ee 
at the time, and drawing conclusions, from measurements of the length of the fish, as 
to the age of the cod, and the composition of the stock in this respect. These measure- 
ments led me to suppose that the Finmark cod were fish of rapid growth, the stock 
consisting of only a few year classes. 
Methods of age determination adopted in the investigations. 
In 1904, the German scientist, F. HEIncke, laid before the International Coun- 
cil, at their meeting in Amsterdam, the results of his investigations directed towards 
the determination of age in the case of cod and plaice, based on a study of the bones 
of the fish*). In view of my own endeavours in a like direction, I naturally followed 
this new developement with the keenest interest. I took the earliest opportunity of 
becoming acquainted with Prof. Hrıncke’s methods, and visited Heligoland for the 
purpose. Immediately on my return I endeavoured, with the valuable assistance of 
my then Assistants Dr. H. Broc#, Dr. K. Daut, and Dr. D. Damas, to work out some 
practical method for age determinations on an extensive scale, embracing all the most 
important species of fish. The investigations carried out by Dr. Damas**) with regard 
to the cod, and those of Dr. Broc# ***) and Dr. DAHLŸ) concerning the herring, led to 
the result that the scales of the fish were selected as offermg the most advantageous 
means of ascertaining the composition of the stock in point of age. 
With this end in view, a mass of material was collected during the following years, 
consisting of scales of cod and herring, numerous measurements also being made of fish 
taken at different places along the Norwegian coast. An international commission was 
also formed to investigate the natural history of the cod species in the North Sea. The 
work of dealing with the scale material was entrusted to the gentlemen above mentioned, 
Dr. Hetzanp-HansEen}+) assisting in the work of the statistical treatment of the 
measurements. 
The principal results of these investigations, the outcome of mterested co-operation 
between those engaged upon the work, amounted, in brief, to a recognition of the fol- 
lowing facts: 
1) That the stock of cod and herring included a far greater number of year classes 
than had previously been supposed, and 
2) That the relative numerical values of these year classes exhibited great fluctua- 
tions from year to year. 
Representative biological or vital statistics. 
These conclusions furnished a definite basis for future investigations as to the fluc- 
tuations of the fishery. In a lecture delivered at the meeting of the International Council 
*) Vide Heıncke’s reports in „Die Beteiligung Deutschlands an der Internationalen Meeres- 
forschung“. Berlin, 1904, 1906 and 1908. 
**) Contribution à la Biologie des Gadides. Rapports et Proces-verbaux Vol. X, Copenhagen 1909. 
. *#**) Norwegische Heringsuntersuchungen während der Jahre 1904-1906. Bergens Museums 
Aarbog 1908, Nr. 1. 
+) The Scales of the Herring. Rep. Norw. Fishery and Marine Investigations, Vol. II, 1907, 
No. 6. 
++) Statistical Research into the Biology of; the Haddock and Cod in the North Sea. Rap- 
ports et Proces-Verbaux Vol. X, Copenhagen 1909. 
