62 
BULLETIN OP THE BUREAU OP FISHERIES 
of each growth period is probably slower than indicated, while that at the height 
of the growing season is somewhat more rapid. The data available, however, 
do not lend themselves to a more detailed analysis. 
The general form of the growth curve thus obtained is typical and consists of a 
series of steps, rising rapidly during the summer season and more gradually during 
the rest of the year. Similar growth curves have been presented by a number of 
authors and have been obtained by the writer in an unpublished study of young 
steelhead trout. For the sake of comparison, the data given by Fraser (1917) 
for the size of chinook salmon taken in the Straits of Georgia have been indicated 
I00\ 
90 
60 
so 
40 
o 
/ 
/ 
7 
/ 
o 
y 
1 
(■ 
^ ^ ^ ^ I ^ ^ I ^ ^ 
j THIRD YEAR j FOURTH YEAR ] FIFTH YEAJi j 
Fig. 23. — Growth curve of chmook salmon that migrated seaward after spending one year in 
fresh water (scales with stream type of nuclei). For explanation see Figure 22 
on the figures. Fraser gives the size of fish of the different age groups at the end of 
each year as calculated from scale measurements. Since he has considered April 1 
as marking the beginning of the new growth period, his data for the length of fish 
at the end of each year have been placed on the ordinate corresponding to this date. 
His data are not exactly comparable with ours, since his measurements do not 
include the caudal rays, while ours do so. On this account his figures fall con- 
sistently below those for the Columbia River fish but near enough so that it seems 
probable that the differences are due almost entirely to the different measurements 
used. There is very little variation in these differences, Fraser's figures being 6 
to 10 cm. lower than ours. 
