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BULLETIN OF THE BUREAU OF FISHERIES 



surface of the sea may be scattered sparsely through a great depth or concentrated 

 in a shoaler stratum, depending both on the depth of water at the station in question 

 and on whether they are more or less stratified or are evenly distributed from the 

 surface downward. 



In spring the latter state may be said to apply generally down to 175 meters; 

 and assuming that practically the whole catch (in the case of the deeper hauls) was 

 made above that level, as seems justified for the reasons outlined above (p. 24), 

 we arrive at an average of about 48 Calanus per cubic meter for March, 1920, and 

 69 for April, with extremes of 1 to 654 and 4 to 624, respectively, for these two months. 

 Thus it seems that a slight general increase took place from March to April, cor- 



Fig. 67. — Numbers of the copepod Calanus finmarchicus per cubic meter of water in May and June, 1915, as calculated 

 from the vertical hauls, assuming that all were living shoaler than 175 meters depth 



responding to the beginning of the vernal wave of reproduction of the species, but 

 irregularly from station to station and reversed at many stations, without apparent 

 correlation between the relative density of aggregation and the depth of water or 

 the locality in the gulf. 



As might be expected, the great increase in abundance of this copepod which 

 takes place in May is accompanied by a corresponding increase in the numbers 

 present per cubic meter to an average of about 500 for all the May and June stations 

 of 1915 and 1920 combined (fig. 67) — that is, to more than seven times the April 

 average — and with a well-defined cleavage into "rich" and "poor" regions. In the 

 western parts of the gulf and along a line toward Cape Sable Calanus then averaged 



