PLANKTON OF THE GULF OF MAINE 
215 
Evidently the numbers of C. Tiyperboreus 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 15 for July, August, September, or October, while none at all 
have been detected at most of the midsummer and autumn stations. The fact 
that C. Tiyperboreus 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 80 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. Tiyperboreus 
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 in 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 — 0 . Tiyperboreus 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. Tiyperboreus 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. Tiyperboreus 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, 
11 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. 
IS Maximum for summer, 2,700 per square meter off Mount Desert Rock, Aug. 13, 1913, station 10100. 
