— 159 — 
one among them being specially predominant, we have then to reckon with many and 
various factors. In any case, the influence of each individual year class will be depen- 
dant upon those general laws which govern the life cycle of the species; it is therefore 
of primary importance to ascertain the nature of these laws, before it is possible to under- 
stand the complicated conditions which prevail among the stock on account of the many 
different year classes in its composition. 
In considering the question of the longevity or mortality of the cod, it will be natural 
to commence with the analyses of age of the skrei samples examined. The relation bet- 
ween age and size once determined, we are then in a position to obtain valuable infor- 
mation from the far more extensive material at hand in the form of measurements. Age 
determinations exist only for the three years 1906, 1907 and 1913. The following table 
shows the percentages of the respective year classes in these samples: 
Percentage of year classes 1906—1894 in skrei samples 1906, 1907 and 1915. 
1906 1905 1904 1903 1902 1901 1900 1899 1898 1897 1896 1895 1894 
1906. : a a4 as Wy 2205373, 3215 1.921308 
I à Ay Fe . 5 05 18.105 2836 260 77013 
19s, . Ge We Ae) Abi (ey) ek: 
Majority of skrei between 7 and to years old. 
From this it will be seen that none of these samples contained as much as 10 % 
of any single year class over 10 years old. The highest percentage for 11 year fish is 
7.7 (in 1907), for 12 year olds 4.3 (in 1906) and for fish of 13 vears 2.4 (in 1915). In the 
three years in question, only the 8, 9 and 10 year old fish play any important part in the stock. 
The stock will thus have become almost entirely renewed in the period from 1907 to 1915. The 
year classes 1902, 1901 and 1900, which in 1907 formed the youngest part of the stock, 
(the 5—7 year old fish) would in 1913 be among the oldest, and thus represented by 
only small percentages. 
Tt is now a question whether the three years can be taken as representing the general 
and permanent conditions prevailing among the skrei, a point which can obviously only 
be finally determined by long experience. The further material available consists of 
the measurements already noted in the table on p. 92 and the statements of the fishery 
authorities. According to the measurements, the three years 1906, 1907 and 1913 would 
not seem to be entirely representative; in particular it is noticeable that in certain years 
(1903) a greater number of young fish (6 and 7 years old) may be present than was the 
case in these years. On the other hand, 1907 shows a higher percentage of old (large) 
fish than any other year included in our measurements, but not so high an average 
weight as that of the years 1908 and 1909. (See Fig. 99.) 
Number of spawning years per fish. 
I have looked through the Lofoten reports from 1860 to 1902; in these 53 years, 
the average weight of the skrei (gutted weight) varied between 1.45 (in 1904) and 3.3 
(in 1889). These averages correspond, according to my weighings and measurements 
of skrei in 1913, to the size groups 65—69 and 85—89. These should form the limits 
of the field of variation of the average size. Judging from the age determinations, we 
may suppose that this factor would vary between 6 and 11 years, chiefly however, from 
