288 
BULLETIN OF THE BUREAU OF FISHERIES 
from the mouth to the head the several lines extending across the bay, we find the 
following : 
Salinity data for the line G, F, E during 9 of 1 1 cruises showed that the surface 
salinity was higher on the east side 5 ’ 6 ; line D, C, B, A, 13 of 13 on the east side; 
fine H, H', Q, 0, 16 of the 16; fine J, I, K, 12 of the 13; fine N, M, N', 10 of the 12; 
line P, L, L' , 10 of the 11 ; R', R, 11 of the 11 ; line T, S, 9 of the 11 ; line V, W, X, 8 
of the 14; and line Z, Y, 9 of the 15®. It will be noted that toward the head the 
condition mentioned gradually changes until along the line Z, Y the higher surface 
salinity occurs on the east side with considerably less frequency. 
BOTTOM SALINITY AT MOUTH AND HEAD 
In this discussion of the bottom salinities it should be understood that samples 
from the same area collected on different cruises were not taken at exactly the same 
depth and that when comparisons are made between bottom salinities in different 
parts of the bay it is done merely to show under what different conditions of salinity 
organisms at the bottom may be living. 
The bottom salinities recorded on our cruises for the mouth of the bay varied 
from about 26.00 to a little over 32.00 at area G, while in the region of Baltimore at 
area U they varied from about 6.00 to 17.00. These data, which are from the same 
cruises as those mentioned above, with the exception of July and September, 1916, | 
January, 1920, and January, 1922, when no data were obtained, show that the bottom 
salinity at area U on one occasion was as low as 6.54 (May cruise, 1920) and did not 
reach, at any time observed, a greater salinity than 17.38 (December cruise, 1920). At 
area G in the mouth the bottom salinity reached the lowest point observed, 25.77, 
during the May, 1920, cruise. While the maximum salinity observed was 32.57 in 
January, 1916, at area G. The range of bottom salinities, then, from head to mouth, 
may be very great — for example, 6.54 at TJ to 25.77 at G in May, 1920. 
It is of interest that the salinities at area U closely approach a point where the 
density is so low that, if continued for a long period of time, it is harmful to oysters 
(Moore, 1897). 
BOTTOM SALINITY FROM MOUTH TO HEAD 
A study of the data for the August, 1920, cruise shows that during this cruise 
the range of bottom salinities was from 31.74 (area G) at the mouth to 15.21 (area U ), 
as compared with 28.94 (area E) at the mouth to 4.75 (area U ) at the head for surface 
salinity during the same cruise. As in the case of the surface salinities, the greatest 
decrease per unit of distance, if one leaves out of consideration the high salinities of 
deep holes, took place between E, F, G, and D, C, B, A. At the mouth of the Potomac 
River, J, I, K to N, M, N', the decrease was quite marked; but in the long stretches 
from the mouth of the Potomac River north to Y, Z, and south to D, C, B, A changes 
per unit of distance were small, a condition which holds true for the surface salinity. 
An examination of the data for the rest of the cruises shows in general similar rela- 
tive amounts of decrease in bottom salinities per unit of distance for the regions just 
mentioned. 
An interesting exception to the gradual decrease in bottom salinity from the 
mouth to the head of the bay is seen at T, V, and Z. These areas, which lie on the 
west side of the bay from Governors Run to the mouth of the Magothy River, have 
fairly similar depths — for example, 9.15 meters at T, 10 meters at V, and 12.81 meters 
s More accurately on the north side, since this line runs about north and south. 
6 Only cruises for which there were sufficient surface salinity determinations are included in the counts. 
