14 
BULLETIN OF THE BUREAU OF FISHERIES 
SUMMARY OF LOSSES 
These various losses of tags and tagged fish might be estimated as follows: 
(1) Death rate due to tagging and occurring soon thereafter, 5 per cent; (2) deaths 
due to old age, disease, enemies, etc., occurring within the first year after tagging, - 
10 per cent; and (3) fish losing their tags during the first year, 60 per cent. 
Within the first year after marking about 3 per cent of the Nantucket tagged 
cod have been reported recaptured and, if 2 per cent be allowed to cover those fish 
whose records are not received, the total recovery for this period may be set at 5 per 
cent. This, added to the 75 per cent loss just described, would leave approximately 
20 per cent of the fish at liberty with their tags still attached at the end of one year. 
If this same rate of loss continued there would remain by the end of the second year 
only about 4 per cent of the original number of fish that were tagged. 
The results have so far agreed very well with this theoretic expectation of tag 
returns, for out of 24,450 cod tagged to the southward of Cape Cod from 1923 to 1928 
the recaptures reported up to the end of 1929 are divided according to time intervals, 
as follows: 630 fish were retaken within the first 12 months after marking; 160, within 
13 to 24 months; 10, within 25 to 36 months; 1, within 37 to 48 months; and 1 was 
retaken more than 48 months later. As this experiment covered six years of tagging 
and an additional year during which tag records could be received, the mean period 
was about three and one-half years. 
Compared with this temporal segregation of recaptures, the following results 
were reported from several of the European cod-tagging experiments : 
Table 8 . — The numbers of cod recaptured during certain marking experiments in European waters 
arranged according to the duration of time they were at liberty 
Reference 
Time in months 
12 
13-24 
Over 24 
Number 
1, 416 
Number 
139 
Number 
7 
315 
19 
3 
40 
2 
0 
♦ 
If it were not that the tags dropped from the tails of so many of the fish, and if 
we knew how many, if any, of the cod died as a result of being tagged, the proportion 
of tagged fish retaken and the time element would be a most important basis for 
deducing the decline in numbers of a particular stock of cod, hence of the drain to 
which it might be subjected by the fishery. As it is, however, our returns do not 
afford the basis for calculations of this sort nor can the value of a tag record be des- 
ignated numerically, too much depending on the locality of tagging, on the average 
size of the individuals making up the stock of fish, on the intensity of the local fishing, 
and perhaps on other factors of which we are not aware at present. 
