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BULLETIN OF THE BUREAU OF FISHERIES 
Finally, it may be mentioned that so far as the time of the occurrence (autumn 
and winter) of a strong tendency toward an incoming current in the lower layers is 
concerned, it would be permissible to relate that phenomenon to the influence of 
the North Equatorial Stream and the Atlantic gyral (Gulf Stream eddy) of which 
it is a part. It is known (Johnstone, 1923) that the axis of this stream or drift and 
also the rest of the Atlantic gyral shifts in a northerly direction during the summer, 
reaching its northermost position in the autumn; and that in such regions as the 
North Sea, Irish Sea, and Baltic Sea the culminating effect of this moving water occurs 
in March or in some regions later. Chesapeake Bay might be expected to show the 
effect of this movement of saline water during the autumn and winter, but while the 
data on salinity, temperature, current velocity,, and current direction show that 
there is at times an unusual inflow of saline water into the bay during the autumn 
and winter, there is no conclusive evidence to support the theory that this condition is 
brought about by the northerly shift of the Atlantic Stream gyral alone or even in part. 
TEMPERATURE OF WATER 
It is well known that certain organisms are adapted to one range of temperatures 
and that others flourish under a different range. Also, it is known that there are some 
which are very hardy, being able to live between widely separated extremes, and 
that others are sensitive and can exist only within a small range of temperatures. 
Such a dependence on temperature must necessarily be an important factor in deter- 
mining the latitudinal, seasonal, and vertical distribution of aquatic animals and 
plants. Furthermore, the degree of temperature undoubtedly is often an important 
factor in regulating the rate of reproduction, and extreme temperatures may at times 
cause great mortality. Finally, it is believed that temperature is a factor which has 
an influence on the migration of some fishes. For these reasons water temperature 
data have been recorded. A discussion of the data follows. 
SURFACE TEMPERATURE AT MOUTH AND HEAD 
The temperature data for the surface water collected at the mouth of Chesapeake 
Bay on the various cruises showed a variation from about 4° C. to 27° C. at area G, 
while at the head (area U) near Baltimore temperatures ranging from about 0.0° C. 
to 25° C. were found. The data for January, March, April, June, July, September, 
1916; August, October, December, 1920; January, March-April, May-June, 1921 ; and 
January, March, 1922, show a maximum surface temperature of 27° C. at area G in 
August, 1920, and only on one cruise a temperature as low as 3.7° C. (at area G in 
March, 1916). 
At area U, near Baltimore, the highest surface-water temperature recorded on our 
cruises was in August, 1920, 24.8° C., and the lowest, 0.3° C. in January, 1921. The 
maximum surface temperature seems to have been about the same for the mouth 
and the head ; but the minimum was lower at the head than at the mouth, due undoubt- 
edly to the presence of ice floes and to slightly lower air temperatures during the 
winter. 
Temperature data were collected also during January, March, May, and July, 
1920. The thermometers used during this period were tested for accuracy and the 
necessary corrections were determined; but since they were not of the reversing type, 
and hence not suitable for work at depths, it is considered best to disregard the results. 
However, the surface readings for the latter part of the first week in March, 1920, 
