Fishery bulletin of the Fish and Wildlife Service - NOAA

116 FISHERY BULLETIN OP THE FISH AND WILDLIFE SEBVICE
were made 1 week later than that indicated by. the marginal date, the Bonneville
count and the estimated catch above Bonneville were made 2 weeks later than that
indicated by the marginal date, and the Rock Island count 4 weeks later. For convenience
we shall refer below to the assumed position of the fish during their upward
migration as in Zones 1 and 2 the first week, in Zones 3 to 5 the second week, at Bonneville
and in Zone 6 the third week, and at Rock Island the fifth week of their freshwater
migration. The same system was followed in preparing the similar tables for
the other species.
Thus, reading across any one line, say the line for May 7 in table 12, the first column
gives the estimated catch made in Zones 1 and 2 during the week ending May 7,
the second column the estimated catch made in Zones 3 to 5 during the week ending
May 14, the fourth column the count at Bonneville during the week ending May 21,
the fifth column the estimated catch above Bonneville during the week ending May 21,
and the seventh column the count at Rock Island during the week ending June 4.
Columns 3 and 6 are derived by summing across the rows in the appropriate columns
and therefore show totals for the run as a whole—all referred back to the week that
the fish were presumably in the extreme lower part of the river and, therefore, approximately
to the time that they entered the river.
Individual fish undoubtedly vary greatly in respect of their rate of travel upstream,
but the obvious similarity in the trends of all the columns in this table is
evidence that, on the average, these assumptions are well founded.
NATURE OF THE ANALYSIS OF RUNS
From the tables of this structure it is possible, for those species that largely spawn
above the site of the Bonneville Dam, to estimate the number of fish of each species
that escaped the intensive fishery below Celilo Falls (the upper limit of commercial
fishing) in 1938 and were available for reproduction above Bonneville Dam. This is
readily done for any desired portion of the season by subtracting the catch above
Bonneville from the Bonneville count. Such an estimate of the escapement is subject
to error from several causes, of which the following may be mentioned: (1) Error in
the count of fish of the different species at Bonneville, (2) error in the catch figures
due to the fact that a considerable catch that does not appear in the record is made by
Indians, and to some extent by Whites for home use, aod (3) error in converting
pounds to number of fish. While these sources of error are present, it is believed that
their total effect is relatively small and will not affect the general conclusions that
may logically be drawn. Furthermore, in making these estimates no attempt has
been made to correct for the spawning that takes place in the tributaries below
Bonneville Dam. In the case of the silver and chum salmon such a large percentage
of the spawning takes place below Bonneville that a similar analysis has not been made.
Also, as mentioned above, there is a considerable part of the fall run of chinooks
that spawns below Bonneville so that our study of the fall run is probably less reliable
than that for the spring season. Since our estimate of the escapement is based
primarily upon the count at Bonneville (from which is subtracted only the estimate
of the number of fish in the recorded commercial catch above Bonneville) the spawning
in the tributaries between Bonneville and the upper end of the commercial fishing
district at Celilo Falls will not affect the results. If any considerable portion of the
run that is actually derived from the tributaries below Bonneville be ascribed to the