96 
BULLETIN OF THE BUREAU OF FISHERIES 
in July, 1916 (station 10342, at least 4.5 cubic centimeters per cubic meter); but 
occasionally it is much more dense than this at one level or other, the volumes just 
listed being the minima possible. For example, a horizontal haul of 15 minutes’ 
duration at 40 meters depth, with a net 1 meter in diameter, off Cape Cod on July 
22, 1916 (station 10344), yielded over 6 liters, mostly copepods, which is equivalent 
to about 12 cubic centimeters per cubic meter for the water fished through (the tow 
covered about one-third of a mile) . In fact, it was the richest tow-net catch we have 
ever made in the gulf, although the vertical haul indicated only about 2.8 cubic 
centimeters of plankton per cubic meter. 
ANNUAL VARIATIONS IN ABUNDANCE 
Annual variations in the amount of zooplankton living in the waters of the 
gulf will mirror the long-time fluctuations in its physical state — may, indeed, be 
the best clue to such — and exert an important influence on the growth, local repro- 
duction, and distribution of the adults of such important plankton-feeding fishes 
as herring, mackerel, and pollock. 
It is certain that considerable fluctuations of this sort in the plankton do take 
place from year to year, as illustrated by the following table of the volumes per 
square meter of sea surface for corresponding localities in the summers of 1913-14 
and the first week of September, 1915. 45 
Locality 
Stations 
Plankton, in cubic centimeters 
per square meter 
1912 
1913 
1914 
1915 
1912 
1913 
1914 
1915 
' 10002 
10087 
10253 
10306 
250 
180 
60 
110 
‘ 19007 
10089 
10254 
10307 
65 
80 
200 
165 
10090 
10255 
120 
70 
10028 
10092 
10249 
10309 
30 
160 
105 
425 
10095 
10244 
10311 
60 
15 
45 
10031 
10096 
10245 
10315 
30 
120 
60 
50 
10036 
10246 
30 
200 
Of! Petit Manan Island 
10033 
10098 
10247 
10316 
2 25 
70 
10 
12.5 
10100 
10248 
220 
100 
10033 
10101 
10250 
2 10318 
20 
100 
350 
25 
74 
123 
117 
117 
1 July hauls. 2 From horizontal hauls. 
1 A few miles west of the corresponding stations, 1912 to 1914. 
According to these measurements the volume of the plankton was greater in 
1913 than in 1914 at all but two stations. As between 1913 and 1915, however, 
one year was the richer at some, the other at other localities. However, since the 
average is practically the same (or at least did not differ as widely as the probable 
error) for the three years, there was apparently no important general change in the 
amount of plankton existent in the gulf from 1913 to 1915, though both these years 
were apparently decidedly more productive, on the whole, than was 1912 during 
the corresponding months (Bigelow, 1915, p. 337). During the summer of 1916 
(a year of low temperatures) the waters off Massachusetts Bay proved more produc- 
ts Although different types of nets were used during these years, the results, reduced to the common standard, will allow 
rough and ready comparison. 
