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 journey ings 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 (. PollacMus 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 larvae 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 
