PLANKTON OF THE GULF OF MAINE 215 



Evidently the numbers of C. hyperboreus existing in the gulf increase considerably 

 from February to May and then decrease during June, 14 and later in the summer 

 the species becomes so scarce that we have never found as many as 3,000 per square 

 meter at any station I5 for July, August, September, or October, while none at all 

 have been detected at most of the midsummer and autumn stations. The fact 

 that ft hyperboreus has been detected at only about 10 per cent of the towing stations 

 for July and August, notwithstanding its wide distribution at that season, con- 

 trasting with its presence at SO to 100 per cent of the stations during March, April, 

 May, and June (p. 212), is further evidence of its scarcity in the Gulf of Maine in 

 summer. In 1915 it occurred at 10 per cent of the September stations and at one 

 out of eleven stations east and north of Nantucket in October, while in December, 

 1920, and January, 1921, Dr. C. B. Wilson detected it at about one-third of the 

 stations. 



The regional distribution of the richer and scantier catches of C. hyperboreus 

 proves interesting from the standpoint of the source of the local stock, whether 

 endemic or immigrant. When the stations are plotted, where appreciably more 

 than the average number per square meter for the respective months were taken, 

 (fig. 69), it appears that during the season of maximum abundance for the species 

 (March to June) it is usually most plentiful iu three distinct localities — (1) in the 

 Massachusetts Bay region and thence out to the western basin; (2) in the eastern 

 side of the gulf from the northern channel (but not on Browns Bank) westward over 

 the neighboring basin; and (3) along the southeast face of Georges Bank. In all 

 other parts of the gulf, including the waters intervening between these "rich" 

 centers — that is, all along the coasts of Maine, in the northeastern corner off the Bay 

 of Fundy, in the central and southern parts of the basin, and over Georges and 

 Browns Banks — ft hyperboreus has been uniformly much scarcer. Unfortunately 

 the stages in development of the specimens taken in the vertical hauls, on which this 

 chart is based, have not yet been determined; but such a distribution, coupled with 

 the seasonal increase in the numbers of C. hyperboreus during the spring, would be 

 presumptive evidence that the western center is a region of local production, drawing 

 little from immigration but contributing to the stock in other parts of the gulf. 



If such be actually the case, this would be by far the most southerly spawning 

 ground for this species. Until Willey's (1919) account of the copepods of the 

 Canadian fisheries expedition appeared, such a suggestion might have seemed highly 

 improbable, C. hyperboreus having previously been known to breed only in the polar 

 sea; but his discovery of young stages, besides adult females (but no adult males), 

 in the gatherings at many localities in the Gulf of St. Lawrence, southeast of Nova 

 Scotia, and along the continental shelf westward nearly to the longitude of Cape 

 Sable, proved that the regular breeding range of this copepod extends much farther 

 south along the American coast than it does off Europe. Willey has more recently 

 reported adult males — previously known only from the far north — as well as adult 

 females and younger stages at the mouth of the St. Croix River near St. Andrews, 



» This statement is justified by the fact that the cruises for April, May, and June have covered the parts of the gulf most pro- 

 lific in this species. 



11 Maiimum for summer, 2,700 per square meter off Mount Desert Rock, Aug. 13, 1913, station 10100. 



