166 ADULT HEEEINGS 



1917 when they were five years old, and were also largely pre- 

 ponderant in 1918 and 1919. 



There is a school of thought which challenges the efficacy of 

 this scale reading, and it may, of course, be able to discredit it. 

 But if Hjort and Lea are correct, it is obvious that they are 

 within measurable distance of being able to make a forecast — 

 years ahead — of the Norwegian herring harvest, and to explain 

 the fluctuations which have puzzled so many generations of 

 fishermen. 



Their main conclusions are that the age of the fish prepon- 

 derating in the stock of herrings varies very greatly from year 

 to year, or in Hjort 's own words : 



' The age composition of a fish stock varies exceedingly ; 

 there are good and bad years, producing annual classes rich or 

 poor in individuals ; favourable and unfavourable conditions 

 must thus vary in nature, and seem to affect specially the 

 earher phases in the hfe of the fish, inasmuch as we perceive 

 that in advanced years the numerical preponderance of an 

 annual class is equally perceptible for a number of years. . . . 

 Wherever there is a good opportunity of obtaining representative 

 samples showing the age composition of a fish stock, it should 

 be possible to predict the composition of that stock for the 

 following years. . . . The results here mentioned have been 

 obtained through laborious investigations occupying many years, 

 involving the study of the fishes at all seasons, in order to prove 

 that the various growth rings of the scales really correspond to 

 seasonal changes.' ^ 



Norwegian Scale-reading Methods 



Scale reading in Norway, then, resolves itself into the follow- 

 ing procedure : (1) A sample of herrings is obtained from a 

 certain ground. - (2) The size and sexual development of each 

 fish is noted. (3) The scales are examined, the winter rings 

 counted, and the age of each fish is determined. The results 

 were plotted as follows for samples of ' fat ' herrings caught 

 off the north const of Norway in the autumn : 



It was noted that the fat herrings of 1907 consisted mainly 



^ Depths of Ocean, p. 768. It is surely quite easy to obtain (as indeed Storrow 

 has done) samples representative of tlie catch at any British port. 



