PLANKTON OF THE GULF OF MAINE 69 



abundance elsewhere (chiefly to the eastward and northward), connected with the gulf 

 by a continuous zone of occurrence, but all of them are regularly more abundant in 

 the particular temperatures, salinities, densities, etc., that characterize the Gulf of 

 Maine than immediately outside it, whether to the east or the west or offshore. 

 Indeed, such multitudes of several of these species (Calanus, especially) arc pro- 

 duced there that the small accessions which the gulf may receive from the north 

 must be far outnumbered by the emigrants that emerge from it to journey either 

 northward along the inner edge of the continental slope, on the one hand, or around 

 Cape Cod to the westward and southward over the outer part of the continental 

 shelf, on the other. It is probable that the boreal winter plankton of the coast 

 water south of New York draws more from this source than from local production. 



MIGRATIONS OF PELAGIC FISH EGGS AND LARWE 



One of the most interesting and economically important fields of study to which 

 our Gulf of Maine explorations are introductory is the involuntary migrations of 

 the early stages of fishes, with the effects of such journeyings on the fish population of 

 different parts of the gulf. 



Any information obtainable on this subject is instructive from the point of view 

 of the migration of the plankton within the gulf, because every buoyant fish egg 

 floats from spawning until hatching, wherever the current may carry it, rising or 

 falling vertically according to specific gravity of the water only, with the young 

 larvae equally at the mercy of tide and current until after the yolk sac is absorbed. 

 Even the older pelagic fry of most fishes are hardly less helpless, so far as voluntary 

 horizontal migration is concerned, until they attain considerable size (some species 

 become contranatant — that is, turn to swim against the current — at an early stage), 

 even though they are able and do swim up and down and thus exercise a choice of 

 level at which they live. 



Now the water of the open sea never being at rest (no area as large as the gulf 

 lacks some dominant movement, if not a definite current, in one direction or another), 

 it follows that only in the rarest instances does a fish hatched from a buoyant egg 

 ever grow large enough to descend to the bottom in the precise locality where the 

 egg that gave it birth was spawned. The drift during its pelagic life may be only a 

 few miles if spawning occurs in some bay or sound sheltered from the free circulation 

 of the sea by off-lying islands; it may, indeed, be almost nil in this case, should the 

 tidal currents in the two directions be of equal strength. Outside the outer head- 

 lands, however, the journeyings of floating fish eggs are, generally speaking, so 

 considerable that they are often measured better by degrees of latitude and longitude 

 than by miles. Such, to quote only a couple of the more striking and better known 

 examples, is the case with the cod eggs spawned south and west of Iceland, for most 

 of the fry resulting therefrom drift right around to the north and east coasts of the 

 island before they seek the bottom (Schmidt, 1909). Off Norway, too, cod eggs 

 and fry have long been known to carry out long journeys with the current (Damas 

 1909a; Hjort, 1914). Indeed, events of this sort are inevitable, given the indicated 

 factors of animals able to swim but weakly, caught up in the set of any current. 



