302 University of California Publications in Zoology [Vol. 22 



[San Francisco] Ferry Building and Goat Island Light" (Sumner, 

 et al., 1914, p. 22). The lower bay includes the remaining portion 

 south of this line. 



These three divisions, taken as a whole, manifest three rather 

 distinct sets of ecological conditions. 



The upper bay represents the brackish water environment, with 

 continually fluctuating salinity and maximum range of temperature 

 throughout the year. Receiving at its upper end the combined dis- 

 charge of the Sacramento and San Joaquin rivers, this segment of 

 the bay is very greatly affected by the inflow of so considerable a 

 quantity of fresh water. The interaction of run-off and tidal move- 

 ment produces a daily and almost hourly change in salinity, which 

 is altered further by variations in the width and depth of the channel 

 at different points, and by differences in the seasonal discharge of 

 the rivers, which is ordinarily more than five times as great during 

 the first six months of the year as during the last six months 

 (Grunsky, 1921, p. 14, etc.). In the Carquinez Straits the annual 

 range of variation in salinity is as great as from to 27 parts per 

 1000. Salinities at several points in the upper bay during 1921 are 

 graphically shown in the appended chart (fig. B). 



The middle bay exhibits a set of conditions nearly the opposite 

 of those just described. Its greater depth and volume and proximity 

 to the open sea make for a condition of high and fairly constant 

 salinity and for a minimum temperature fluctuation. Salinities at 

 two localities in this portion of the bay during 1921 are charted in 

 figure B. These are not, unfortunately, the localities of maximum 

 salinity, being considerably to the northward of the Golden Gate. 

 Records of the Albatross investigations during 1912-1913 show the 

 mean annual salinity at certain points in this area of the bay to be 

 as high as 30 and even 31 parts per 1000 (Sumner, et al., 1914, pi. 4). 



The lower bay represents an environment intermediate between 

 the two extremes just described. A great unbroken expanse of com- 

 paratively shallow water (mean depth 7.8 fathoms, as compared with 

 a mean depth of 14.8 fathoms for the sector of the bay between Goat 

 Island and Point Richmond), receiving no streams of any importance, 

 the lower bay presents a complex of conditions peculiar to itself. 

 The salinity is somewhat lower than that of the waters more proximal 

 to the open sea, though at the same time it probably is subject to less 

 daily and seasonal variation. Unfortunately, lrydrographic investi- 

 gations in this region have been extremely limited. The Albatross 



