PLANKTON OF THE GULF OF MAINE 127 



Georges Bank as the season progresses, for we did not find it at any station there or 

 along the continental slope abreast the gulf in July of 1913, 1914, or 1916. 



We have never found Clione assuming any faunal prominence in the open waters 

 of the Gulf of Maine, where it is usually represented by occasional specimens only 

 among the mass of other plankton brought in by the nets. For example, in Febru- 

 ary, March, and April, 1920, all our hauls combined yielded not over 175 specimens 

 of Clione, although it occurred at some 30 stations, whereas various other animals 

 were captured in thousands — even millions in the case of the commoner copepods. 

 Wood (1S69, p. 185), it is true, found Clione so abundant in Portland harbor in May, 

 1S68, that "the water appeared to be alive with them," but our experience ever 

 since 1912 has been so consistent in this respect that I can only look on such local 

 swarms of Clione as altogether exceptional for the Gulf of Maine, although this 

 pteropod regularly appears in vast shoals in more northern seas. 



It is still uncertain to what extent Clione is endemic in the Gulf of Maine. 

 There is every reason to suppose that it immigrates more or less regularly into the 

 gulf around Cape Sable via the Nova Scotian current, as do the various Arctic 

 organisms, because it is far more numerous off the east coasts of Newfoundland and 

 Labrador — where I found it swarming among the floe ice in the summer of 1900 — 

 about the Grand Banks of Newfoundland, and in the Arctic seas as a whole, than we 

 have ever found it of late years in the Gulf of Maine or farther south. However, 

 as I have elsewhere emphasized, in reality the local presence of Clione is not the 

 sure index to Arctic currents many have supposed (Bigelow, 1917, p. 301, and 

 1922, p. 174), for it is as abundant in Atlantic as in Arctic waters around Iceland 

 (Damas and Koefoed, 1907; Paulsen, 1910); and while Clione grows to a larger size 

 in the latter than in the former, there is no reason to doubt, from their evidence, 

 that it breeds successfully in both. Many authors have quoted its abundance south 

 of Ireland, to which Massy (1909) called attention, and where there is no reason to 

 credit it with an Arctic origin. According to Dr. A. G. Huntsman (in Bigelow, 1922, 

 p. 135), its larvae are found over the whole region from the Gulf of Maine to the Gulf 

 of St. Lawrence and the Newfoundland Banks, at sea but not in estuaries. 



Like many other animals, Clione decreases in numbers toward the boundary 

 (in this case the southern) of its range, but it is probably impossible to draw any 

 sharp line beyond which it can not maintain itself. No doubt as we pass from north 

 to south it becomes more and more dependent on accessions of fresh blood from the 

 north for the maintenance of the local stock, but in favorable seasons it may be 

 expected to reproduce itself in unwonted numbers far beyond its normal zone of 

 abundance. Probably the Portland swarm just mentioned resulted from an unusu- 

 ally successful wave of local reproduction; and the generality of its distribution over 

 the gulf suggests that more or less Clione are produced there yearly, though probably 

 immigration via the Nova Scotian current is the more important source of supply. 

 On the whole, I see no reason to alter the view, earlier stated, that it probably 

 rarely succeeds in breeding south of Cape Cod. Even in the Gulf of Maine 

 Clione can reproduce itself in abundance only on the occasions when hydro- 

 graphic conditions conspire in its favor, conditions occurring so rarely that only 

 the one instance of this is known. I must caution the reader that very few 

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