MIGRATIONS OP COD 
11 
Table 5.— The numbers of cod lagged each year from 1923 to 1929 off southern Massachusetts and to the 
westward, according to fishing grounds 
Locality 
1923 
1924 
1925 
1926 
1927 
1928 
1929 
Total 
2 
37 
39 
475 
26 
6 
507 
Nantucket Shoals: 
1C4 
184 
31 
1 
32 
4,881 
1,105 
1,028 
85 
1,932 
76 
769 
2, 949 
746 
105 
12, 487 
2, 358 
Between Round Shoal and Rose and Crown buoys 
388 
254 
139 
473 
1, 328 
553 
84 
2 , 050 
1,314 
1,319 
2, 140 
5 to 12 miles southeast of Round Shoal buoy __ 
796 
515 
3 
28 
75 
1, 173 
403 
43 
310 
926 
369 
45 
81 
793 
63 
7 
157 
1,020 
125 
92 
33 
166 
134 
300 
416 
468 
884 
7,605 
3, 105 
4, 043 
1, 606 
5,661 
1, 549 
1,170 
24,739 
SIGNIFICANCE OF A RECAPTURE RECORD 
The conclusions concerning the migrations of New England cod must neces- 
sarily be based largely upon the recapture records as furnished by fishermen and as 
obtained by the Bureau of Fisheries vessels Halcyon and Albatross II. Therefore, it 
is important to consider how much significance is to be attached to each record. 
The factors affecting the recovery of tagged cod which have an important bearing 
on this question may be classed as follows: (1) The death rate due to tagging and 
occurring soon thereafter; (2) deaths due to old age, enemies, disease, etc.; (3) the 
percentage of fish which lose their tags before recapture; (4) the intensity of fishing 
as affecting the tag returns; and (5) the percentage of recaptured fish which are not 
reported. The following discussion concerns chiefly those cod which were tagged on 
Nantucket Shoals. 
The death rate due to tagging and occurring soon thereafter.- — We have attempted 
to keep the loss of fish from this cause at a minimum by utilizing uninjured fish only. 
Although nearly every fish tagged appeared to be in good condition when returned 
to the water, nevertheless it is probable that a small number died from various causes 
attributable to the act of tagging. This loss may arbitrarily be set at 5 per cent. 
Deaths due to old age, disease, enemies, etc. — Deaths due to old age doubtless occur. 
It seems that cod of 48 inches or more in length and upward of 10 years of age lack 
the vitality of smaller and younger fish, for they die sooner when taken from the 
water. Fewer of them survive the ordeal of capture and of tagging when returned 
to the water. 6 But the great majority of the cod caught for tagging purposes have 
been considerably below this size, hence might be expected to live at least five years 
longer before old age and consequent weakness would become an important factor in 
their death rate. 
Little is known concerning the death rate due to the attacks of enemies other 
than man among adult or nearly adult cod. Sharks, including the spiny dogfish 
(Squalus acanthias ) are perhaps their chief enemies. Other predaceous fishes such 
as the goosefish (Lophius) and the pollock ( Pollachius virens ) prey upon cod, although 
the latter can scarcely be considered a formidable enemy except to the very young. 
The cod itself is cannibalistic, although I have never known one to contain in its 
stomach another larger than 12 inches in length. However, it is common to see fresh 
s That some do survive is proven by the fact that a number of very large cod have been recaptured, some of them a year or 
more after tagging. 
