418 BULLETIN OF THE BUREAU OF FISHERIES 



The general opinion is that the "school" fish, which compose the greater part 

 of the local stock of cod, are constantly on the move in loose groups, feeding along 

 over the bottom of their chosen bank and constantly moving on as they exhaust 

 the richest food. Though cod can hardly be described as "schooling" in the 

 same sense as herring or mackerel school, these armies of fish often hold together 

 so closely that it is common enough for one-half of a line trawl to come in loaded 

 with cod with the other half empty. It is these "school" fish which most often 

 prey upon fish and squid, though, like all cod, they feed chiefly on shellfish. They 

 run slenderer and lighter colored than the "grovmd" cod, with smaller heads, but 

 in all probability such differences are but temporary, reflecting the surroundings 

 of the individual fish and its mode of life at the time. A cod that is a "ground" 

 fish this month may start on its travels next, turning brighter and becoming more 

 shapely as it goes, either through a change of diet, the change of surroundings, or 

 more active exercise. 



Fishermen have known from time immemorial that bodies of cod undertake 

 extensive journeys with no apparent cause, suddenly deserting grounds where 

 they were plentiful to appear on other banks often far distant, and it is probable 

 (but not yet proven) that some interchange takes place from one bank to 

 another and between the offshore and inshore grounds. Furthermore, cod may 

 flee a given locality if too much harrassed by the spiny dogfish (p. 48), and no doubt 

 other enemies as well drive them at times, while the oft quoted discovery of hooks of 

 a kind used by the French fishermen on the Grand Banks of Newfoundland ^ in 

 cod caught in Ipswich Bay near Cape Ann is proof that at times they undertake 

 much more extensive migrations and perhaps do so oftener than is suspected, though 

 by what impulse they are driven is not known. 



When cod are on their travels they often desert the bottom for the mid-depths 

 (a fact proven by the level at which they are caught in nets), and netted fish are so 

 often empty while those caught on hook and line are full of food that they are 

 popularly (and perhaps rightly) believed to fast while on a journey. It is, we believe, 

 indisputable that cod usually congregate in denser bodies when traveling than when 

 feeding, bodies running very even in size, color, and shape, suggesting that they may 

 preserve their identitj^ for long periods but are mixed as to sex, sometimes males 

 and sometimes females predominating. 



Thermal migrations. — In the extreme northern and southern fringes of its geo- 

 graphic range the cod carries out regular seasonal migrations ; that is, it is "migratory" 

 in the common understanding of the term. Thus it is only in summer and early 

 autumn that they visit the waters of the polar current along the eastern coast of 

 Labrador, withdrawing again to the south or to deep water for the winter and spring. 

 On the other hand they appear only as autumn, winter, and early spring visitors 

 along the coasts of southern New England, New York, «,nd New Jersey, though in 

 numbers sufficient to support a lucrative fishery (the annual catch of cod between 

 .Nantucket and New Jersey may reach 2,000,000 pounds). Between these 

 extremes — that is, from the Grand Banks to Cape Cod — cod are resident to the 

 extent that they are to be found in one locahty or another the year round, but 



" Earll (1880) and Kendall (1898, p. 178) give instances of this. 



