METHODS OF INVESTIGATION. 11 



being contracted and closer together. These contractions may be due to 

 checks or irregularities in the whole growth of the fish, or to variations in 

 the relative rate of growth in length or girth. It is easy to understand that 

 a fish which grows so rapidly and which consequently requires such an 

 enormous amount of food is very soon affected by any period of scarcity, 

 and it is evident that any such check in growth will be more or less clearly 

 indicated on the scales. In the same way a transition from rapid growth 

 in girth or thickness to a state of growth relatively more pronounced in 

 length would manifest itself by a narrowing of the growth rings at the 

 sides, and also in the front portion of the scales. These narrowings or 

 contractions in the ring formation which appear in the summer-zone are, 

 however, much less distinct than the winter-band, and one soon learns 

 how to distinguish one from the other with certainty. That they are in no 

 way connected with the winter is evident from the appearance of the scales 

 from marked fish of known age, which were examined and depicted by 

 Johnston.* 



In order to ascertain more fully the significance of these secondary 

 checks, I made an analysis of the frequency of their occurrence in a large 

 number of salmon caught in the summer of 1909 in the neighbourhood of 

 Kandesund and Flekker0 (Christiansand). Out of these I picked out only 

 those fish which had one winter-band subsequent to migration. In the 

 following table I have divided them into two classes, those with and those 

 without the secondary check (see next page). 



It will be seen that the fish whose scales show this secondary check are 

 of exactly the same average length as those without it. This could not 

 possibly have happened if this secondary contraction of the rings gave the 

 same indications as to age as shown by the winter-band. 



There is yet another difficulty which should be mentioned, as it is 

 likely to cause considerable trouble to the inexperienced. In scales taken 

 from nearly every fish one will find a greater or less number absolutely 

 different from the others. Such scales have this remarkable feature that 

 the structure of the growth-rings and the season-zones can be easily traced 

 from the outer edge of the scale for a greater or less distance inwards 

 towards the centre, and as far as this portion of such scale is concerned 

 they are exactly like other typical scales taken from the same fish. There 

 is, -however, this difference, that at a greater or less distance from the outer 

 edge of the scale all regular ring-formation disappears, and the central 

 portion of the scale, which will be of varying extent as the case may be, 

 consists of a large clear space consisting of a number of irregular stripes 



* " Twenty-sixth Annual Beport of the Fishery Board for Scotland (for 1907)," 

 H. W. Johnston. The Scales of Salmon, Figs. 1 and 2. 



