Fishery bulletin of the Fish and Wildlife Service - NOAA

FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 269
In figures 8 and 9 is presented the relationship between the percentage of fish
of a particular fresh-water history in the escapement and the percentage of fish of the
same fresh-water history in the return. There is a positive correlation between the
the two variables, although the relationship is very peculiar. For each 1 percent of
three-fresh-water fish in the escapement there is approximately 0.75 percent of threefresh-water
fish in the return, and for each 1 percent of four-fresh-water fish in the
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100
80
60
40
20
O SPRING RUN
D FALL RUN
22
O ZO 40 6О 8О
Pb'CîCfc'NTAGE OF TWO-OCFAN FISH IN t'SCAPfMKNT
.—Percentage о/ two-ocean flsh in return plotted against perceiitage of two-nemo fish in esrape/nent for the yeers 1922 end
1924 to 1929, inclusivo. The straight lino represents a ratio of 1 to 1.
escapement there is more than 2 percent of f our-fresh-water fish in the return. Such
a. condition could not have prevailed for any great length of time. Obviously, if such
a relationship had existed for several complete cycles, the three-fresh-water fish would
disappear from the population and only those that migrate to the ocean in their fourth
year would remain.
The age analysis based on scale samples collected during 1916, 1917, 1919, and
1921 (Gilbert and Rich, 1927), demonstrated 88.5, 88.1, 91.3, and 93,4 percent,
28
100