48 



Transactions. 



From the AccUmatization Society's records I have calcrJated the 

 average length of the fish tagged each year since 1915. The figures in 

 parentheses give the number of fish measured : — 



1915— Males, 20-8 in. (100) ; females, 20-1 in. (98). 



1916— Females, 19-3 in. (199). 



1917— Females, 20-4 in. (140). 



1918— Males, 22-6 in. (66) ; females, 21-5 in. (156). 

 In the years 1915 and 1918, when both sexes were tagged, the males 

 averaged about 1 in. longer than the females. The average lengths of the 

 samples from which I took scales are as follows : — 



1915— Males, 21-3 in. (33). 



1917— Females, 20-4 in. (140). 



1918— Males, 22-5 in. (29) ; females, 21-7 in. (36). 

 These figures agree closely with the averages for the total fish measured, 

 so the samples were in all probability fairly representative. The year 

 1918 was remarkable both for the number and large size of the spawning 

 fish. The average ages [see Tables I (A) to I (F)] indicate that the males 

 either have a shorter life, or cease to run up the river at an earlier age. 

 This bears out the general belief that the spawning mortality is greater 

 amongst the males. 



Fig. 3. 



A point to notice in these curves is that they are nearly straight lines 

 for the first four years. This does not mean that each individual fish 

 increases in length by approximately the same amount each year up to 

 four years old. So far as my experience goes, growth of this character 

 is almost unknown amongst trout in Canterbury, although such apparently 

 is not the case in Norway. In Canterbury I have found that unless some 

 outside influence is at work the rate of growth almost invariably starts 

 to decrease quite appreciably in the third year, and this decrease is 



