Fishery bulletin of the Fish and Wildlife Service - NOAA

SALMON RUNS OP THE COLUMBIA KIVEK IN 1938 133
greatly increased on account of the closed season from August 25 to September 10.
The explanation is obvious. A very large part of the total catch of chinooks in the
river below Bonneville is made by means of gill nets, and this type of gear is selective—taking
more of the larger fish and permitting most of the smaller ones to pass
through. During the closed period this selection is not operating, and both large
35
30
f 25
О
g 20
Z
ÜJ
о
UJ
g 10
8 cr
I I I I I I I I I I I I I I I I I I I I I I I I I I I I I
Ч 3 «n
(9
FIGURE í.—Percentage of grilse in the Bonneville count for 1938, by weeks.
and small fish pass through the lower river and arrive at Bonneville with their proportions
practically unmodified.
The grilse passing Bonneville during the 2 weeks ending September 10 and 17
(the weeks in which the run has been least affected by the intensive fishery in the
lower river) form approximately 10 percent of the total count, so that it seems probable
that this figure is not far from the correct one for the fall run as a whole.
This is approximately half of the percentage of grilse found both earlier and later hi
the season—a fact which supports a previous conclusion based on quite different
449668—42 5
О
О
О г
а
ы о