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 



' Compare stations 20044 to 20047 with stations 20127 to 20129, table, p. 299. 



