FISHES OF THE GULF OF MAINE 



419 



even in the Gulf of Maine large cod shift their range in depth with the seasons, coming 

 up into shoal water in autumn and winter as the temperature cools and sinking 

 deeper again in spring when the surface warms. 



Breeding migrations. — With the iirst ripening of the sexual products the feeding 

 and thermal migrations are annually interrupted by concentration on certain rather 

 definite spawning grounds, which for the larger fish involves a journey inshore or 

 to the shoaler part of the banks, and the breeding and thermal migrations are 

 combined in the case of those cod that winter west of Nantucket. 



Tagging experiments.^ — It is not known whether individual cod return year 

 after year to spawn on any particular ground or whether they may visit one region 

 in one season and another the next, nor has any attempt been made to trace the lines 

 of dispersal which they follow in the northern parts of the Gulf of Maine when they 

 are spent and recommence feeding. Apparently, however, tagged fish released at 



NUMBER OF FISH RECOYtRED NUMBER. OF FISH RICOVERID 



EA5T0F WOODS HOLE WEST OF WOODS HOLt 



2 4 6 8 10 12 14 16 18 2 4 6 8 10 12 14 16 18 



Fig. 211.— Numbers of tagged cod released at Woods Hole in 1898-1901 that were subsequently 

 recovered east and west of that point in different months 



Woods Hole after they had spawned (4,000 of them were liberated from December 

 to February of three successive years ^* and 4 per cent were recovered) , moved west 

 at first, for a number were retaken along the southern shores of New England and of 

 New York during December and January, while half a dozen were reported from 

 New Jersey, but not one east of Woods Hole until March 27. In April and May, 

 however, tagged fish were reported east of Woods Hole as well as west, and it was 

 during these two months that most of the recoveries were made, chiefly off Rhode 

 Island and New York and on Nantucket Shoals. While reports were received from 

 the latter ground and from off Cape Cod at intervals until September, June 10 was 

 the latest date west of Woods Hole. Unfortunately the tagged fish were all more or 

 less emaciated as the result of a stay of some weeks in the pool followed by artificial 



" Many experiments of this sort have been made in European waters. 

 " Smith (1902) gives a full account 



