368 
BULLETIN OF THE BUREAU OF FISHERIES 
6. The surface salinity records for the mouth of the bay show a variation from 
approximately 19.00 to 30.00 per mille and for area U near the head of the bay from 
approximately 3.00 to 12.00 per mille. The more saline water was found as a rule 
along the eastern side. 
7. The bottom salinity records for the mouth of the bay show a variation from 
approximately 26.00 to 32.00 per mille and for area U, near the head of the bay, from 
approximately 6.00 to 17.00 per mille. The more saline bottom water was found on 
the eastern side of the bay except near the mouth of the Potomac River, where the 
deep channel approaches the western side. 
8. A sharp increase in salinity somewhere between the surface and 20 meters is 
quite marked in certain regions during the summer and autumn. Such a condition 
is found especially along the deep-water channel, sometimes at the mouths of rivers, 
and usually at the mouth of the bay. At times during the winter and spring months 
this condition is not so evident. 
9. Sometimes, especially during the early part of the year, when large quan- 
tities of fresh water enter the bay and when there is a greater tendency toward 
instability, the water approaches a homohaline condition from surface to bottom. 
10. While water samples could not be collected simultaneously at the various 
areas visited during a cruise, the salinity values obtained point strongly toward the 
conclusion that the salinity of the bay as a whole decreases markedly in the early part 
of the year, that it increases gradually during the middle of the year, and that it 
reaches a maximum toward the latter part of the year. 
11. The same data, as might be expected, show a decreasing range of salinity 
va'ues with few exceptions from the mouth to the head for each depth investigated. 
12. The surface temperature at the mouth of the bay varies at least from 4° C. 
to 27° C. (area G) and near the head of the bay (area U) from 0.0° C. to 25° C. We 
have not been able to formulate any definite rule for the distribution of surface tem- 
perature with reference to the east and west sides of the bay. 
13. The bottom temperature at the mouth of the bay varies at least from 
3.6° C. to 21.0° C. (area G ) and near the head from at least 0.9° C. to 24.4° C. (area 
U). During the summer cruises the coldest bottom water was found along the deep- 
water channel, while during the winter cruises this channel contained the warmest 
water. 
14. A discontinuity in range of temperatures from the surface to the bottom 
occurs, especially during the warmer months of the year, when the water is more 
stable. This discontinuity often corresponds closely in depth to that of the discon- 
tinuity of the salinity. 
15. The temperature data for the winter cruises indicate that there was a 
decreasing range from the mouth to the head and that this was partly due to the 
entrance of the warmer water from the ocean ; during the spring cruises the tempera- 
ture data showed that these relations were not constant; during the summer cruises 
the deep-water temperatures showed an increasing range from the mouth to the head, 
and this undoubtedly was partly due to the entrance of ocean water, which is of a 
lower temperature than that of the bay water at this season; finally, the temperatures 
of the autumnal cruises indicate that, at that time, the summer conditions were 
changing to those of the winter. 
16. Practically a 1 of the marine planktonic diatoms found in Chesapeake Bay 
during the year 1916 belonged to the neritic temperate group, only one neritic arctic 
