200 
BULLETIN OF THE BUREAU OF FISHERIES 
Among 246 hauls, vertical and horizontal, for which the proportionate rep- 
resentation of different copepod species has been determined, 51 have contained 
90 per cent or more of C. finmarchicus. At 12 of our 42 tow-net stations for July 
and August, 1912, this was the only copepod detected by Doctor Esterly in the 
subsurface hauls. Its dominating role in the copepod community of the gulf may be 
further emphasized by the statements that it has been an unusual event for any other 
species to form as much as 50 per cent of the catch, and that we have never found 
as many as 50,000 of any other copepod per square meter, though there are often 
upward of 100,000 Calanus. 
The frequent dominance by C. finmarchicus, especially in spring and early 
summer, not only over other copepods but of the entire community of planktonic 
animals, is commented on in an earlier chapter (p. 37). If the seasons of 1920 and 
1921 can be taken as representative, C. finmarchicus is at its lowest ebb (compared 
with other copepods, as well as absolutely) during January and February, when 
it constituted 30 to 90 per cent (average about 55 per cent for the two months) of 
the copepods caught in horizontal and vertical hauls in the inner parts of the gulf 
(tables, pp. 299 and 304), but only 2 to 10 per cent over the western end of Georges 
Bank or outside the continental edge to the southward. The average percentages 
for March (58 per cent) and April, 1920 (57 per cent), were about equal, but 
experience in 1915, 1916, and 1920 proves that the percentage of Calanus among 
the total copepods increases notably as the spring advances, consequent on the 
active vernal multiplication of this species (p. 194), which no other local copepod 
rivals. In 1920 the relative augmentation of C. finmarchicus far outstripped the 
general augmentation of the copepod community as a whole 1 in the southwestern part 
of the gulf and on the western portion of Georges Bank. The percentage of Calanus 
in the vertical hauls at the May stations for the two years combined averaged about 
80 per cent for the more prolific parts of the gulf. 
Direct comparison can not be made between the percentages for May and for 
June (average 56 per cent), because most of the stations for the latter month were 
located in the northern corner of the gulf, where we have not towed in May. Con- 
sequently, the difference may be a regional phenomenon, not seasonal. 
The vertical hauls for August, 1913—14 in number — give an extreme range of 
from 87 per cent to 12 per cent Calanus, averaging 50 per cent, and 4 August hauls 
for 1915 average 46 per cent Calanus, suggesting that this species is proportionately 
less dominant in the general copepod population of the gulf in late summer than 
in spring. Forty-five horizontal hauls at various depths generally distributed over 
the gulf, including Georges Bank and out to the continental shelf, for July and 
August, 1914, averaged 71 per cent Calanus, with 100 per cent on several occasions, 
in both surface and deep hauls — that is, about the same percentage that resulted 
from the vertical hauls for May, 1920 (table, p. 302), and only slightly less than for 
that month in 1915 (table, p. 297). It is therefore doubtful whether any decided 
diminution in the percentage of Calanus, relative to other copepods, is a regular 
phase in its annual cycle in the gulf during the period June to August, though there 
may be a considerable variation in the percentage of Calanus from summer to 
1 Compare stations 20044 to 20047 with stations 20127 to 20129, table, p. 299. 
