60 
BULLETIN OF THE BUREAU OF FISHERIES 
late are small. Such characters might, however, fluctuate from year to year, 
so that samples collected in other seasons might not show exactly the same effect. 
It is not necessarily to be expected that the trends of the fish of different age groups 
taken inside will run parallel with each other, even though they do not run parallel 
with the trends for the fish taken outside. It may well happen that at any given 
time one race of fish will predominate among the fish of one age group, and that an 
entirely different race will be predominant in another age group. The evidence 
is not available to prove this for the Colimibia River chinook salmon, but Gilbert 
has shown, in his extensive studies of the sockeye salmon, that different races 
may show quite different distributions among the different age groups. It may 
be inferred that similar conditions would be found among the chinook salmon if 
sufficient evidence were available. The possible effect of such a succession of 
different races should be carefully considered in any detailed study of growth in 
which this factor may have an opportunity to operate. 
It has been shown that there are probably no radical changes in the racial 
constitution of the fish found in the ocean outside the mouth of the river. It has 
also been shown that the fish taken in the ocean are, in varying measure, immature, 
and that many of them are not destined to enter the river during the year in which 
they are taken. In consideration of these facts, it seems reasonable to suppose 
that the increase in size of the fish taken in the ocean reflects, with reasonable 
accuracy, the true effect of growth. If this be true, it is evident that most of the 
growth of the year takes place during the fishing season — that is, during the late 
spring and summer. This is shown by the fact that the fish of any one of the 
age groups are, at the end of the season, nearly equal in size to the fish of the next 
older age group at the beginning of the season. This is quite to be expected since 
it has been shown by numerous studies on various fish and other marine and fresh- 
water organisms that the main growth occurs during this part of the year. Fraser 
(1917) has shown that the chinook salmon found in the Straits of Georgia make 
their most rapid growth during this season — 80 per cent of the total growth of the 
year taking place during the months from April to September, inclusive. These 
figures must, however, be considered as very general, since in computing them 
Fraser made use of the yearly increment of growth in fish of aU age groups. In 
his investigation of the growth of the Pismo clam, Weymouth (1923) found that the 
period of most rapid growth usually came during May to September, inclusive. 
The writer (Rich, 1920) has shown that the period of most active growth in young 
chinook salmon previous to or during their seaward migration occurs during the 
spring and summer but varies somewhat with the locality. In the Columbia 
River, the most rapid growth occurs between May and September, inclusive, 
and in the Sacramento River from March to July, inclusive. Weymouth points 
out that the rate of growth is profoundly affected by variations in temperature, 
being induced and accelerated by higher temperatures. The earlier occurrence 
of the period of most rapid growth in the young salmon of the Sacramento River, 
when compared with those in the Columbia River, is undoubtedly due to the 
earher warming of the Sacramento water. Numerous other examples, showing 
that the most rapid growth occurs dm^ing the spring and summer, might be cited, 
and it seems certain that for most organisms the more rapid growth occurs during 
the warmer part of the year. 
