168 BULLETIN OF THE BUREAU OF FISHERIES 



commercial fishes depends very largely on the stock of copepods. As Dr. C. B. 

 Wilson writes, it is not too much to say that "their presence and abundance 

 count as much for the higher animal life in the ocean as does that of nitrates in the 

 soil or carbon dioxide in the air for plant life upon the land," for they are the chief 

 intermediary through which the elemental foodstuffs elaborated by the marine 

 plants on which the copepods feed are made available for the support of the larger 

 marine animals that feed on them. 



Copepods are the only animal group that has been systematically counted in the 

 catches of the vertical nets in the Gulf of Maine; and while the numerical calculations 

 include so many indeterminate sources of error that they can be taken only in a 

 general way, they have proved undeniably instructive in tracing the seasonal perio- 

 dicity and relative regional abundance of several of the more common species. I 

 must emphasize, however, that the counts given are only a rough indication of the 

 relative abundance or scarcity of the several species, and that the "probable error" 

 (unknown) may amount to as much as 80 to 100 per cent in extreme cases. (For a 

 discussion of the allowance that must be made on this account see Johnstone, Scott, 

 and Chadwick, 1924, p. 180.) 



For the group as a whole the numbers present per square meter have varied 

 from next to none at occasional stations in the coastwise zone during the early spring, 

 when diatoms are flowering and copepods are scarcest (p. 39), to upwards of 500,000 

 in May, when Calanus finmarchicus is swarming (e. g., station 10266, May 4, 1915). 

 Copepods are at their lowest ebb in the gulf in February and March, when the maxi- 

 mum per square meter at any station within the edge of the continent in 1920 was 

 37,500 (station 20049, in the western basin), the minimum 55, in the inner part of 

 Massachusetts Bay, and the average about 6,600. Generally speaking, at this season 

 there are more copepods under any given area of the sea surface in the deeper parts 

 of the gulf than in the shoal, the numbers caught being roughly proportional to the 

 amount of water strained by the net in its journey from the bottom up to the surface. 

 Thanks to a swarm of Calanus (p. 189), there were more copepods outside the south 

 eastern edge of Georges Bank than anywhere within the gulf. 



In April, 1920, the average within the continental waters of the gulf was about 

 twice as large (13,300) as it had been in March, the maximum more than three times 

 (130,000 in the northern channel), and the minimum had risen from 55 to 900. 



In another chapter (p. 41) I have commented on the tremendous augmentation 

 of copepods which takes place in May and for which the vernal wave of reproduction 

 of Calanus finmarchicus is chiefly responsible. In 1920 this was hardly under way 

 by the middle of the month, but in 1915 it had raised the average number of copepods 

 over the inner parts of the gulf to upwards of 140,000 by the 4th to the 14th (stations 

 10266 to 10278), with maxima of 511,000 off Cape Ann on the 4th and 411,500 in the 

 eastern side of the basin on the 6 th. 



Fewer copepods were taken in June, the average being only about 23,000 per 

 square meter. The fact that the vernal reproductive activity commences later 

 in the northeastern and eastern shallows of the gulf, where most of the June stations 

 were located, than in its western side is chiefly responsible for this apparent shrinkage; 

 but with only about one-seventh as many copepods in the eastern basin on June 19, 



