Fishery bulletin of the Fish and Wildlife Service - NOAA

142 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE
the year, however, the ratio rose to nearly 10:1; i. e., about 10 fish were caught in
the river below the dam for every 1 that reached the dam. Various explanations
might be offered, but it seems most likely that, as suggested above, it is due to the
fact that a large percentage of the fish entering the river during the late fall spawn
in tributaries that enter the mam river below the dam.
We have discussed the importance of the chinook catch above Bonnevffle during
the first few weeks following the closed period, and the fact that the closed period
has more effect in spreading the catch out over a longer fishing area than it has in
the way of increasing the spawning escapement. Evidently the same effect is apparent
in the case of the steelheads. This shift in the relative importance of the fisheries
below and above Bonneville is shown somewhat more clearly by the percentages of
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FIGURE 8.—Ratio of steelhead trout to Chinook salmon In three Important elements of the 1938 run, June 5-October 28, by weeks;
the total catch formed by the catches above Bonneville (table 24). For the months
of June and July only 4.5 percent of the total catch was taken above Bonneville, but
during August and September the percentage was 36.2. The relation of this to the
net escapement also is shown by the percentages that the catch above Bonneville
form of the Bonneville count. For the months of June and July only 10.3 percent
of the fish counted past Bonneville were later captured in the fishery above the dam.
During the months of August and September, however, 43.9 percent was taken.
As with the chinooks, the catch of steelheads above Bonneville during the first
few weeks following the closed period of August 25 to September 10 exceeds the
Bonneville count. This anomaly has been discussed and there seems to be no reason
to doubt that the same factors were operating with the steelheads as with the chinooks.
It has seemed possible in the case of the steelheads, however, that this phenomenon