SALMON AND SALMON FISHERIES OF SWIFTSURE BANK 
813 
In 1913 the purse seiners were fishing primarily for sockeyes. Consequently, when 
the sockeye run was over the seiners quit; only 4 out of 272 catches being made in 
the last week of the 5-week period covered, and 89 catches being made in the first 
week; before the pinks wore really abundant. For this reason the difference in level 
of the curves in 1913 cannot be considered significant. In 1925 the purse-seine curve 
is considerably higher than the northern trap curve, but the data do not suggest any 
reason for this difference. 
The purse seines take large quantities of pink salmon from the areas north of 
Deception Pass, and the close correspondence with the northern trap index would 
seem to indicate that the 
southern run does not con- 
tribute much to their catch. 
Correlating the northern 
trap index with the average 
purse-seine delivery gives a 
coefficient of correlation of 
.8468 with a probability of 
less than .01. Such a high 
correlation certainly indi- 
cates that they are drawing 
largely upon the same gen- 
eral population. 
CHUM SALMON 
By George A. Rounsefell 
GENERAL LIFE 
HISTORY 
Chum salmon spawn in 
the lower tributaries of the. 
main rivers of the region as 
well as in a great many of the smaller streams. They are the latest running of the 
Pacific salmons; although there a're runs that reach some streams as early as Septem- 
ber, the bulk of the run is much later. In earlier years chums were often seined in 
salt water as late as January. As with the pink salmon, the chum-salmon fry, upon 
emerging from the gravel of the spawning beds, migrate to salt water. 
Because less is known of the life history of the chums than of the other species 
of Pacific salmon, data were collected during the 1935 fishing season on several 
hundred adults. Out of 890 individuals taken in Admiralty Inlet between October 1 0 
and November 11, the scales could be read for age on 875. Of these there were 334 
three-year-olds, 463 four-year-olds, and 78 five-year-olds, or percentages of 38, 53, 
and 9. However, none of these percentages are more than an indication of the true 
proportion, since the percentage of 3-year-olds increases, and that of 5-year-olds de- 
creases, as the season progresses. 7 These ages compare favorably with those reported 
by Pritchard (1932) in Johnstone Strait, except that we had fewer in their fourth year. 
Figure 29.— Showing two measures of the abundance of pink salmon. One measure 
is an index calculated from the catches of Puget Sound traps located north of De- 
ception Pass. The other measure of abundance is the average weighted purse-seine 
delivery for the period from August 5 to September 8, inclusive. The average 
purse-seine delivery has been plotted to one-tenth scale to facilitate comparison 
between the two measures. Note their close correspondence. 
7 These chum salmon ages were read by Milton Lobell. 
