764 



DEPTHS OF THE OCEAN 



Both the scales represented belong to herrings six winters 

 old and represent true averages of growth, which has obviously 

 been very different in the two types. 



While studying the growth of Gadidae, Damas conceived 

 the idea that by examining the growth -history of single 

 individuals, as depicted in their scales, one should be able to 

 determine the localities, or at least the conditions, in which the 

 individuals had grown up, in other words that this study 

 should afford a key to the migrations of the fishes ; thus he 

 considers it probable that a certain saithe captured on the west 

 coast of Norway may be recognised as having spent its 

 infancy on the north coast of Norway. Similar ideas have 



Fig. 559. 



Diagram of herring scales of average growth. A, from the north-eastern part of the North Sea ; 



B, from the Kattegat. 



been expressed by Lea after studying the scales of herring. 

 He discovered that among the fat-herrings of northern Norway 

 the ones born in 1904 could be seen to have had an exceedingly 

 poor growth during their third year, the summer-belt in the 

 scales being strikingly small in that year (see Fig. 560). This 

 peculiar feature was in that year limited to a certain part of 

 the coast. The individuals thus " marked " were, however, in 

 subsequent years when increasing in age found to have a much 

 wider distribution, extending to the west coast of Norway and 

 other localities. He considers this as significant of migration, 

 and even attempts to calculate the percentage of the herrings 

 taken on the west coast that had spent their infancy in 

 northern Norway. 



