416 BULLETIN OF THE BUREAU OF FISHERIES 



of diet the flesh of the greater shearwater ("hagdon") has long been considered 

 excellent cod bait. Objects as indigestible as pieces of wood and rope, fragments 

 of clothing, old boots, jewelry, and other odds and ends have repeatedly been found 

 in cod stomachs, and they often swallow stones, but probably for the sake of the 

 anemones, hydroids, etc., growing thereon, and not to take on ballast for a journey 

 as the old story has it. Although cod are so rapacious they fast so generally while 

 spawning that the stomachs of nearly all the ripe fish examined by Earll and recently 

 by Welsh were empty. 



It is not surprising that a fish as nearly omnivorous as the cod is caught on 

 various baits. Those most in use are clams (Mya arenaria), cockles (Lunatia), 

 herring (fresh, frozen, or salt), and squid. General experience suggests that there 

 is little to choose between the first two, while the razor clam (Ensis direchis) is 

 equally attractive though its employment is limited by the small supply; and tests 

 made in the Gulf of St. Lawrence 80 proved that fresh herring and fresh squid are 

 about as good as clams, but frozen or salt herring is less attractive. Other kinds 

 of fish are also used as cod bait in other parts of the world — capelin, especially 

 in more northern seas, and launce. 



Experiments performed on the cod in captivity, 81 combined with the general 

 experience of fishermen, suggest that it captures moving objects that may serve 

 as food by sight; but apparently cod, and for that matter other fish as well, can 

 see clearly only for a few feet, and their greediness in snapping up the naked meat 

 of clams, cockles, etc. (foods which they never find in that condition in nature), 

 and the fact that they bite as readily by night as by day, seems to us sufficient 

 evidence that they depend largely on smell. 



Enemies. — In the Gulf of Maine, where there are few large sharks or seals, 

 the spiny dogfish is the worst enemy of the adult cod, and that of young cod 

 fry is the pollock which infest our harbors. These small pollock are so fierce that 

 a single individual 7 to 8 inches long will disperse a school of hundreds of cod fry, 

 driving them to shelter among the weeds and rocks, while Earll remarks that in 

 the aquarium a cod so fears a pollock of equal size that it will invariably hide if 

 possible. 



Migrations. — It has long been known that cod carry out extensive migrations, 

 European (particularly Scandinavian) biologists having succeeded in tracing the 

 major outlines of these for north European seas, and while the movements of cod 

 are not well understood in North American waters enough evidence has been 

 accumulated to show that they fall into the same categories on the one side of the 

 North Atlantic as on the other. These are, first, the involuntary migrations 

 carried out by the larvje while they float near the surface at the mercy of ocean 

 currents, followed (after they take to bottom) by feeding migrations that cover 

 most of the wanderings of the immature fish as well as those of the adults between 

 successive breeding seasons, and which are intimately connected with the thermal 

 migrations (for it is in pursuit of food that cod may spread at one season to a region 



eo Knight. Contributions to Canadian Biology, 1906-1910 (1912), pp. 23-32. Ottawa. 



•' Bateson. Journal, Marine Biological Association of the United Kingdom, New Series, Vol. I, 1889-90, p. 241. Plymouth. 



