adequate determination of the environmental conditions which 

 limit the persistence and inhibit the extension of Teredo navalis in San 

 Francisco Bay will require much more investigation than has been thus 

 far accomplished. Certain facts bearing on these problems are here 

 presented as a progress report, since they may be of value in the con- 

 sideration of preventive measures here and elsewhere. 



Two distinct phases of these problems suggested themselves for in- 

 vestigation in our locality. The first is the relationship of salinity to 

 the survival of Teredo in Carquinez Strait, where summer salinities 

 are high, permitting the rapid growth and even more startling invasion 

 of this pest, and where salinities during the winter months are greatly 

 reduced. This problem is complicated by the fact that the period of low 

 salinity coincides with that of the seemingly normal annual dying off 

 of many individuals here and elsewhere, and is still further compli- 

 cated by other environmental factors, such as changing food supply and 

 disease. The lowered salinity is therefore only one of several factors 



