76 BULLETIN OF THE BUREAU OF FISHERIES 



because no important spawning is known for this fish south of the Massachusetts 

 Bay region (Bigelow and Welsh, 1925). 



There is no evidence that the larval stages of the cod or flatfish families acquire 

 a contranatant (that is, up-current swimming) habit, as the herring does. Conse- 

 quently the extent of their involuntary journeyings depends on the duration of the 

 pelagic stage as much as on the velocity of the drift with which they travel. Very 

 little information has been gathered on this in the Gulf of Maine, but in north 

 European seas both the American pollock (PoUachius virens) and the haddock are 

 pelagic for about three months; most of the cod hatched in the Gulf of Maine prob- 

 ably are so for at least two months, if not longer, before they take to the bottom. 

 So far as the elapsed time goes, experience with drift bottles suggests that this may 

 be long enough for some of them to make the entire round of the gulf — that is, from 

 off Mount Desert or Penobscot Bay around to the Bay of Fundy — but whether any 

 of them actually do so is not known. The extent of the actual drifts of different 

 species would be governed largely by the levels in the water at which the larvas live. 



Schmidt's (1909) classic and oft-quoted study of the distribution of cod and 

 American pollock (Pollachius virens) eggs and fry around Iceland illustrates how 

 far apart the fry of different species, hatched from eggs spawned in the same general 

 regions, may travel before abandoning their pelagic life, if living at different levels 

 and pelagic for different lengths of time. The two fishes in question spawn at the 

 same season (maximum egg production about April), and both of them mainly, if 

 not exclusively, off the southwest and south coasts of the island, while the fry of 

 both show a tendency to drift thence westward and northward. But while the 

 American pollock mostly descend to the bottom in practically the same waters where 

 spawned, either because their span of pelagic life is short or because living at such a 

 level that they drift slowly, the young cod generally travel right around the island 

 (a trip of something like 500 miles for many of them) , and the result is a scarcity of 

 the youngest bottom stages on the south and west but a great predominance of them 

 over those of the pollock off the northeast and east coasts. The Icelandic haddock 

 likewise perform; a similar involuntary migration, enduring from May until July. 



The great abundance of young pollock only a few inches long along the littoral 

 zone in the Gulf of Maine suggests that the involuntary drift of the pollock is also 

 shorter with us than is that of cod or haddock. Here, again, definite evidence, one 

 way or the other, is lacking for want of systematic towing during January and 

 February. 



Very few definite observations have been made on the depths at which the 

 various young fish live while pelagic in the Gulf of Maine, and it is not safe to assume 

 that these will be the same as in the northeastern Atlantic, the vertical distribution 

 of temperature and of salinity being different. It is probable that the young pollock 

 frequent the surface layers more than either cod or haddock (except for such of the 

 latter as live commensal with medusae), this being the case in European waters; 

 but the involuntary migrations of the Gulf of Maine pollock take place in winter 

 when the circulation of the gulf is believed to be at its minimum. Drift bottles 

 released during the period from January to March would be extremely instructive 

 in this connection. On the whole, the drifts of young cod may be expected to follow 



