6 
BULLETIN OF THE BUREAU OF FISHERIES 
The great drop in the number of tagged cod that has been reported recaptured 
after more than a year, particularly in those experiments recorded by Boreley (1909) 
and Strubberg (1916, 1922), was due in part to the intensity of the local fishing which 
removed so many of the marked fish within the first year and in part to the large 
number of fish that lost their tags. Graham (1929b, p. 23) points out that the per- 
centage of marked fish recaptured in a year has frequently been used as a minimum 
value in calculating the percentage of the stock taken by the fishermen, and that his 
tank experiments make it apparent that this value should be increased to account for 
the loss of tags. As we have found in our cod-tagging experiments off the New 
England coast (1923-1929) that the loss of tags the first year is very great, it is 
evident that the percentage of tags returned is not a good criterion in estimating at 
what rate the fishery depletes a stock of fish, other than that the percentage of tags 
returned must be considerably less than the actual percentage of the stock of fish 
caught. Most of the cod tagged in the European experiments were less than 60 
centimeters long, hence it would not seem that death due to old age was an important 
factor in the small number of returns subsequent to the first year after marking. 
The results of all these cod-tagging experiments agree in one important respect, 
namely, that most of the fish remain more or less stationary for long periods and 
that each region— the North Sea, coast of Norway, the Faroes, and Iceland — has its 
own stock of fish. In a few cases a migration was indicated, as along the coast of 
Norway and from the north to the south coast of Iceland. 
Certainly the thousands of cod that have been tagged in European waters during 
the past 25 years, and the great percentage of recaptures returned by the intensive 
fishing which prevailed in all the tagging areas, would have revealed an intermigration 
if it had occurred between such localities as the North Sea, the Faroes, and Iceland. 
Very likely deep water prevents an intermingling of these various stocks of fish, 
although Jensen (1905, p. 11) found cod otoliths ( Gadus callarias ) at the bottom of the 
polar deep off the Faroes and comments on the fact that both Hjort and Schmidt 
report cod in the upper 60 fathoms in that region, taken with hook and line and with 
drift nets, over depths of 350 to 1,000 fathoms. Furthermore, the very fact that cod 
in the North Sea and elsewhere did not migrate soon after being tagged, but remained 
in the same general locality for several years, indicates that, taken as a whole, they 
are not a roving fish even though upon occasion some schools of fish may make 
extensive migrations. 
The causes of migrations such as those of the Icelandic cod are not so evident, 
although it has been suggested that a low temperature and the urge to spawn caused 
these fish to seek the southern coast of the island. The fact that cod up to about 4 
years of age remain off northern Iceland in the 0° C. water of winter and spring when 
they could so easily migrate into warmer water is of interest. There are instances in 
American waters, too, where cod are caught in very cold water as, for example, in the 
Gulf of St. Lawrence and on the Grand Banks where the bottom temperature is 
frequently below 0° C. 
REVIEW OF COD TAGGING OFF THE NEW ENGLAND COAST 
The only previous cod-tagging experiment on the American coast was carried 
out during the years 1897-1901 by the United States Fish Commission. (Smith, 
1902.) These cod were caught primarily for the purpose of securing spawn and were 
retained in a large cistern at Woods Hole, Mass., until they were spent. All were 
caught on Nantucket Shoals during late October and November with hook and line 
