PLANKTON OF THE GULF OF MAINE 97 



tive than we have previously found them at that season, thanks to the abundance 

 of large Calanus, with volumes of plankton per square meter for six stations along 

 the shore from Cape Ann to southern Cape Cod (July 19, 1922) ranging from 135 

 to 250 cubic centimeters (average 208 cubic centimeters) , and it was then that we 

 made the exceptionally rich horizontal net haul already mentioned (p. 96). 



Notes on the yearly numerical fluctuations in the local stock of the commoner 

 copepods will be found under the discussions of the several species. 



PLANKTON AS FOOD FOR WHALES AND FISHES 



We might, figuratively, conceive of the swimming and floating life of the sea 

 as a pyramid, with the microscopic plants as its base and the large sharks and whales 

 as its apex, the latter few in numbers but each enormously destructive of the smaller 

 organisms on which it preys. The general thesis that the smaller plankton, 

 animal and vegetable, is practically the sole food supply for young marine fishes no 

 longer requires further proof or argument. It likewise so serves for many species of 

 fish when adult, especially for the schooling fishes, such as herrings, menhaden, 

 mackerel, shad, and the like. The large adult gadoids, too, feed on plankton to 

 a greater extent than is generally appreciated. The great basking shark (Cetorhinus 

 maximus), which is still an occasional visitor to the gulf, is exclusively a plankton 

 feeder throughout its life, and most of the northern whalebone whales have long 

 been known to subsist largely on the smaller pelagic animals — several of them 

 exclusively so — a fact widely heralded in zoological textbooks. 



The literature dealing with the dependence of the larger marine animals on the 

 plankton has grown to formidable dimensions in the last half century, but very few 

 first-hand observations have yet been made on the relationships between fish and 

 plankton in the Gulf of Maine. So far as these go, however, they show that what 

 is true of north European seas in this respect applies equally to American waters, 

 as, indeed, might have been prophesied, allowing for the differences between the 

 composition of the planktonic communities of the two sides of the north Atlantic 

 Ocean. 



In the Gulf of Maine the groups of Crustacea that are of chief importance in 

 the diets of adult fishes and whales are the copepods and the euphausiids. Exami- 

 nation of stomach contents at European whaling stations has proved that instead 

 of subsisting indiscriminately on all sorts of plankton, large and small (as has some- 

 times been taken for granted) , or on pteropods (as the Arctic right whale often does) , 

 the planktonic part of the diet of the other species of whalebone whales common in 

 boreal seas consists almost exclusively of these two groups of Crustacea. While 

 there is ample ground for the choice of a crustacean rather than a molluscan diet in 

 the greater abundance of the former than of the latter on both sides of the north 

 Atlantic, it is possible that the whales in question may voluntarily prefer the harder 

 and more oily shrimps and copepods. 



The finback (Balxnoptera physalus Linne), commonest whale in the Gulf of 

 Maine to-day, eats a mixed diet of plankton and fish, devouring the latter, particu- 

 larly the herring, in great numbers, but probably depending more on the smaller 

 pelagic animals in the long run. A considerable number of finback stomachs have 



