80 



The salinity in Carquinez Strait increases from Suisim to San 

 Pablo Bays, which it connects. As shown in the graphs of last year's 

 report (plate 36), it is generally about two and sometimes five parts 

 per thousand higher at the upper than at the lower end. Crockett 

 lies near the lower end, about one mile above Vallejo Junction and the 

 Carquinez Straight Light on the opposite side. The increase in salinity 

 at comparable tides between Carquinez Straight Light over that at 

 Crockett is therefore small, probably less than 1 part per 1000. For 

 practical purposes salinities at Crockett at the surface present ap- 

 proximately the survival level. 



The following table analyzes the salinities at low tide, or the period 

 of maximum freshness of the water, at Crockett. Unfortunately we 

 have no records at high tides, when Teredo might be expected to avail 

 itself of water of higher saline content for respiration and feeding. 

 An additional complication in introduced by the fact that the days 

 of minimum salinity at low tide which occur at the spring tides are 

 also those of maximum salinity at high tide. 



TABLE 10 

 Conditions of .Respiration ami Feeding for Teredo at Crockett, 



Parts 



per 



1000 



15 



14 



13 



12 



11 



10 



9 



8 



7 



6 



5 - 



Nov. 19, 192O to April SO, 1921 



Salinities at low tide, surface 



Avg. days 



No. of Days at Days between 



periods or above below periods 



1 

 1 

 1 

 1 

 2 

 2 



3 

 7 



10 

 10 

 14 

 15 

 17 

 13 



1 

 1 



2 

 2 



4 

 5 

 7 



12 

 20 

 26 

 41 

 55 

 85 

 109 



162 

 162 

 161 

 161 

 159 

 158 

 156 

 151 

 143 

 137 

 122 

 108 

 78 

 54 



79.5 



79.0 



52.0 



21.6 



14.3 



13.7 



8.7 



7.2 



4.6 



4.1 



Greatest No. 



days between 



periods 



103 

 102 

 102 



71 

 40 

 27 

 25 

 18 



According to the table there were at Crockett from November 19 

 to April 30 in surface waters, 13 periods averaging 4.1 days in length 

 and totalling 54 days, with salinities of less than 1 part per 1000, with 

 a maximum length of 5 days. Below 2 parts the maximum length was 



