772 
BULLETIN OF THE BUREAU OF FISHERIES 
COMBINED INDEX OF ABUNDANCE 
In years when fishing conditions favored the traps the gill net measure of abun- 
dance was usually lower owing to the toll exacted by the traps, but when conditions 
were reversed, as in 1915 and in 1926, the gill net index was the higher. Since the 
two measures are thus somewhat interdependent, neither one gives as clear a picture 
of the actual abundance as the two considered together. Therefore, the two have 
been combined. 
In making the combination each index was, from 1896 to 1934, expressed each 
year as a percentage of its average over the whole 39-year period. In each year 
each percentage was then weighted in accordance with the percentage of the com- 
bined trap and gill net-caught sockeyes that had been taken by that form of gear. 
The weighted percentages were then combined to form the final index, which is 
given by 4 -year cycles in table 34. 
EXPLANATION OF CHANGES IN ABUNDANCE 
Having reviewed briefly some of the causes of changes in the sockeye fishery, the 
question arises as to the present state of the fishery and the present state of abun- 
dance. In order to arrive at any reasonable conclusions account must be taken of 
the changes that have occurred within each cycle of 4 years — four years, as men- 
tioned above, is the age at which the majority of the Fraser River sockeye mature — 
in regard to the size of the spawning escapements, and the extent of the areas seeded 
Table 34 . — Abundance by cycles of Fraser River sockeyes 
Year 
Combined 
index of 
abundance 
Year 
Combined 
index of 
abundance 
1896.... 
134.1 
1899 
236.0 
1900 
69.4 
1903___ 
72.6 
1904. 
48.3 
1907 
40.2 
1908 
78.8 
1911 
46.5 
1912 
79. 1 
1915 
33.4 
1916. 
29.3 
1919 
23.3 
1920. 
39.9 
1923 
24.5 
1924 
43.7 
1927. 
43.2 
1928 
28.1 
1931 
29.6 
1932 
45.9 
Year 
Combined 
index of 
abundance 
Year 
Combined 
index of 
abundance 
1897 
411.7 
1898 
132.4 
1901.... 
421.4 
1902.. 
126.4 
1905 
374.7 
1906.... 
96.4 
1909. 
299.3 
1910. 
89.2 
1913. 
377.5 
1914.. 
80.8 
1917 
90.1 
1918.... 
19.0 
1921 
35.6 
1922 
35.4 
1925 
42.6 
1926 
70.3 
1929.... 
39.8 
1930... 
69.3 
1933 
49.8 
1934. 
75.6 
The providing of a large number of spawners, while of importance, cannot achieve 
permanent rehabilitation unless these spawners are members of several different “races” 
or “colonies” of sockeye, so that they will migrate to many different lake systems. 
Such a distribution of spawners will insure ample spawning gravel for the adults, will 
guard the fishery against failure when on occasion unfavorable conditions of weather 
or enemies destroy the spawning of any single lake system, and will give a greater 
stability to the fishery as it is far better to have successive waves of migrating adults 
passing through the gear, than to have the whole season’s migration occur in a very 
few weeks, as may easily happen when the total migration is to one lake system. A 
clearer conception of these waves of migration may be gained by thinking of the main 
river merely as an extension of the salt water channels up which different races of 
fish migrate to their spawning grounds on several independent lake systems. The 
principal lake systems of the Fraser River, the tributaries of which are sockeye 
spawning grounds, are shown in figure 25. 
