Fishery bulletin of the Fish and Wildlife Service - NOAA

SALMON RUNS OP THE COLUMBIA EIVEB IN 1938 143
might have been the result of misidentification of this species in the Bonneville count—
steelheads being mistaken for the much more numerous chinooks. In order to test
the possibility of such misidentification on a large scale in the Bonneville count, a
study was made of the ratios of the number of steelheads to chinooks in (1) the catch
below Bonneville, (2) the Bonneville count, and (3) the catch above Bonneville for
each week over the period beginning June 5 and ending October 29. It is to be
expected that such series of ratios would vary over the entire period with the relative
numbers of fish of the 2 species, but the general trends of the ratios should be
similar in the 3 localities in the absence of disturbing factors—such as misidentification
in the Bonneville count. Figure 8 is a graph of these ratios wherein ordinary
arithmetic coordinates are used, since the absolute values are the significant ones.
It is apparent from this that the trends are very similar in the 3 localities; which is
evidence that the identification at Bonneville was sufficiently accurate and probably
was not responsible for the anomalous fact that more fish were recorded in the commercial
catch above Bonneville than were counted over the dam.
The data thus graphed are interesting in themselves in addition to their bearing
on this particular problem. It is quite obvious that, in numbers of fish, the steelheads
approach the chinooks and, during the June-July period when chinooks are
few, greatly exceed them. It is chiefly during the peak of the chinook run in August
and September that the ratio is down to about 1:5 in the catch below Bonneville
and the Bonneville count. The parallelism in the 3 trends up to about the middle
of September is quite striking and is supporting evidence that, for this part of the
run, the assumed rate of travel is satisfactory.
SILVER AND CHUM SALMON
As mentioned in the introduction, the purposes of the original report by Calkins,
Durand, and Rich were such that consideration of the catches of silver and chum
salmon was not important. In this revision, however, it is pertinent to include the
data available on these 2 species, and to examine these for whatever light they may
throw upon the characteristics of the runs. The general features of the runs of silvers
and chums are so similar that it is convenient to treat them together.
The data for these species are given in modified form in tables 25 and 26. In
converting poundage to numbers of fish an average weight of 10 pounds per fish has
been used for both species. The same rate of migration up the river has been used as
with the other species, although the rate of migration of both (silvers and chums is
more doubtful and of far less significance than in the case of the other species. There
is, however, no good evidence that the rate of travel is any different in the case of
these 2 species than in the others, although the obvious irregularities in the time at
which the main portion of the catches is made in the different zones (tables 4 and 5)
lead one to suspect that the rates of travel of these species may be somewhat different.
This is a matter that should be investigated, but it is necessary for the present to
assume the same rate of travel—which has been done in preparing the modified tables.